Ch. 10.1 Mendel’s Discoveries

Gregor Mendel (1866)• “Father of

Modern Genetics”• Breed pea plant.

(Pre- Mendel: Blending of traits hypothesis)

Background VocabBackground VocabTrue-breeds: pure gene lines –

offspring match parent Self-pollination: pollen from flower

fertilizes the same plantCross-fertilization: pollen will

fertilize a different plantHybrid: Cross between organisms

with different traits (blonde hair & brown hair)

Trait: Physical characteristics

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Cross pollination Cross pollination

6Trait Studied Dominant Form

Recessive Form

F2 Dominant-to- Recessive Ratio

SEED SHAPE

SEED COLOR

POD SHAPE

POD COLOR

FLOWER COLOR

FLOWER POSITION

STEM LENGTH

2.96:1

3.01:1

2.95:1

2.82:1

3.15:1

3.14:1

2.84:1787 tall 277 dwarf

651 long stem 207 at tip

705 purple 224 white

152 yellow428 green

299 wrinkled882 inflated

6,022 yellow 2,001 green

5,474 round 1,850 wrinkled

Mendel’s Experimental designMendel’s Experimental design

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Parental generation (P) White X Purple (truebreed X truebreed)

Offspring: F1 Generation (Hybrids)100% purple

F1 Cross Purple X Purple

(hybrid X hybrid)

Offspring: F2(3:1 – Purple : White)

75% Dominant: 25% Recessive

MendelMendel’’s Conclusions:s Conclusions:Inheritance is determined by chemical

factors (genes) passed from one generation to the next (particulate hypothesis)

Genes can come in more than one form= alleleExample: (white vs purple)

Ch. 10.2 Mendel’s Genetics

More Genetics VocabMore Genetics Vocab• Homozygous: two identical

alleles (AA or aa)• Heterozygous: two different

alleles (Aa)• Phenotype: Physical appearance • Genotype: Genetic make-up

– Homozygous dominant (AA)– Homozygous recessive (aa)– Heterozygous (Aa)

MendelMendel’’s Principless Principles1. There are alternative forms of genes

(alleles)2. There are 2 alleles for each trait (BB,Bb,

bb) * we now know there can be more.3. Some alleles are dominant; some

recessive. 4. Principle of SEGREGATION: Alleles

for each trait segregate (separate) during gamete formation (Anaphase I of meiosis)

Monohybrid Crosses = Parents differ in only 1 trait

P: Purple X White

F1: all purple (100% dominant)F1 purples self- fertilize to see if white trait was lost.

F2: 75% purple; 25% white

(dominant) (recessive)

Diagram that shows all possible outcomes of a genetic cross

Standard Mendelian Cross #1:Standard Mendelian Cross #1:

If purple flower color is dominant, what phenotypes are expected if a purebred purple flowered plant is crossed with a purebred white flowered plant?

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WWWW x wwww

Phenotypic Ratio: 100% purple

Genotypic ratio: 100% Ww

Standard Mendelian Cross #2:Standard Mendelian Cross #2:

If purple flower color is dominant, what genotypes are expected if a heterozygote is crossed with another heterozygote.

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WwWw x WwWw

Phenotypic ratios:

3 purple: 1 white

Genotypic ratios:

1WW:2Ww:1ww

Testcross: Helps determine the genotype of a dominant phenotype

• Dominant phenotype could be AA or Aa

• Unknown Dominant X Recessive (aa)- Any recessive offspring, unknown= Aa- All dominant offspring, unknown= AA

Mendel’s DIHYBRID CROSSES(2 traits)

Independent Assortment: Alleles for different traits do not influence each other’s segregation during meiosis.

List the gamete combinations possible for each of the genotypes listed below:

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RrYY

rrYY

RrYy

RY, rY, RY, rY

rY, rY, rY, and rY

RY, Ry, rY, and ry

Dihybrid Cross

F2: 9:3:3:1 Ratio

Traits are inherited separately.

Black hair is dominant to white

Short hair is dominant to long

Cross a heterozygous black & short haired mouse with a white & heterozygous short haired mouse.

1. What are the genotypes of the parents?

2. What are the genotypic and phenotypic ratios of the F1 generation?

10.3 Exceptions to Mendel

Incomplete/Intermediate dominance: blending of phenotypesneither allele takes a fully dominant role

P1: Red x White flowers

F1: Pink flowers

F2: 1 red: 2 pink: 1 white

Codominance• BOTH alleles are expressed in heterozygotes.• Not incomplete dominance• EX: Roan cattle and Blood types

Multiple AllelesMore than 2 alleles for an inherited character.

Eye colorBlood type: A, B, AB, or O

Fur color

Blood Typing: Multiple Allelism

a) Human blood type is expressed by 3 alleles: IA, IB and i.

b) IA and IB are Co-dominant

c) i is recessive.

Codominance in blood groups

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Blood Type: Codominance & Multiple Alleles

Caucasians African American

Hispanic Asian

O + 37% 47% 53% 39%

O - 8% 4% 4% 1%

A + 33% 24% 29% 27%

A - 7% 2% 2% 0.5%

B + 9% 18% 9% 25%

B - 2% 1% 1% 0.4%

AB + 3% 4% 2% 7%

AB - 1% 0.3% 0.2% 0.1%

• Could a person with Type A blood receive type O blood? Could they receive Type AB?

• Could a person with AB- blood receive AB+?

• List the blood types that type B+ could receive?

Polygenic Inheritance: Multiple Genes affect a trait

Phenotypes of these traits demonstrate continuous continuous variationvariation (bell curve)

Examples: Examples: height, weight, skin color, intelligence.

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Continuous variation in skin Continuous variation in skin color color

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Environmental Influence on Genes

Temperature, pressure, pH, presence of certain chemical compounds influence how genes are expressed.

Epigenetics: study of how genes are influenced by environmental conditions.

Environmental Influence

1. Some flowers colors are influenced by the acidity of the soil (Hydrangea).

1. The color of the arctic fox is influenced by temperature.

2. Siamese cats have darker hair at areas that are cooler than body temperature (ears, nose and paws).

3. Human size is influenced by nutrition.

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10.5: Sex Linked Genes: Genes located on X or Y chromosome

Do you think the X chromosome or the Y chromosome holds more genes?

Rules

1. Recessive Sex Linked Traits:- Affect males more than females - Males only need one copy of the gene (XaY).- Females can be carries (XAXa)

2. Dominant Sex- Linked Traits: - More likely to affect females (XA XA or XA Xa)

Recessive Sex-Linked Disorders Color-blindness Hemophelia Baldness Versions of Muscular Dystrophy

12.3- Pedigrees

A Pedigree is a family tree that shows the inheritance of a genetic disorder

Carriers: do not have the disorder but can pass it on (heterozygous)

A pedigree can allow you to determine whether a trait is autosomal, or sex-linked.

1.1. AutosomalAutosomal disorders affect males and females equally.

1. If the trait is autosomal dominantautosomal dominant, every individual every individual who has the disorder will have at at least one parent least one parent who has the disorder.

2. If the trait is autosomal recessiveautosomal recessive, an individual with the trait can have one, two or neither parentone, two or neither parent exhibit the trait.

1. Sex-linked traits are carried on the X chromosome, and therefore affect one gender or the other in disproportionately high numbers.

a) Sex-linked recessive traits affect males in higher numbers.

• Since they have only one X chromosome, if males receive a single copy of this recessive allele, they will show the phenotype.

• Females must still receive two recessive versions to show the phenotype.

b) Sex-linked dominant traits affect females in higher numbers

• A female has two X chromosomes, and therefore is twice as likely to receive the trait

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Question: Question: Is this disorder autosomal or sex-linked?

Is it dominant or recessive?

Parents are unaffected

Both males and females are affected

Complete the following pedigrees. Which is for a sex-linked trait? How do you know?

Is it a dominant or recessive trait?

Royal Family Pedigree

Human genetic disorders

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10.4 Gene linkage

Genes located on the same chromosome tend to be linked

Loci: location of a gene on a chromosome

• Gene Linkage:

• Gene closer together on chromosome have a greater likelihood of traveling together during crossing over

• Greater likelihood of inheriting genes together

12.1Genome: the complete set of genetic material

12. 4- Genes and Cancer

• Regulation of Cell Cycle– Growth factors: Initiate cell division – Tumor Suppressor Genes: Stop Cell Division

• Cancer is ALWAYS a genetic disease due to mutations in DNA

– Mutation in somatic cells= not passed on to offspring

– If mutation occurs in ovaries or testes• offspring will inherit an abnormal copy of a gene that increases

their likelihood of developing cancer

Epigenetics

NOVA Video (13min)