Biology 30

Morinville Community High School

Unit 5b: Classical Genetics

Name: ______________

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Chapter 17 text p. 584-621 Key Concept A: Theory of Inheritance: Gregor Mendel’s Pea Experiments & Genetics Vocabulary A1. Dominant and Recessive Genes Key Concept B: Monohybrid Crosses B1. Monohybrid Crosses & Punnett Squares & Mendel’s 1st law: Law of Segregation B2. Test Crosses B3. Multiple Alleles B4. Incomplete and Co-Dominance B5. Sex-Linked Traits Key Concept C: Dihybrid Crosses C1. Dihybrid crosses and Mendel’s 2nd law: Law of Independent Assortment Key Concept D: Beyond Mendel D1. Chromosome Mapping D2. Polygenic Inheritance Key Concept E: Human Genetic Analysis E1. Constructing a Pedigree E2. Using a pedigree to analyze problems E3. Modes of Inheritance E4. Genetic Counseling

A1. Dominant and Recessive Genes Gene: a heritable factor that controls a specific characteristic. 'Heritable' means passed on from parent to offspring 'Characteristic' refers to genetic traits such as your hair

color of blood type. Allele: one specific form or version of a gene The alleles are represented by letters. Locus: the particular location of a gene on homologous chromosomes Homozygous: two identical alleles for the gene Heterozygous: two different alleles for the gene Phenotype: the physical form of the trait of an organism Genotype: the symbolic representation of a pair of alleles of a trait of an organism, typically represented by two letters Dominant allele: an allele that has the same effect on the phenotype whether it is paired with same allele or a different one. Dominant alleles are always expressed in the phenotype. Recessive allele: an allele that has an effect on the phenotype only when present in the homozygous state.

Classical Genetics Unit Outline

Key Concept A: Theory of Inheritance

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Progeny: offspring Filial (F): First and subsequent generations of offspring (F1, F2, F3 etc) Autosomal: Non-sex chromosomes (in humans these are chromosomes 1-22) True-Breeding: Both gene copies are the same allele (homozygous).

Example: Flowers of pea plants

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Human Traits Introduction: Many of you are already familiar with many of the genetic traits of humans such as baldness, eye color, color blindness and blood types. However, other characters such as size and position of eyes, number and shape of fingers, total body size and body proportion may also be genetically determined (although such characters as body size may be profoundly influenced by environment). The tremendous number of genetic traits makes humans extremely variable. With the exception of identical twins, it is highly improbable that any two persons will have the same (or even similar) combinations of genetically determined traits. In this exercise, you will inventory yourself for the series of genetic traits listed in the table, some of which are described below. Most of these are known to be single-gene traits, expressions of two alleles at one gene locus.

Instructions: Get with a partner and determine your phenotype for each of the traits. Identify as much of your genotype as you accurately can. Record both phenotype and genotype in the table. At the end of the exercise, we will tabulate class results.

Trait (alleles) Expression 1. Bent pinky (P, p) Dominant allele causes the distal segment of the fifth finger to bend distinctly inward toward the fourth (ring) finger. Lay both hands flat on your desk and relax the muscles. Does your fingertip bend inward? My Phenotype: ________________ My Genotype: __________ 2. PTC tasters (T, t) Phenylthiocarbamide (PTC) tastes extremely bitter to heterozygous or homozygous dominant individuals, but is tasteless to homozygous recessives. Put a small piece of paper that has been impregnated with PTC on the tip of your tongue. My Phenotype: ________________ My Genotype: __________

3. Blue eyes (B, b) Are your eyes blue or some other color? Blue-eyed persons are homozygous recessive and lack pigment in the iris of the eye; heterozygous or homozygous dominant individuals have iris pigment; the actual pigmentation is a result of the interaction of several genes (polygenic trait). Brown eyes are the result of a brown pigment layer in the front of the iris. Blue eyes result when a blue layer in the back of the iris can show through in the absence of brown. Hazel or green eye color is the result of an unrelated gene that produces a yellow pigment. Hazel eyes have brown iris pigment while green eyes have a blue iris. My Phenotype: ________________ My Genotype: __________

4. Tongue rolling (R, r) Persons with a dominant allele in heterozygous or homozygous condition can roll their tongues into a tube-like shape; homozygous recessives are non- rollers and can never learn to roll their tongues. The ability to curl the tongue is probably the result of several genes(polygenic trait), though in genetics labs is usually treated as a one-gene trait. My Phenotype: ________________ My Genotype: __________ 5. Widow's Peak (W, w) Dominant allele in heterozygous or homozygous individuals results in a V-shaped front hairline; homozygous recessives have straight hairlines. My Phenotype: ________________ My Genotype: __________ 6. Interlock fingers/ Thumb crossing (C, c) The way that you interlock your fingers is genetic. Clasp your hands together quickly, interlocking the fingers. Which thumb is on top? Most people will interlock their fingers so that the left thumb is on top of the right, the dominant allele (present in either heterozygous or homozygous individuals). Those who are homozygous recessive place their right thumb over the left. (Try interlocking your fingers the opposite way from the way you naturally do this to compare.) My Phenotype: ________________ My Genotype: __________

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7. Arm Crossing (A,a) Most people will cross their right arm over the left., the dominant allele (present in either heterozygous or homozygous individuals). Those who are homozygous recessive place their left arm over the right. (Try crossing your arms the opposite way from the way you naturally do this to compare.) My Phenotype: ________________ My Genotype: __________

8. Ear lobes (E, e) Ear lobes may be either adherent or free and pendulous. Homozygous recessives have attached ear lobes ; heterozygous or homozygous dominant individuals have detached (free) ear lobes. My Phenotype: ________________ My Genotype: __________ 9. Hitchhiker's thumb (H, h) Homozygous recessives can bend the distal joint of the thumb backward to a nearly 90º angle; heterozygous or homozygous dominant condition yields thumbs that cannot bend backward more than approximately 30º. The ability to bend the thumb backward is a caused by a dominant allele. The proper term for this is distal hyperextensibility. People with dominant alleles have more flexible ligaments and thus looser joints. My Phenotype: ________________ My Genotype: __________

10. Freckles (F, f) The presence of freckles is dominant over the absence of freckles. My Phenotype: ________________ My Genotype: __________

11. Shorter Big Toe (B,b) The dominant allele for toe length results in a big toe shorter than the second toe. If your big toe is longer than your second toe you have recessive alleles for this trait. My Phenotype: ________________ My Genotype: __________

12. Short Palmar Muscle (M,m) Examining the tendons that run over the inside of the wrist can tell you if you have the recessive long palmar muscle or the dominant, shorter palmar muscle. Those who are dominant have two tendons. Those recessive have three tendons. To determine this, you must clench your fist and flex your hand. Look and feel for three tendons. A middle tendon indicates the presence of the recessive long palmar muscle. My Phenotype: ________________ My Genotype: __________ Questions: 1. Which traits, the dominant or the recessive, are you able to determine the genotype for? Why? 2. Which traits, the dominant or recessive, are you not able to determine the genotype for? Why? 3. In a sample population (i.e. the students in this class), does the dominant trait always represent the highest frequency and the recessive trait the lowest frequency? Support your answer with data from the class.

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B1. Monohybrid Crosses & Mendel’s 1st Law of Segregation

• In his first set of experiments, Mendel investigated the pattern of inheritance of one set of traits. His one-trait experiments have been categorized as monohybrid crosses.

• The observed results of Mendel’s monohybrid crosses with

pea plants resulted in Mendel’s First Law: the Law of Segregation

Mendel’s Law of Segregation: Every individual has 2 copies of each gene (1 on each homologous chromosome) When any individual produces gametes, the copies of the gene separate (segregate) so that each gamete only receives one copy. If an individual has 2 different alleles, the gamete will receive one or the other. Tips: When completing any type of classical genetics cross, use the following problem solving steps: * Create a key or legend for your traits (what letters you’re going to use, what is dominant, recessive etc) * List the genotype of the parents & show the cross * Draw a punnet square * Check your work

Examples 1. In peas, green pod color is dominant to yellow pod color. Show a cross between true-breeding (homozygous) green and true-breeding yellow plants. This first cross is your parental (P1) generation. Carry out the cross through the F1 and F2 generations. Show phenotypes, genotypes, and the phenotypic and genotypic ratios for all generations. 2. In poultry, rose comb is dominant to single comb. a. Cross a true-breeding rose-combed rooster with a single-combed hen. Then cross the F1's to produce an F2 generation. Show all genotypic and phenotypic ratios. b. Explain how it is possible for a rose-combed rooster and a rose-combed hen to produce single-combed offspring. What percentage of the offspring are expected to have single combs in this cross? 3. Consider blue eyes in humans to be recessive to brown eyes. Show the expected children of a blue-eyed woman with a brown eyed man whose mother had blue eyes. Show the predicted genotypic and phenotypic ratios of their children. State what you know (and don't know) about the brown-eyed man's father based on the information given here. What can you predict about the brown eyed man's brothers and sisters?

Key Concept B: Monohybrid Crosses

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4. In domestic swine there is a dominant allele which produces a white belt around the body. The recessive allele produces uniform body color. One farmer wants to produce only belted hogs, and another wants only uniformly colored animals. Which farmer would have an easier time producing a true-breeding herd? Explain why. Tell how each farmer would proceed. (Hint: how could you tell if a herd were true-breeding?) 5. In cattle, the polled (hornless) condition is caused by a dominant allele, while the recessive allele causes horns to grow. A polled cow and a polled bull produce a calf which grows horns as it matures. Show the genotypes of all three. What is the probability that the pair's next calf will also grow horns. 6. Albinism in corn is caused by a recessive allele, and is normally lethal because the plant cannot manufacture food without chlorophyll, so dies after it has exhausted the food in the seed. It is possible experimentally to keep albino plants alive with special feeding techniques in which sugar is supplied to the plant through the leaves. Show the expected offspring from a cross between an albino plant and a normal plant that is heterozygous for albinism.

7. In Holstein cattle, spotting of the coat is caused by a recessive allele and solid coat color by a dominant allele. What types of offspring can occur in a cross between two spotted animals? 8. A woman has a rare eyelid abnormality called ptosis, which makes it impossible for her to open her eyes all the way. The condition is caused by a single dominant allele. The woman's father had ptosis but her mother was normal. Her father's mother also had normal eyelids. a. What are the genotypes of each of the people mentioned above? b. What proportion of her children would be expected to have ptosis if she marries a man with normal eyelids? 9. In garden of pea plants, a purple-flowered true breeding plant was cross-pollinated with a white-flowered plant (purple is dominant to white).

a) What are the phenotypes and genotypes of the F1 progeny?

b) If the monohybrid flowers are crossed, what are the phenotypes and genotypes of the F2 progeny?

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10. Black fur on guinea pigs is dominant over white fur. A black, pure breeding guinea pig was crossed with a white guinea pig.

a. Determine the phenotypic and genotypic percentages when the F1 individuals are crossed.

b. If the F1 generation was crossed, what are the phenotypic and genotypic ratios of the F2 progeny?

11. Tay-Sachs is an autosomal recessive genetic disorder. Carriers of Tay-Sachs are always heterozygotes and do not show any symptoms, however are capable of passing on the recessive allele to their offspring. Tay-Sachs carriers are found most frequently among the Jews of East European origin (Ashkenazi Jews) with a rate 100 times higher than the general population. Tay-Sachs is a fatal condition that causes deposition of unmetabolized intermediates in the nervous system. Affected infants are normal at birth, but by the age of 6 months they become listless and weak and show difficulty in feeding. Sudden noises provoke an exaggerated startle reaction. Around 12 months of age there is a rapid decrease in mental and motor functions as well as on onset of blindness, deafness, rigidity and brain enlargement. Death usually occurs within the first 3 years of age from pneumonia or a lung infection.

a. If two carriers of Tay-Sachs decided to have children, calculate the probability of having a child with Tay-Sachs.

b. What is the probability that their adult children would not be carriers?

12. In pigeons, the checkered pattern is dominant to plain pattern.

a. Using a punnett square, show the cross between two heterozygous parents.

b. A checkered pattern female pigeon mates several times with the same male pigeon. It was noted that the female had four checkered pattern chicks and four plain pattern chicks. What is the phenotype of the male?

13. Huntington Disease (HD) is inherited as an autosomal dominant trait. HD is characterized by rapid, uncontrollable muscle movements such as tics or muscle jerks. This disorder causes a loss of coordination and personality changes. As the disease progresses, the ability to speak is impaired, memory may fade, and involuntary jerky muscle movements become more severe. The entire nervous system progressively degenerates, ultimately leading to death 10 or more years later. HD is located on chromosome 4 and most of the symptoms do not show up in the early reproductive years, therefore the gene for HD may be transmitted unknowingly to the affected individual’s children. Scientists have identified a ‘chromosome marker’ which makes genetic testing possible. After genetic testing, Charlie is informed that he is affected with Huntington Disease and his wife, Lorna, is unaffected. They wish to have children. Charlie’s father has HD and is currently bedridden. His mother is unaffected with HD. What is the probability of Charlie and Lorna having a child who is unaffected with HD?

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14. Neurofibromatosis-1 (NF-1) is an inherited disorder, characterized by tumors involving nerve tissue. Problems with sensation and movement result. NF-1 is an autosomal dominant disorder in that the allele for those affected with the disorder, F, is dominant to the allele, f, for those unaffected with the disorder. If a woman affected with NF-1, who carries one dominant allele and one recessive allele, and a man unaffected with NF-1 decide to have a child, what is the percentage probability that their child will be affected with this disorder? Support your answer with a Punnett square. 15. In rabbits, the allele for long hair, L, is dominant to the allele for short hair, l. A cross between a short-haired female and a long-haired male produced a litter of seven long-haired bunnies and one short-haired bunny.

a. What are the genotypes of the parent rabbits? Draw a punnett square to illustrate this cross.

b. What phenotypic ratio was expected in the offspring generation?

c. Considering the number of offspring, explain why a typical ratio was not produced in this instance.

16. In fruit flies, long wing, L, is dominant to dumpy wing, l. Two long winged flies mate and produce 49 dumpy-winged and 148 long-winged offspring. What are the genotypes of the parent flies?

B2. Test Cross Test Cross: testing an unknown plant or animal by crossing it with a known homozygous recessive (ex. aa) Examples 1) In mice, a condition called waltzer is recessive. A waltzer mouse has a defect in the

region of the inner ear that interferes with its balance. Consequently, waltzers run in circles. A mouse that runs normally might be homozygous dominant for this gene, or it might be heterozygous. If geneticists had several mice that walk normally, and wanted to know if any of these mice were heterozygous for the waltzer mutation, they would to a test cross. Draw two Punnett squares to show probabilities of the test cross that would help the geneticists determine the genotype of their normal mice.

2) Black wool is very brittle and is difficult to dye. A rancher can avoid getting black

sheep in his flock by only breeding homozygous dominant white sheep (WW). The rancher first has to determine if his white sheep are actually homozygous. Show how he could determine the unknown genotype of his white sheep by using a testcross with a black sheep (black sheep are homozygous recessive ww).

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B3. Multiple Alleles Multiple Alleles: A gene with more than two alleles As there are more than two alleles, upper and lower case letters are not used to signify dominance and recessiveness. Examples 1) Fly eye colour is determined by multiple alleles. There are four different

alleles that each code for a different eye colour (E1 = Red with is dominant to E2 = Apricot, which is dominant to E3 = Honey which is dominant to E4 = white).

a. Two flies mate and have 74 apricot colour eyed offspring and 30 honey colour eyed offspring. What are genotypes of both parent flies?

b. You are in the process of performing genetic experiments on flies in the lab when all of your flies escape. You manage to trap a couple of flies but you no longer know what genotype they are. One of the flies has red eyes, and the other has white eyes. When you mate the two flies your results show approximately half the progeny with apricot eyes, and the other half with red eyes. What are the genotypes of the two flies you were able to capture?

2) The gene that controls chinchilla coat colour has 4 alleles: Agouti C >

chincilla cch > Himalayan ch > albino c. Agouti coat colour must have at least one C.

a) What are the possible genotypes for agouti colouration?

b) What are the possible genotypes for chinchilla colouration?

c) What are the possible genotypes for Himilayan colouration?

d) A chinchilla rabbit with the genotype cchch is crossed with a himilayan rabbit with genotype chc. What is the expected ratio of phenotypes among the offspring of this cross?

e) Some of the offspring of a chinchilla rabbit and a Himilayan rabbit are albino. What must be the genotypes of the parent rabbits?

B4. Incomplete and Co-Dominance Incomplete Dominance: Describes a condition where there is partial expression of both alleles: neither of two alleles for the same gene can completely conceal the presence of the other. Three phenotypes exist for incomplete dominant traits with heterozygous individuals being an intermediate condition of the two alleles. Because there is no completely dominant allele, superscript notation is used in place of upper and lower case letters.

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Examples 1. The Four O'clock plant has only two alleles for flower color, but has three different phenotypes: red flowered plants, white flowered plants, and pink flowered plants. a. Show the expected offspring of a cross between two pink-flowered plants. Include genotypes, phenotypes and ratios. b. Show the expected offspring of a cross between a red-flowered Four O'clock plant and a pink-flowered plant. c. Show the expected offspring of a cross between a pink-flowered Four O'clock plant and a white flowered plant. Co-Dominance: Describes a condition in which both alleles are fully expressed.

Examples 1. In shorthorn cattle the CR allele, when homozygous, produces animals with red hair and the CW allele, when homozygous, produces cattle with white hair. An animal with a heterozygous genotype is roan in color, meaning its coat contains both red hairs and white hairs. a. Describe the expected offspring when a breeder mates cows and bulls of the following phenotypes: red x red

white x white red x roan white x roan red x white roan x roan b. Which kind of true-breeding herd would be easier to establish: red or roan? Explain. c. What is the probability of a pair of roan cattle producing (1) a red calf? (2) a roan calf? (3) a white calf? 2. A blue roan horse is a heterozygote in which one allele is expressed in the white hairs and the other allele is expressed in the black hairs. When both these colours are expressed, the horses coat color sometimes looks blue. If two blue roan horses are bred together, what is the chance that the colt will be white?

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Incomplete and Co-Dominant Examples 1. Suppose that when true-breeding long radishes are crossed with true-breeding round radishes, the F1 generations are all oval-shaped. Is this an example of codominance or incomplete dominance? 2. A green-leafed Coleus plant was crossed-pollinated with a purple leafed Coleus plant. The offspring all had spotted green and purple leaves. Is this an example of codominance or incomplete dominance? 3. The symbols IA, IB, and i represent the three alleles that control the human ABO blood group. The alleles IA and IB are codominant, and are both dominant to the i genotype. The phenotypes are stated as blood types A, B, AB, and O. Two newborn babies were accidentally mixed up in the hospital. Use the information given to answer the questions that follow. Baby 1: Type O Mrs. Brown: Type B Mrs. Smith: Type B Baby 2: Type A Mr. Brown: Type AB Mr. Smith: Type B a. Which child belongs to the Browns? Which child belongs to the Smiths? b. Indicate the genotype of everybody above if you haven’t already done so. 4. A man with blood type B is being sued for paternity by a woman with blood type A. The child the woman claims he fathered has blood type O. a. If this man is the father of the child, what are the genotypes of the parents? b. If this man's blood type were AB, could he be the child's father? Explain.

5. The disorder familial hypercholesterolemia (FH) results when a person possesses two copies of a particular nonfunctioning allele. FH is a condition that prevents the tissues from removing low-density lipoproteins (LDL, commonly known as “bad cholesterol”) from the blood. People who are homozygous for the trait have six times the normal amount of cholesterol in their blood and may have a heart attack at the age of 2. Heterozygotes, who possess only one nonfunctioning copy of the gene, have about twice as much cholesterol in their blood an may have a heart attack by the age of 35.

a) Using Ch to represent the functional (normal) allele and CH to represent the nonfunctioning (mutant) allele, identify the genotype for each of the following phenotypes:

i) Healthy. No increased risk for heart attacks:

ii) Heart attacks in middle age (35-45):

iii) Heart attacks in childhood:

b) Is the nonfunctioning allele a dominant or recessive allele?

c) How would you describe the alleles involved in FH: co-dominant, completely dominant, or incompletely dominant? Explain your answer.

d) Sophie and Stephan Grosfeuille are the parents of two young girls, Isabelle and Claire. Sadly, 14 year old Isabelle recently died from a heart attack. Sophie and Stephan knew that many members of each of their families had suffered from heart attacks but they never thought it would happen to someone so young.

i) What was the genotype of Isabelle?

ii) What are the genotypes of Sophie and Stephan?

iii) If Sophie and Stephan have another child, what is the percentage

probability of that child having the same genotype as Isabelle?

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B5. Sex-Linked Traits Thomas Morgan (1866-1945) is considered to be one of the modern father of genetics and was made famous for his extensive fruit fly experiments. He concluded that sex-linked traits are expressed in different ratios by male and female offspring, because they are governed by the segregation of X and Y chromosomes. There are much fewer genes located on the Y chromosome than on the X chromosome. Example 1. Human females are XX and males are XY. a. Does a male inherit the X from his mother or father? 2. Most people’s blood clots normally. Hemophilia is a blood disorder which causes blood not to clot properly. The allele for hemophilia is recessive to the allele for normal blood clotting. These alleles are located on the human X chromosome. The Y chromosome is a genetic "blank" for this trait; it contains no allele for the blood-clotting gene. a. A number of cases of hemophilia have occurred among male descendants in the family of England's Queen Victoria. She, however, did not have hemophilia, nor did her husband. Show the genotype of Queen Victoria and her husband that would produce this result. b. Show the possible genotypes of parents who give birth to a hemophiliac daughter. c. Explain what's wrong with the statement "That hemophiliac man's father was also a hemophiliac, so he must have inherited the disease from his father."

4. Red-green color blindness in humans is X-linked (same inheritance pattern as hemophilia). a. A woman has normal vision, but her father is color blind. Is she necessarily a carrier (heterozygous)? Explain. b. Diagram all genotypes and phenotypes of parents and expected children in a family where the woman has normal vision and no family history of color blindness, and the man is color blind. c. In a large family, all nine sons were color blind and all four daughters had normal vision. Give the genotypes and phenotypes of all concerned. 5. Red-Green colourblindness is a recessive trait that is linked to the X chromosome. The symbol XB is used to signify normal vision and the symbol Xb is used to signify colourblindness. The normal-visioned daughter of a father with colourblindness marries a man who is unaffected by colourblindness. What is the percentage of probability of having a son who is colourblind? 6. Hemophilia is a recessive, X-linked condition. Hemophiliacs bleed excessively when injured because they are missing a certain protein required for blood clotting. The most seriously afflicted individuals bleed to death after relatively minor bruises or cuts. The ancient Hebrews must have had some understanding of the hereditary pattern of hemophilia, because sons born to women having a family history of hemophilia were exempted from circumcision. A hemophiliac man is married to a woman who is unaffected by hemophilia. Some of their children have hemophilia. What are the parents’ genotypes?

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7. Pseduohypertrophic muscular dystrophy is a sex-linked disorder that causes gradual deterioration of the muscles. It is seen only in boys born to apparently normal parents and usually results in death in the early teens.

a) Is pseduohypertrophic muscular dystrophy caused by a dominant or recessive allele?

b) Provide the genotypes of normal parents producing an affected son.

c) Why is this disorder always seen in boys and never in girls? 8. Brown spotting of the teeth is caused by a dominant allele found on the X chromosome. How would the sons and daughters be affected if one parent is unaffected by brown spotting and the other

d) parent is a man affected by brown spotting?

e) parent is a woman affected by brown spotting?

B1. Dihybrid Crosses and Mendel’s 2nd Law of Independent Assortment

• In another set of experiments, Mendel investigated the pattern of inheritance of two sets of traits. His two trait experiments have been categorized as a dihybrid crosses.

• The observed results of Mendel’s dihyrid crosses with pea plants

resulted in Mendel’s second law: the Law of Independent Assortment

Mendel’s Law of Independent Assortment: The two alleles for one gene segregate (separate) independently of the alleles for other genes during gamete formation.

Key Concept C: Dihybrid Crosses

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Examples 1. A tall pea plant with terminal flowers (flowers on the ends of the stems) is crossed with a short plant that has axial flowers. All 72 offspring are tall with axial flowers. This is a dihybrid cross with the height and flower position traits showing independent assortment. a. Name the dominant and recessive alleles. b. Give the genotypes of the parents and offspring in this cross. c. Predict the F2 offspring when the tall-axial F1's are allowed to self pollinate. 2. Suppose a white, straight haired guinea pig mates with a brown, curly-haired animal. All five babies in their first litter have brown fur, but three are curly and two have straight hair. The second litter consists of six more brown offspring, where two are curly and four are straight haired. a. Can you tell which alleles are dominant? b. Assuming curly is dominant to straight, what are the genotypes of the parents and the offspring? c. What is the probability of getting two female guinea pigs with straight hair in a row?

3. About 70% of Canadians get a bitter taste from the substance called phenylthiocarbamide (PTC). It is tasteless to the rest. The "taster" allele is dominant to non-taster. Also, normal skin pigmentation is dominant to albino. A normally pigmented woman who is taste-blind for PTC has an albino-taster father. She marries an albino man who is a taster, though the man's mother is a non-taster. Show the expected offspring of this couple. 4. In pigeons the checkered pattern is caused by a dominant allele. A plain (non-checkered) pattern is recessive. Red color is also caused by a dominant allele and brown color by a recessive allele. a. Show the expected offspring of a cross between a homozygous checkered red bird and a plain brown one. Carry out this cross through the F2 generation. b. Carry out to the F2 generation a cross between a homozygous plain red bird and its homozygous checkered brown mate. c. A plain brown female pigeon laid five eggs. The young turned out to be: 2 plain red, 2 checkered red, and 1 checkered brown. Describe the father pigeon. Give the genotypes of all birds in this cross. Could any other types of offspring have been produced by this pair?

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5. In garden pea plants, the gene for plant height has two alleles: the tall allele is dominant over the short allele. The gene for pod colour has two alleles: green pod is dominant over yellow pod.

a) If Mendel crossed true breeding tall plants that had green pods with true breeding short plants that had yellow pods, what is the outcome of the F1 generation?

b) If the F1 progeny were then self-crossed, what are the phenotypic and genotypic ratios of the F2 progeny?

6. In rabbits, the allele for brown coat colour is dominant over white coat colour. The allele for short fur is dominant over long fur. A true-breeding brown, short-haired rabbit is mated with a white, long-haired rabbit. The F1 progeny were then self-crossed. Determine the phenotypic ratio and genotypic ratios of the F2 progeny. 7. In guinea pigs, rough coat R is dominant to smooth coat r. Black coat colour B is dominant to albino b. A heterozygous black, smooth coat male is bred to a heterozygous black, heterozygous rough coat female. What are the probable genotypic and phenotypic probabilities of the offspring?

8. Suppose that normal leg size in cattle is produced by the homozygous genotype DD. Short-legged cattle possess the heterozygous genotype Dd. The homozygous genotype dd, is lethal, producing grossly deformed dead calves. Also, suppose that the presence of horns in cattle is governed by the recessive allel of another gene locus, p, whereas the polled condition (absence of horns) is produced by the dominant allele P. In matings between horned, short-legged cattle, what percent of each kind of phenotype are expected in the adult offspring? 9. Suppose a colourblind male with type AB blood has children with a woman who has normal vision and no family history of colour blindness and is also type O blood. What is the probability they will have a colourblind daughter with type A blood?

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D1. Chromosome Mapping

• Mendel’s Law of Independent Assortment was based on onbservations of genes located on different chromosomes. What this means is that the segregation of an allele for a gene on chromsome #1 of the pea plant had no bearing on the segregation of alleles for a gene on chromosome #3 for example.

• Unfortunately, the law of independent assortment only

applies when genes are located on different chromosomes.

• When genes are located on the same chromosome, they

are said to be “linked” and are more likely to get passed on together.

• When two genes are linked, the closer they are together,

the less likely it is for crossing over to occur between them. The reverse is also true. The further away to genes are on the same chromosome, the more likely it is that crossing over will occur between them.

• The rate at which crossing over occurs between linked

genes is referred to as “crossover frequency” and this number is used as a relative distance between genes.

Examples 1) For a series of experiments, a linkage group composed of genes Q, R, S and T was

found to show the following gene recombinant frequencies:

Genes Q R S T Q - 3% 7% 5% R 3% - 10% 8% S 7% 10% - 2% T 5% 8% 2% -

Construct a gene map. Show relative positions of each gene on the chromosome and indicate distances in map units.

2) The genes for body colour and wing shape are found on the same chromosome in fruit flies

Two Genes Found on the Same Chromosome in Drosophila

S body colour (S = normal / s = sable)

W wing shape (W = normal / w = miniature)

In a cross between a heterozygous normal fly and a sable-bodied, miniature-winged fly the results were:

99 normal flies 99 with a sable body and miniature wings 11 with a normal body and miniature wings 11 with a sable body and normal wings

How many map units separate the genes for body colour and wing shape?

Key Concept D: Beyond Mendel

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D2. Polygenic Inheritance

• Polygenic inheritance concerns the inheritance of a characteristic which is controlled by more than one gene. Many conditions are thought to be polygenic, including human skin colour, eye colour, and height. Polygenic inheritance can lead to continuous variation (ex. skin colour in humans)

• Often, variation can also be caused by environmental

factors. Human skin colour is affected by the amount of light (tanning); tallness is controlled by polygenes for skeleton height, but their effect may be retarded by malnutrition, injury, and disease.

Example #1 Eye color in humans is in varying shades of ebony brown to crystal

blue, to Kelly green, and all points in between. Eye color is possibly governed

by 6 or more genes. There are generally 8 different described eye colors.

Basically, dark is dominant at each of the 6 genes. The more dominant alleles

that you have the darker your eyes are.

Assume there are two gene pairs to determine the color of an offspring’s eyes, one that codes for depositing pigment in the front of the iris and one that codes for depositing in the back of the iris. AABB - black/brown Aabb - grey/blue AABb - dark brown aaBB - green AAbb - brown aaBb - dark blue AaBB - brown/green flecks aabb - light blue AaBb - light brown

a) Write the genotype of a light blue-eyed individual. If this child's parents both have two dominant and two recessive alleles, then what is the genotype and phenotype of the parents? b) Which of the phenotypes would be possible if one parent has grey/blue eyes and the other green eyes? c) If one parent has light brown eyes and the other has dark brown eyes, what would be the probability of an offspring with grey/blue eyes? (Express your answer as a whole number percentage)

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Example #2 Human skin color involves the interaction of at least three

independent genes. If we assume that A, B and C will each represent alleles

for dark skin, then a, b and c will represent alleles for light skin. Each person

will have two alleles per gene, so six alleles in total (or more if more than three

genes are involved.

We can symbolize the alleles for darker skin by o and the alleles for

light skin by o . The phenotype of darkest skin would then be caused by

. The phenotype of the lightest skin would be caused by

. If these two produced offspring, they would have the

genotype with an __________________ skin colour.

If both parents have intermediate-coloured skin then the possibilities

of skin colour in the offspring produced would be as shown in the diagram to

the right.

a) On the diagram to the right, indicate the genotypes for the following phenotypes:

very light very dark intermediate

b) What are two possible genotypes for the proportion of the population that are 15/64 and have darker skin? c) What are two possible genotypes for the proportion of the population that are 15/64 and have lighter skin?

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Use the following simplified genotypes for skin color to answer the next questions .

white light medium dark black (albino) Aabb AAbb AaBB AABB aabb aaBb AaBb AABb aaBB Question: State the number or dominant and recessive alleles that must be present/absent for the following phenotypes. The first one is already done for you. dark: 3 dominant alleles and 1 recessive allele

black:

medium:

light:

albino:

Question: Complete the Punnett square for the following cross: light-skinned parent x black-skinned parent. Report the phenotypic probabilities as whole number percentages.

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E1. Constructing a Pedigree

• A pedigree is a graphical representation of the genetic history of an individual or family. The following symbols are used in constructing a pedigree:

E2. Using a pedigree to solve problems Questions 1 through 23 pertain to the inheritance of the earlobe trait in humans that is thought to be controlled by a single gene. There are two general earlobe shapes, free lobes and attached lobes. The allele responsible for free lobes, E, is dominant to the allele for attached lobes, e.

Use the following pedigree to answer questions 1 to 4.

1 2

1 2 3

I

II

note: Affected individuals have the attached earlobe trait.

Carriers (heterozygotes) have not been identified.

1. What is the sex of the oldest child? 2. What is the sex of the youngest child? 3. In what order are the children arranged, from left to right? 4. What must be the genotype of person I-2?

Using a different pedigree of the same family at a later time shows three generations. Use it to answer questions 5 through 10.

1 2

1

2 3

I

II

note: Affected individuals have the attached earlobe trait.

Carriers (heterozygotes) have not been identified.

1 4

III

5. Which person is the son-in-law? 6. To whom is the son-in-law married? 7. What is the gender of their child? 8. What must be the genotype of person II-1? 9. What is the genotype of the maternal grandmother of III-1? 10. If the paternal grandmother of III-1 had the EE genotype, what is the genotype

of the paternal grandfather if he had free ear lobes?

Key Concept E: Human Genetic Analysis

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Use the following pedigree to answer questions 11 through 17.

1 2

1

2 3

I

II

note: Affected individuals have the attached earlobe trait.

Carriers (heterozygotes) have not been identified.

1 4

III

E __ee

E __E __eeE __

E __

11. Can an Ee parent and an ee parent have the results shown in generation II? 12. Predict the genotype of person II-3. 13. Predict the genotype of person II-4. 14. Could child II-3 be EE? Explain your answer. 15. Predict the genotype of person III-1. 16. At some time in the future, II-1 and II-2 have ten more children and all have free earlobes. What is most likely genotype of the father? Examine the pedigree below and predict (insofar as possible) the genotypes of

each family member. Then answer questions 17 to 19.

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I

II

III

IV

1 2

1

1

2 3 4

2

note: Carriers have not been identified.

17. How many generations are shown? 18. How many persons have free ear lobes? ____ Attached ear lobes? ____ 19. How many children did the first generation have? Examine the following data obtained about the families of a newly married man and woman.

Man!s Family

man = 24 years old; has free earlobes

Relation Age Phenotype

sister 26 attached

mother 47 free

father 48 free

paternal

grandmother 70 free

paternal

grandfather 77 attached

Woman!s Family

woman = 25 years old; has free earlobes

Relation Age Phenotype

brother 23 free

brother 16 attached

mother 45 free

father 45 free

20. Construct a pedigree from the information provided in the data table. Use all pertinent pedigree symbols and conventions for labelling as described in the data booklet. Place the man’s family on the left side of the chart, and the woman’s pedigree on the right side. 21. Identify the genotypes of all individuals, insofar as possible. 22. Considering what is already known about the genotype of the man, what is the probability that he is a) homozygous recessive b) homozygous dominant c) heterozygous 23. Considering all the genotype possibilities for the man and woman, what is the greatest probability that an offspring will have attached earlobes?

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E3. Modes of Inheritance Summary

1. Autosomal Recessive Traits 1. both males and females are equally affected 2. affected parents produce only affected offspring 3. the trait can skip a generation and then reappear in later

generations 4. unaffected parents can produce affected offspring

Examples include albinism, hair & eye pigmentation, Tay-Sachs 2. Autosomal Dominant Traits

1. both males and females are equally affected 2. affected parents can produce unaffected offspring 3. affected offspring must have one affected parent 4. the trait does not skip a generation and reappear in later

generations 5. unaffected parents can produce affected offspring

Examples include achondroplasia, huntington’s disease 3. Sex-Linked Inheritance X-Linked Recessive

1. it is more common in males than females 2. affected fathers transmit the gene to all daughters but

not to any sons 3. all the sons of an affected mother are affected with the

disorder 4. an affected daughter must have an affected father

Examples include colourblindness, hemophilia X - Linked Dominant

• affected males produce all affected daughters and no affected sons

4. Mitochondrial Inheritance 1. both males and females can be affected 2. only females can transmit to offspring

5. Incomplete dominance

1. both alleles are partially expressed: neither of the two alleles of the same gene can completely conceal the presence of the other

2. a third, intermediate phenotype occurs

Examples include sickle cell anemia, and flower colour in some plants 6. Codominance

• both alleles are fully expressed • expression of both phenotypes at the same time

Examples include roan cattle & horses, blood types 7. Multiple alleles:

• a gene with more than two alleles

Examples include human blood types 8. Polygenic Inheritance

• two or more genes influences the expression of one trait • the result is an array of possible phenotypes called continuous

variation Examples include skin colour, eye colour, height

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Questions: 1. Numerical Response: Identify the pedigrees that best fit one of the following modes of inheritance:

Autosomal recessive Autosomal dominant Mitochondrial X-Linked Recessive

A. B.

2. Make adjustments on pedigree A and pedigree D to correctly represent carriers. 3. Why are the heterozygotes in pedigree B not indicated as half-shaded?

C.

D.