non-mendelian genetics:

Non-Mendelian Genetics:

Vocabulary Terms…89. Pedigree

90. Sex-linked trait

91. Polygenic trait

92. Incomplete dominance

93. Codominance

94. Multiple alleles

95. mutation

Read 171-180

Chromosomes and Human Genetics

I. Human ChromosomesA. Types

1. Sex Chromosomes – 1 pair – carry the genes that determine male and female features (also some non-sex traits)

1. X and Y do not look alike but behave as a homologous pair at meiosis

2. XX = female, XY = male

2. Autosomes – non-sex chromosomes (22 pairs) – genes are unrelated to sex determination

B. Determining Sex…

X X

X

Y

MOM

DAD

X X X X

X Y X Y

II. Gene Location

A. Linked – Linkage Groups – genes located so close together on a chromosome that the traits always seem to appear together

Ex. Red hair and freckles

Ex. Colorblindness and Hemophilia

X X

B. Sex-linked Traits – genes on the sex chromosomes

- Expression of certain genes often appears more in one sex than the other

- Males require only one copy of a gene since they only have one X chromosome

- See Royal Families of Europe Pedigree- Ex. Eye color in fruit flies, hemophilia, color-

blindness

Colorblindness Tests

X-Linked/Sex Linkage – do not write

• Genes present on the X chromosome exhibit unique patterns of inheritance due to the presence of only one X chromosome in males.

• X-linked disorders show up rarely in females

• X linked disorders show up in males whose mothers were carriers (heterozygotes)

Practice Sex-linked Problems….• What will the result of mating between a

normal (non-carrier) female and a hemophiliac male?

• A female carrier who is heterozygous for the recessive, sex-linked trait causing red-green colorblindness, marries a normal male. What proportions of their MALE progeny will have red-green colorblindness?

• Hemophilia is inherited as an X-linked recessive. A woman has a brother with this defect and a mother and father who are phenotypically normal. What is the probability that this woman will be a carrier if she herself is phenotypically normal?

• Hemophilia is inherited as an X-linked recessive. • A man with Hemophilia has several children with a

woman who has a normal phenotype and is NOT a carrier. What % of the children have hemophilia? What % are carriers?

C. Gene Interactions

1. Polygenetic trait – many genes influence a single trait (ex. Height, intelligence)

2. Pleiotropic effect – one gene having many effects (ex. Gene to make testosterone)

Pleiotropy• Expression of a single

gene has multiple phenotypic effects

• Marfan Syndrome – abnormal gene that makes fibrillin (important in connective tissues)

?

III. Genetic Analysis

A. Karyotype – visualized chromosomes stained, squashed, and photographed at metaphase

- They are characteristic of the species or individual

B. Pedigree – chart showing family relationships (see worksheet)

Pedigree Analysis

• Method of tracking a trait through generations within a family.

• Good method of tracking sex-linked traits as well as autosomal traits.

Sex-Linked Pedigree

• Shows gender bias with males exhibiting the trait more often than females

Autosomal Dominant Pedigree

• Autosomal dominant traits do not skip a generation

• Autosomal dominant traits do not show gender bias

Autosomal Recessive Pedigree

• Autosomal recessive traits skip a generation

• Autosomal recessive traits do not show gender bias

IV. Non-Mendelian Genetics

1. Incomplete Dominance – blended inheritance

- Neither form of the gene is able to mask the other

- Ex. Snap dragon petal color- R1R1 – RED- R1R2 – PINK- R2R2 - WHITE

Incomplete Dominance

• Neither allele is dominant

• Heterozygotes are a blend of homozygous phenotypes = no distinct expression of either allele

Try these• In a plant species, if the B1 allele (blue flowers)

and the B2 allele (white flowers) are incompletely dominant (B1 B2 is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-flowered plant?

•What would be the phenotypic ratio of the flowers produced by a cross between two light blue flowers?

2. Codominance

• No dominance and both alleles are completely expressed

• Ex. Cat color

• C1C1 – Tan

• C1C2 – Tabby (black and tan spotted)

• C2C2 - Black

Try These1. Cattle can be red (RR = all red hairs), white

(WW = all white hairs), or roan (RW = red & white hairs together.

a. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.

b. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

1. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together).

a. What pattern of inheritance does this illustrate?

b. What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

3. Multiple Alleles

• More than 2 alleles for one trait

• Ex. Eye color, hair color, blood type, guinea pig fur color

• ABO blood groups – Each individual is A, B, AB, or O phenotype – Phenotype controlled by marker on RBC– IA and IB alleles are dominant to the i allele – IA and IB alleles are codominant to each

other

Blood Types

Blood Type:

• A

• B

• AB

• O

Genotype

• IAIA , IAi

• IBIB , IBi

• IAIB

• ii

Try These1. If a male is homozygous for blood type B

and a female is heterozygous for blood type A, what are the possible blood types in the offspring?

2) Is it possible for a child with Type O blood to be born to a mother who is type AB? Why or why not?

3. A child is type AB. His biological mother is also type AB. What are the possible phenotypes of his biological father?

Human hair color follows a similar pattern:

Alleles: HBn = brown HBd = blonde hR = red hbk = black

HBnHBn = dark brownHBnHBd = sandy brownHBnhR = auburnHBnhbk = dark brown

HBdHBd = blondeHBdhR = strawberry blondeHBdhbk = blonde

hRhR = redhRhbk = red

hbkhbk = black

Dominant does NOT mean frequent! Recessive can be common!

V. Genetic Conditions

1. Genetic Abnormality – rare condition with little or no ill effects

- Ex. Six fingers, albino, colorblindness

2. Genetic Disorders

• Inherited condition that results in a medical problem

- Ex. Huntington’s Disease, Sickle Cell Anemia, Hemophilia, Muscular Dystrophy

3. Genetic Disease

• A genetic condition that makes the individual susceptible to infection (bacterial or viral)

- Ex. Cystic fibrosis, Down syndrome, SCID (severe combined immunodeficiency disease = bubble boy)

VI. Mutations

• Definition – any change in the DNA

• Possible outcomes: good, bad, or no effect

• Location:– Somatic Cell (body cell) – can lead to cancer– Sex Cell – reproductive organ effecting

gametes

Observed vs. Expected Ratios

• Observed Ratio – what you actually get from two organisms having offspring – all girls

• Expected Ratio – based on your punnett square results – what you would expect to get – half girls and half boys

• Example – using dice

Human Genetics Test Topics

• Sex-linked Traits• Incomplete Dominance/ Codominance• Multiple Alleles (blood typing problems)• Genetic Conditions• Sex Chromosomes vs. Autosomes• Pedigrees/Karyotypes• Observed vs. Expected Ratios• LOTS OF GENETICS PROBLEMS – SHOW

WORK!!!

Human Genetics Test Review Questions:

My daughter is type A, my grandson is type B. What are the blood type(s) that the father would have to be in order for my grandson to be type B?

Red-green color blindness is X-linked in humans.

If a male is red-green color blind, and both parents have normal color vision, which of the male's grandparents is most likely to be red-green color blind?

• A. maternal grandmother

• B. maternal grandfather

• C. paternal grandmother

• D. paternal grandfather

• E. either grandfather is equally likely

1. Suppose a child is of blood type A and the mother is of type 0. What type or types may the father belong to?

Suppose a father and mother claim they have been given the wrong baby at the hospital. Both parents are blood type A. The baby they have been given is blood type O. What evidence bearing on this case does this fact have?

Hemophilia is a sex-linked recessive trait. Cross a hemophiliac female with a normal male. Of all their offspring, what is the probability they will produce a hemophiliac daughter? (H = normal blood, h = hemophilia)

A man with Type A blood marries a woman with Type B blood. They have a type O child. What is the probability of their 15th child having type O blood?

A man whose father is type B and whose mother is type A, has a blood type of A. He marries a type A woman, whose parents had the same blood types as his parents. What are the genotypes of the man and the woman and what is the probability that their first child will be blood type A?

Coat color in cats is a codominant trait. Cats can be black, yellow or calico. A calico cat has black and yellow splotches. In order to be calico. the cat must have an allele for the black color and an allele for the yellow color. Show a cross between a calico cat and a yellow cat. What are the possible genotypes and phenotypes of the offspring?

A mother and father with normal color vision produce six male children, two of whom exhibit red-green colorblindness. Their five female children exhibit normal color vision. Ignoring the fact that these parents ought to seek some family planning advice, explain the inheritance of red-green colorblindness in their male children.

Parents Blood Types Baby Blood type

Mr. Hartzel O    

Mrs. Hartzel

A Jennifer O

Mr. Simon AB Rebecca A

Mrs. Simon AB Holly B

Mr. Peach O

Mrs. Peach O

A nurse at a hospital removed the wrist tags of three babies in the maternity ward. She needs to figure out which baby belongs to which parents, so she checks their blood types. Using the chart below, match the baby to its correct parents. Show the crosses to prove your choices