Distinguish between alleles for incomplete dominance and codominance. Section Objectives: Explain...

• Distinguish between alleles for incomplete dominance and codominance.

Section Objectives:

• Explain the patterns of multiple allelic and polygenic inheritance.

• Analyze the pattern of sex-linked inheritance.

• Summarize how internal and external environments affect gene expression.

What You’ll Learn

You will compare the inheritance of recessive and dominant traits in humans.You will analyze the inheritance patterns of traits with incomplete dominance and codominance.You will determine the inheritance of sex-linked traits.

TelemeresTelomeres have been

compared with the plastic

tips on shoelaces because

they prevent chromosome

ends from fraying and

sticking to each other, which

would scramble an

organism's genetic

information to cause cancer,

other diseases or

death.

Yet, each time a cell divides,

the telomeres get shorter.

When they get too short, the

cell no longer can divide and

becomes inactive or

"senescent" or dies. This

process is associated with

aging, cancer and a higher

risk of death. So telomeres

also have been compared

with a bomb fuse.

Complex Patterns of InheritanceComplex Patterns of Inheritance

• Patterns of inheritance that are explained by Mendel’s experiments are often referred to as simple.

• However, many inheritance patterns are more complex than those studied by Mendel.

Exceptions to Simple Mendelian Genetics

• incomplete dominance-

• neither gene is dominant

• results in a new trait-Heterozygous- mix

• -ex. red X white = pink

• co-dominance- sickle-cell disease.

• Both alleles expressed equally

• Heterozygous- both traits are seen

• ex. black X white = checkered or spotted.

Test to determine possible phenotypes

• The change in shape occurs in the body’s narrow capillaries after the hemoglobin delivers oxygen to the cells.

Sickle-cell disease-codominance

Normal red blood cell

Sickle cell

•Abnormally shaped blood cells, slow blood flow, block small vessels, and result in tissue damage and pain.

•Individuals who are heterozygous for the allele produce both normal and sickled hemoglobin, an example of.

Cause- the oxygen-carrying protein hemoglobin differs by one amino acid from normal hemoglobin.

Cross RR’ X RR’ and Predict offspring probability

Individuals who are heterozygous are said to have the sickle-cell trait because they can show some signs of sickle-cell-related disorders if the availability of oxygen is reduced.

Polygenic Inheritance

• A group of alleles act together for one trait

• Height, & eye color• Fingerprints!• Controlled by

multiple genes• All are different!

• Because of embryonic development- even identical twins have different fingerprints

• Although many of your traits were inherited through simple Mendelian patterns or through multiple alleles, many other human traits are determined by polygenic inheritance.

• In the early 1900s, the idea that polygenic inheritance occurs in humans was first tested using data collected on skin color.

• Scientists found that when light-skinned people mate with dark-skinned people, their offspring have intermediate skin colors.

Skin color: A polygenic trait

• This graph shows the expected distribution of human skin color if controlled by one, three, or four genes.

Skin color: A polygenic trait

Number of Genes Involved in Skin Color

Observed distribution of skin color

Expected distribution- 1 gene

Expected distribution- 4 genes

Expected distribution- 3 genes

Range of skin colorLight Right

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• Polygenic inheritance is the inheritance pattern of a trait that is controlled by two or more genes.

• The genes may be on the same chromosome or on different chromosomes, and each gene may have two or more alleles.• Uppercase and lowercase letters are used to represent the alleles.

Polygenic inheritancePolygenic inheritance


• However, the allele represented by an uppercase letter is not dominant. All heterozygotes are intermediate in phenotype.

• In polygenic inheritance, each allele represented by an uppercase letter contributes a small, but equal, portion to the trait being expressed.

• The result is that the phenotypes usually show a continuous range of variability from the minimum value of the trait to the maximum value.


Multiple phenotypes from multiple alleles

Traits controlled by more than two alleles (a single pair of genes) have multiple alleles.

These alleles may exhibit classic dominance, they may mask each other, they may add to or subtract from each other, or some combination of these effects. Adding one or more alleles to the equation exponentially increases the number of possible expressions for a gene.

Example 1: Human Blood Type

Example 2: Human Hair Color

What is the difference between the polygenic inheritance pattern and multiple alleles?

• Polygenic inheritance pattern refers to many--poly--genes. It describes a trait that is the result of a combination of

proteins from genes on different locations within a chromosome or on chromosomes that are not homologous,

meaning not paired. The gene on one chromosome pair contributes part of the trait, and the genes on other pairs

contribute other components.

• Eye color is a good example of the polygenic inheritance pattern. The appearance of the eye results from flecks

of colors, each resulting from the action of a different gene pair.

• The polygenic inheritance pattern is also responsible for height, skin color, and hair color, among others.

• Keep in mind that each of these genes still has the possibility of having two recessive alleles, two dominant, or

one of each, or the alleles can be incompletely dominant. Because of the numerous combinations, there is a

range of phenotypes, not just two or three, as in a single gene. With a single gene pair, there is an either/or

situation; the characteristics are discontinuous, or distinct from each other.

• There are many heights to which humans grow; There is a range of skin colors, not just chocolate or vanilla; the

same applies to weight, hair color and texture, foot size, and some genetic disorders.

• When two individuals at opposite ends of the continuum mate, the probability is greatest that the offspring's

characteristic will be intermediate. If the different phenotype frequencies are graphed, their distribution resembles

a bell curve

Alleles refer to different versions of the same gene.

• A single gene can have multiple alleles.

•

• Contrast• difference is multiple alleles refers to different versions

of one gene and polygenic traits refers to a single trait which is controlled by multiple genes (each with multiple alleles). Polygenic traits don't follow patterns of mendelian inheritance

Multiple Alleles Govern Blood Type

Human Blood Types

lA lA or lAlilB lB or lBilA lB

ii

Genotypes Surface Molecules Phenotypes

AB

A and BNone

ABABO

Determining blood type is necessary before a person can receive a blood transfusion because the red blood cells of incompatible blood types could clump together, causing death. Your immune system recognizes the red blood cells as belonging to you. If cells with a different surface molecule enter your body, your immune system will attack them.

Blood type

• Blood factors- • A & B- both are

dominant• O is the absence

of either A or B

• Genotypes possible

• AA, AO, BB, BO, AB, OO

• Phenotypes A, B, AB & O

• A person has two alleles. May be:• - two A antigen (blood type A) • - two B antigen (blood type B)• - one each of A and B antigens

(blood type AB)• - or the O antigen (blood type

O)

• Human blood types can be• type A (IAIA or IA i)• type B (IBIB or IBi)• type AB (IAIB)• or type 0 (ii).

• The lA allele is dominant to i, so inheriting either the lAi alleles or the lA lA alleles from both parents will give you type A blood.

Phenotype A

• Surface molecule A is produced.

Surface molecule A

• The lB allele is also dominant to i.

Phenotype B

• To have type B blood, you must inherit the lB allele from one parent and either another lB allele or the i allele from the other.

• Surface molecule B is produced.

Surface molecule B

• The lA and lB alleles are codominant.

Phenotype AB

• This means that if you inherit the lA allele from one parent and the lB allele from the other, your red blood cells will produce both surface molecules and you will have type AB blood.

Surface molecule B

Surface molecule A

• The i allele is recessive and produces no surface molecules.

Phenotype O

• Therefore, if you are homozygous ii, your blood cells have no surface molecules and you have blood type O.

Blood Types

• Can AB X O have a type O child? Explain

• Cross the following

Using a Punnett square.

What possible offspring can they have?

• A X B =__________

• O X A =__________

• AB X O = ________

Hospital Mix-up• 3 babies have lost their bands in the hospital

• Match the babies to the correct parents

• A Baby - O• B Baby - B• C Baby - AB

Couples blood types

1 2 3

Mothers’ AO AO AB

Fathers OO BO OO

Rh negative-problem

• Mother Rh -, Father Rh+, Fetus Rh+

• mother may build up antibodies that may cross the placenta to destroy the babies RBC.

• The more pregnancies- the more antibodies

• mother given a rhogram shot to stop the antibody build up

Environmental InfluencesEnvironmental Influences

• The genetic makeup of an organism at fertilization determines only the organism’s potential to develop and function.

• As the organism develops, many factors can influence how the gene is expressed, or even whether the gene is expressed at all.

• Two such influences are the organism’s external and internal environments.

• Temperature, nutrition, light, chemicals, and infectious agents all can influence gene expression.

Influence of external environmentInfluence of external environment


• In arctic foxes temperature has an effect on the expression of coat color.

• External influences can also be seen in leaves. Leaves can have different sizes, thicknesses, and shapes depending on the amount of light they receive.


Influence of internal environmentInfluence of internal environment• The internal

environments of males and females are different because of hormones and structural differences.

• An organism’s age can also affect gene function.

• Many human traits are determined by genes that are carried on the sex chromosomes; most of these genes are located on the X chromosome.

Sex-Linked Traits in Humans

• The pattern of sex-linked inheritance is explained by the fact that males, who are XY, pass an X chromosome to each daughter and a Y chromosome to each son.

• Females, who are XX, pass one of their X chromosomes to each child.


Male Female

Sperm Eggs

FemaleFemale MaleMale

Female Male

MaleMaleFemale Female

Eggs Sperm

• If a son receives an X chromosome with a recessive allele, the recessive phenotype will be expressed because he does not inherit on the Y chromosome from his father a dominant allele that would mask the expression of the recessive allele.


• Two traits that are governed by X-linked recessive inheritance in humans are red-green color blindness and hemophilia.

• People who have red-green color blindness can’t differentiate these two colors. Color blindness is caused by the inheritance of a recessive allele at either of two gene sites on the X chromosome.

Red-green color blindness

• Hemophilia A is an X-linked disorder that causes a problem with

blood clotting.

• About one male in every 10 000 has hemophilia, but only about one in

100 million females inherits the same disorder.

• Males inherit the allele for hemophilia on the X chromosome from

their carrier mothers.

• One recessive allele for hemophilia will cause the disorder in males.

Females would need two recessive alleles to inherit hemophilia.

Hemophilia: An X-linked disorder

• What would happen if an entire chromosome or part of a chromosome were missing from the complete set?

Changes in Chromosome Numbers

• As you have learned, abnormal numbers of chromosomes in offspring usually, but not always, result from accidents of meiosis.

• Many abnormal phenotypic effects result from such mistakes.

• Humans who have an extra whole or partial autosome are trisomic—that is, they have three of a particular autosomal chromosome instead of just two. In other words, they have 47 chromosomes.

Abnormal numbers of autosomes

• To identify an abnormal number of chromosomes, a sample of cells is obtained from an individual or from a fetus.

A pedigree- graphic representation of genetic inheritance

• No shade-no characteristic

• Shaded areas indicate the disease

• 1/2 is a carrier• male-square• girl-circle• vert. Line-connects

parent w/offspring• horiz.= connects

parents

-used to show inheritance of certain conditions in a family

Pedigrees illustrate

inheritance

Pedigrees illustrate

inheritance

Male

Female

Affected male

Affected female

Mating

Parents

Siblings

Known heterozygotes for recessive allele (Carriers)

Death

• In a pedigree, a circle represents a female; a square represents a male.

Pedigrees illustrate inheritance

Pedigrees illustrate inheritance

Female Male

?

I

II

III

IV

1 2

1

1

1

32

2

2

4

3

3

5

4

4 5

Can be used to trace an inherited illness

Exp- Student observations`

• Students must agree to be “tested” for an experiment.

• Develop your own exp to observe traits in your group. Can be hands, hair, eyes…

• Write your problem and hypothesis before you plan your exp.

• Pg. 136

What traits in class are most common?

Trait Dominant Recessive

Skin color

Extra fingers or toes

Freckles

Earlobe

Tongue rolling

Widow’s peak

Chin shape

What traits are most common?

Trait Dominant Recessive

Skin color Dark

Extra fingers or toes

6 or more

Freckles Freckles

Earlobe Free

Tongue rolling Roll edges

Widow’s peak Pointed

Chin shape indented

Genetically Inherited Human Disorders:

Autosomal recessive disorders:

• Parents can be carriers & not have disease• Show up only in the homozygous recessive

person (aa) who inherits a recessive allele from both parents, who were carriers (Aa xAa).

• (25% chance of this happening)

Simple Recessive HereditySimple Recessive Heredity

• Most genetic disorders are caused by recessive alleles.

Cystic fibrosisCystic fibrosis

• Cystic fibrosis (CF) is a fairly common genetic disorder among white Americans.

Cystic fibrosisCystic fibrosis

• Approximately one in 28 white Americans carries the recessive allele, and one in 2500 children born to white Americans inherits the disorder.

• Due to a defective protein in the plasma membrane, cystic fibrosis results in the formation and accumulation of thick mucus in the lungs and digestive tract.


Cystic fibrosis:

• Homozygous recessives (cc)

• carriers- 1/20 white• Diet, antibiotics and

treatment can extend life to 25 years or more.

• body cannot make needed chloride channel, high concentrations of extra-cellular chloride

• causes mucous to build up, infections, pneumonia.

http://www.ccff.ca/~cfwww/brochure/child.htm

Tay-Sachs diseaseTay-Sachs disease

• Tay-Sachs (tay saks) disease is a recessive disorder of the central nervous system.

• In this disorder, a recessive allele results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the central nervous system.

• Because this lipid fails to break down properly, it accumulates in the cells.

I

II

III

IV

Typical Pedigree for

Typical Pedigree for 1 2

1

1

1

32

2

4

3

Tay-SachsTay-Sachs


Sickle-cell disease• The most

common inherited disease of African-Americans (1:400 affected).

• Homozygous recessives (ss) make abnormal form of hemoglobin that deforms red blood cells and causes a cascade of symptoms

• (clogging of blood vessels, organ damage, kidney failure).

http://noah.cuny.edu/pregnancy/march_of_dimes/birth_defects/siklcell.html

• Phenylketonuria (fen ul kee tun YOO ree uh), also called (PKU), is a recessive disorder that results from the absence of an enzyme that converts one amino acid, phenylalanine, to a different amino acid, tyrosine.

• Because phenylalanine cannot be broken down, it and its by-products accumulate in the body and result in severe damage to the central nervous system.

PhenylketonuriaPhenylketonuria

• A PKU test is normally performed on all infants a few days after birth.

• Infants affected by PKU are given a diet that is low in phenylalanine until their brains are fully developed.

• Ironically, the success of treating phenylketonuria infants has resulted in a new problem.


• If a female who is homozygous recessive for PKU becomes pregnant, the high phenylalanine levels in her blood can damage her fetus—the developing baby.

• This problem occurs even if the fetus is heterozygous and would be phenotypically normal.



Phenylketonurics: Contains Phenylalanine

Simple Dominant HereditySimple Dominant Heredity

• Remember that in Mendelian inheritance, a single dominant allele inherited from one parent is all that is needed for a person to show the dominant trait.

• Many traits are inherited just as the rule of dominance predicts.

Simple dominant traitsSimple dominant traits• A cleft chin, widow’s

peak hairline, hitchhiker’s thumb, almond shaped eyes, thick lips, and the presence of hair on the middle section of your fingers all are examples of dominant traits.

Huntington’s diseaseHuntington’s disease

• Huntington’s disease is a lethal genetic disorder caused by a rare dominant allele.

• It results in a breakdown of certain areas of the brain.

Huntington’s diseaseHuntington’s disease

• Ordinarily, a dominant allele with such severe effects would result in death before the affected individual could have children and pass the allele on to the next generation.

• But because the onset of Huntington’s disease usually occurs between the ages of 30 and 50, an individual may already have had children before knowing whether he or she is affected.

• Interpret a pedigree.

Section Objectives:

• Identify human genetic disorders caused by inherited recessive alleles.

• Predict how a human trait can be determined by a simple dominant allele.

Typical Pedigree of Huntington’s DiseaseTypical Pedigree of Huntington’s DiseaseI

1

II

III

2

1

1

3

2

2 4

3 4 5

5

I

II

III

IV

1 2

1

1

1

32

2

4

3

Question 1

What does this pedigree tell you about those who show the recessive phenotype for the disease?

I

II

III

IV

1 2

1

1

1

32

2

4

3

The pedigree indicates that showing the recessive phenotype for the disease is fatal.

http://www.google.com/imgres?q=punnett+square+codominance&start=326&hl=en&safe=active&sa=X&tbo=d&rls=com.microsoft:en-us&rlz=1I7RNSN_enUS409&biw=1366&bih=587&tbm=isch&tbnid=Xpv-vMjoipvjVM:&imgrefurl=http://clip.suabnag.com/%3Fw

%3DP1msG5fOQ6g&docid=0TCz7n2UBqAY6M&imgurl=http://i.ytimg.com/vi/o0Cl7I3KSGs/mqdefault.jpg&w=320&h=180&ei=OaIiUaKpAs2vqAHV9YDQBg&zoom=1&iact=hc&vpx=1064&vpy=200&dur=47&hovh=144&hovw=256&tx=52&ty=61&sig=115044282234707208

727&page=12&tbnh=144&tbnw=256&ndsp=32&ved=1t:429,r:33,s:300,i:103&surl=1

Question 2

What must happen for a person to show a recessive phenotype?

Answer

The person must inherit a recessive allele for the trait from both parents.

Autosomal dominant disorders

• Polydactyl• (extra fingers or toes): • PP or Pp = extra digits, • aa = 5 digits. • 98% of all people in

the world are homozygous recessive (pp).

Sex- A genetic trait

• The 23rd pair of chromosomes determine sex

• Male= XY & Female = XX

• each time fertilization occurs, there is a 50/50 chance the offspring will be maleThe MALE determines a baby’s sex

• Autosomes- all chromosomes except for the sex chromosomes

• Autosomes for males & females are the same

Sex chromosomes

• Weird Info• A platypus has 10

sex chromosomes

• Sex can be chosen• Ex. X is larger- use

filter

TwinsFraternal vs. Identical

Sex-linked

• Certain genes on the X chromosome are missing from the Y chromosome

• In humans the diploid number of chromosomes is 46, or 23 pairs.

• There are 22 pairs of homologous chromosomes called autosomes. Homologous autosomes look alike.

• The 23rd pair of chromosomes differs in males and females.

Sex determinationSex determination

• These two chromosomes, which determine the sex of an individual, are called sex chromosomes and are indicated by the letters X and Y.


Sex determinationSex determination• If you are female,

your 23rd pair of chromosomes are homologous, XX.

• If you are male, your 23rd pair of chromosomes XY, look different.

X X

Female

YX

Male

• Males usually have one X and one Y chromosome and produce two kinds of gametes, X and Y.

• Females usually have two X chromosomes and produce only X gametes.

• It is the male gamete that determines the sex of the offspring.



XX Female

XY Male

X

X

X Y

XX Female

XY Male

XX Female

XY Male

• Traits controlled by genes located on sex chromosomes are called sex-linked traits.

• The alleles for sex-linked traits are written as superscripts of the X or Y chromosomes.

• Because the X and Y chromosomes are not homologous, the Y chromosome has no corresponding allele to one on the X chromosome and no superscript is used.

Sex-linked inheritanceSex-linked inheritance

• Also remember that any recessive allele on the X chromosome of a male will not be masked by a corresponding dominant allele on the Y chromosome.


Females:

Males:1/2 red eyed1/2 white eyed

all red eyed

White-eyed male (XrY)

Red-eyed female (XRXR)

F1 All red eyed

F2



• The genes that govern sex-linked traits follow the inheritance pattern of the sex chromosome on which they are found.

Click here to view movie.

sex-linked traits

• traits are determined by genes carried on sex chromosomes

• If a trait is X linked,

• males pass it to all their daughters

• and none of their sons.

• The mother has a 50/50 chance of passing it on to each child

• If the son receives a recessive X from the mom, he will express the recessive phenotype b/c no dominant allele is available from the father.

• If the father- the dominant characteristic would hide it

sex-linked traits

• Determined by alleles carried only on the x chromosome-

• Ex. Colorblindness &

• Hemophilia (bleeding disease)

color blindness -on X chromosomes- can’t distinguish between some colors;

• red and green

• has no allele on the Y chromosome

sex-linked traits

• Female- Xx- 1 recessive with the trait is dominated by the normal and no disease shows up

• female xx- 2 recessive w. disease shows up

• If the recessive X-linked trait is inherited it shows up- XY-shows up

Genetic Disorders & sex chromosomes

• Hemophilia• Free bleeders

disease• A recessive trait• Males get it more

frequently• Females must get

the gene from both parents

• Dyslexia• - a genetic disorder

that is also called word blindness

• Caused by dominant gene

• See & write words backwards

CYU 27.2

• What is incomplete dominance?• Neither gene is totally dominant over the

other• What 2 gene combinations can a person with

type A blood have?• AO or AA• Why are there more color blind males than

females?• Recessive traits on X always show up

• Metaphase chromosomes are photographed; the chromosome pictures are then enlarged and arranged in pairs by a computer according to length and location of the centromere.


• This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome numbers in cells.


• Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood.

Down syndrome: Trisomy 21

• It occurs in about one in 700 live births.

• Down syndrome is a group of symptoms that results from trisomy of chromosome 21.

Down syndrome: Trisomy 21

• Individuals who have Down syndrome have at least some degree of mental retardation.

• The incidence of Down syndrome births is higher in older mothers, especially those over 40.

• Many abnormalities in the number of sex chromosomes are known to exist.

Abnormal numbers of sex chromosomes

• An X chromosome may be missing (designated as XO) or there may be an extra one (XXX or XXY). There may also be an extra Y chromosome (XYY).

• Any individual with at least one Y chromosome is a male, and any individual without a Y chromosome is a female.

Abnormal numbers of sex chromosomes

• Most of these individuals lead normal lives, but they cannot have children and some have varying degrees of mental retardation.

27.3 Genetic Disorders

• Nondisjunction• About 200 genetic

disorders controlled by X chromosome

produces 1 cell with an extra chromosome & one cell lacking a chromosome

Use an O for the missing

Ex. XOSome Disorders can be

prevented if couple has only girls

• Would you choose the sex?

PKU

• Genetic disorder in which some chemicals in the body do not break down as thy should

• Chemicals can damage brain cells

• Today- children tested at birth

• Can be controlled with diet & can grow normally

nondisjunction

• The frequency of nondisjunction is quite high in humans, but the results are usually so devastating to the growing zygote that miscarriage occurs very early in the pregnancy.

• If the individual survives, he or she usually has a set of symptoms –

• a syndrome - caused by the abnormal dose of each gene product from that chromosome.

Syndromes

• Chromosomes missing

• XO – female• YO- fetus dies

• An XO female & XXY male cannot make sex cells but they can live

• Extra chromosome

• XXY- male• 3 of the 21st

chromosome causes Down’s Syndrome (Trisomy 21)

Human disordersdue to chromosome alterations in autosomes

A. Down syndromecharacteristic facial

features, short stature; heart defects

• susceptibility to respiratory disease, shorter lifespan

• prone to developing early Alzheimer's and leukemia

• often sexually underdeveloped and sterile, mental retardation

http://genome6.ped-gen.uiowa.edu/cgi-bin/M1GeneticsDispatch?Message=Browser&Path=Supplements

http://www.nas.com/downsyn/

Optical Illusions

Which of the following inherited diseases would a black American be most likely to inherit?

Question 1

D. sickle-cell disease

C. phenylketonuria

B. Tay-Sachs disease

A. cystic fibrosis

The answer is D.

Trisomy usually results from _______.

Question 2

D. twenty-two pairs of chromosomes

C. nondisjunction

B. incomplete dominance

A. polygenic inheritance

The answer is C.

How do red blood cells of phenotype O differ from the cells of the other phenotypes?

Question 3

Answer

Red blood cells of phenotype O display no surface molecules.

• A pedigree is a family tree of inheritance.

Mendelian Inheritance of Human Traits

• Most human genetic disorders are inherited as rare recessive alleles, but a few are inherited as dominant alleles.

• Some alleles can be expressed as incomplete dominance or codominance.

When Heredity Follows Different Rules

• There may be many alleles for one trait or many genes that interact to produce a trait.

• Cells have matching pairs of homologous chromosomes called autosomes.

• Sex chromosomes contain genes that determine the sex of an individual.

• Inheritance patterns of genes located on sex chromosomes are due to differences in the number and kind of sex chromosomes in males and in females.

When Heredity Follows Different Rules

• The expression of some traits is affected by the internal and external environments of the organism.

• Sex-linked traits are determined by inheritance of sex chromosomes. X-linked traits are usually passed from carrier females to their male offspring. Y-linked traits are passed only from male to male.

Complex Inheritance of Human Traits

• The majority of human traits are controlled by multiple alleles or by polygenic inheritance. The inheritance patterns of these traits are highly variable.

• A karyotype can identify unusual numbers of chromosomes in an individual.

Complex Inheritance of Human Traits

• Nondisjunction may result in an abnormal number of chromosomes. Abnormal numbers of autosomes usually are lethal.

Why is genetics important?

• Genes govern the traits of all animals and plants

• Identify genetic disorders to help control them by diet or take preventive measures

• Help identify couples that may pass on hereditary disease

• Also- may be used in repairing damaged areas in the body in the future.

Genetic Counseling

• Traits run in families• Counselor can help answer questions• How did their baby get the disorder?• If the baby is health, does it have a problem

gene?• Is the trait dominant or recessive?• What will happen to the baby’s health as it

gets older?• What are the chances that future children will

have the trait?

Genetic counselors can ID disease risk

• What problems would you have if your culture valued boys over girls and only boys were born for 10 years?

• Should insurance companies pay medical costs of couples who cannot afford to pay for determining the sex?

Amniocentesis • Cells from Fluid are

grown in a nutrient solution for 10 days- growing

• Using a microscope, the chromosomes are photographed

• Cut out, match them in pairs

• Place on chart• ID # & make sure that

there are the correct #• New- Placenta test

Karyotype

Karyotyping

• Cells (from blood, amniotic fluid, etc) are grown in vitro to increase their number

• Cell division is then arrested in metaphase with colchicine (prevents mitotic spindle from forming)

• Cells are centrifuged and lysed to release chromosomes

• Chromosomes are stained, photographed, and grouped by size and banding patterns

• Can help;• in genetic counseling about

diseases.• ID parents• ID genetic disease

characterized by the wrong number of chromosomes– Down’s Syndrome

Normal male

karyotype

Normal female karyotype

IDENTIFY

body chromosomes (autosomes) & Sex chromosomes

Genetic Engineering

• Using biological or chemical means to change the DNA sequence

• Can help diabetics by producing insulin– Goats producing

medicine or spider silk

Improve crops• Grow more than one

crop a year• Smaller plants, more

grain• Frost free

strawberries

Review

• Describe 2 genetic disorders

• Why are males more likely to have some genetic diseases?

• Describe the importance of genetic engineering

Human Genome Project

• Human Genome Project Goal: sequencing all DNA on all the human chromosomes

• Genome- chart showing the location of individual genes for human traits on a chromosome

• Used to ID genes responsible for specific traits

• more than 75 000 genes on the 46 chromosomes

• Over 3000 genetic disorders (inherited)

• Potential- • ID those at risk by

diagnosing disorder and eventually correcting the disorder

• Now• Help control risk w/diet…• Plan on having children if

at risk of problems

DNA sequencing

• DNA can be cut into pieces by enzymes

• Pieces are inserted into bacteria

• DNA reproduced as bacteria reproduces

• DNA fragments put in gel in an electric current

• DNA likes up making a map

• Electrophoresis

New Genetic Technologies

• Stem cell research• May eventually cure

• Paralysis

• Alzheimer's

• Grow new organs

Genetic Disorders

Patterns of Inheritance

When studying human disorders, biologists often construct pedigree charts to show the pattern of inheritance of a characteristic within a family.

The particular pattern indicates the manner in which a characteristic is inherited.

Genetic counselors construct pedigree charts to determine the mode of inheritance of a condition.

Height is a multifactorial trait.

CYU

1. How can an error in meiosis cause a sex cell to have the wrong number of chromosomes?

2. Name 3 genetic disorders and tell how each one of them is controlled by genes.

3. How can a genetic counselor use a pedigree to help families with genetic disorders?

4. Why do you think an XO female can survive but a YO male will die before birth?

EOC 27.1 The role of chromosomes

• Each human sex cell has 23 chromosomes. Each human body cell has 46 chromosomes arranged in pairs

• Amniocentesis is a way to look at the chromosomes of a fetus

• The sex of a person is determined by a pair of sex chromosomes.

• Human females have XX and males have XY

27.2 Human Traits

• If a person has a dominant trait, one or both of the parents will also have the trait.

• If a person has a recessive trait, both of the parents will also carry the gene for the trait.

• Traits in which neither gene is totally dominant over the other show incomplete dominance

• Three genes control blood types in humans but each person has only 2 genes for this trait Males show recessive traits located on the X chromosomes more often than females do.

27.3 Genetic disordersNondisjunction

• If chromosome pairs do not pull apart during meiosis, errors in chromosome number result. Hemophilia, cystic fibrosis, and dyslexia are genetic disorders.

• A genetic counselor uses knowledge of genetics to predict & explain disorders in children

Why doesn’t it always come up with the perfect %?

• What sex chromosome does the mother pass on? Is there any option?

• What sex chromosome does the father pass on?

• Who determines if a boy is born?• What are the chances of having a boy?• If you Flip a coin, how often would you expect to

get heads?• Do you?

Question 1

Which of the following is NOT a sex-linked trait?

D. red-green color blindness

C. male patterned baldness

B. sickle-cell disease

A. hemophilia

The answer is B.

Question 2

Human eye color is determined by _______.

D. polygenic inheritance

C. codominance

B. sex-linked inheritance

A. the influence of hormones

The answer is D.

Question 3

What are blood phenotypes based on?

AnswerBlood phenotypes are based on a molecule that attaches to a membrane protein found on the surface of red blood cells.

Question 4

Cob length in corn is the result of _______.

D. simple dominance

C. polygenic inheritance


A. sex-linked inheritance

The answer is C.

Question 5

A cleft chin is the result of _______.

D. sex-linked inheritance

C. polygenic inheritance


A. simple dominance

The answer is A.

Question 6

What is the difference between simple Mendelian inheritance and inheritance by incomplete dominance?

In Mendelian inheritance, heterozygous individuals will display the inherited dominant trait of the homozygotes. However, when traits are inherited in an incomplete dominance pattern, the phenotype of heterozygous individuals is intermediate between those of the two homozygotes.

Question 7

If a trait is Y-linked, males pass the Y-linked allele to _______ of their daughters.

D. none

C. all

B. half

A. a quarter

The answer is D. Y-linked traits are only passed to males.

Question 8

What is necessary for a person to show a dominant trait?

AnswerThe person must inherit at least a single dominant allele from one parent for the trait to appear.

Question 9

Why is sickle-cell disease considered to be an example of codominant inheritance?

AnswerIndividuals who are heterozygous for the sickle-cell allele produce both normal and sickled hemoglobin. This is an example of codominance.

Question 10

What sex is an XXY individual?

Answer

Any individual with at least one Y chromosome is a male.

Distinguish between alleles for incomplete dominance and codominance. Section Objectives: Explain...

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