Non-Mendelian Genetics: Genes that don’t obey Mendel’s laws

2 Types of Human Chromosomes Autosomes- Contain genes that code for traits unrelated to the sex of the individual. Somatic cells (non-sex cells) have 22 pairs (44) of these. All of the genes studied thus far have been on autosomes. Sex Chromosomes- Contain genes that code for the sex of the individual as well as other traits. Somatic cells have 1 pair (2) of these. Male- XY Female- XX

Determining Sex MOM X X X X X X X DAD X Y X Y Y

Sex-Linked Traits X-linked disorders include Hemophilia (bleeding disease) and color-blindness. These are both recessive traits. Males have 1 x sex chromosome; therefore, it only takes that one x to be affected to make the male have a x-linked disease X-linked disorders show up rarely in females because both of the x sex chromosomes must be recessive. Y-linked disorders include male baldness and some forms of infertility. Females cannot have Y-linked disorders.

Click and choose the button For a Flash animation explaining the inheritance of hemophilia go to http://www.dnaftb.org/dnaftb/13/concept/index.html and select the animation button at the bottom of the page.

Colorblindness Tests

Sex-linked Punnett Square Problems 1. Hemophilia is a recessive trait linked to the x sex chromosome. What are the genotypic/phenotypic ratios of a cross between a carrier female and a normal male?

2. Red-green colorblindness is a recessive trait linked to the x sex chromosome. A red-green colorblind female and a normal male have a child. What is the probability (regardless of gender) that it will be red-green colorblind?

3. Muscular Dystrophy is a X-linked recessive trait 3. Muscular Dystrophy is a X-linked recessive trait. A carrier female and a normal male have children. Will any of their children have a chance of having this disorder? If so, list the proportion(s), including the gender(s).

4. A woman has a brother with Hemophilia and a mother and father who are normal. What is the probability that this woman is a carrier if she is normal?

Incomplete Dominance This is when neither form of the gene is able to mask the other. Instead, they phenotypically blend together. An example of this is snapdragon petal color: R1R1 – RED R2R2 - WHITE R1R2 – PINK

In a plant species, if the B1 allele (blue flowers) and the B2 allele (white flowers) are incompletely dominant (B1B2 is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-flowered plant?

Using the information from the previous question, what would be the phenotypic ratio of the flowers produced by a cross between two light blue flowers?

Oompas can have red (H1H1), blue (H2H2), or purple hair (H1H2) Oompas can have red (H1H1), blue (H2H2), or purple hair (H1H2). The allele that controls this is incompletely dominant. A purple haired Oompa marries a blue haired Oompa. What are the phenotypic and genotypic ratios of their offspring?

Codominance Neither allele is dominant and both alleles show up individually in the phenotype. Ex. Cat color TT– Tan TB – Tabby (black and tan spotted) BB - Black

Cattle can be red (RR = all red hairs), white Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together. Predict the phenotypic ratios of offspring when a white cow is crossed with a roan bull.

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

A cross between a black cat & a tan cat produces A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). What is the phenotypic ratio of kittens if a tabby cat is crossed with a black cat?

Multiple Alleles Some traits have more than 2 forms of the gene. An example of this in humans is blood type. ABO blood groups Each individual is A, B, AB, or O phenotype A and B alleles are dominant to O. A and B alleles are codominant to each other.

Blood Types Blood Type: A B AB O Genotype AA or AO BB or BO AB OO

If a male is homozygous for blood type B If a male is homozygous for blood type B and a female is heterozygous for blood type A, what are the possible blood types of the offspring?

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

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

Rh Surface Protein In addition to the “A” and “B” proteins on the surface of red blood cells, there is another protein called “Rh”. It is called this because it was first discovered in the blood of the rhesus monkey. If a person’s red cells have the Rh protein, then they are typed “positive”. If a person’s red cells lack the Rh protein, then they are typed “negative”. Having the Rh protein is dominant to lacking it. The genotype for Rh+ is either RR or Rr. The genotype for Rh- is rr.

Identify the blood types

How is a person’s blood type determined? When an incompatible blood type enters a person’s body, the immune system produces antibodies to fight the blood cells. Antibodies bind to the A, B and/or Rh proteins on the surface and cause the blood to clump. This clumping is called agglutination. Blood types are determined by mixing a blood sample with antibodies to see if clumping occurs.

A-Anti B-Anti Rh-Anti Blood Type? Agglutination

Incompatible Heart Transplant Video

Gene Interactions Sometimes the expression of one gene can affect the expression of other genes in an organism. These interactions were not predicted by Mendel’s Laws. Examples of this are epistasis and pleiotropy.

Epistasis Epistasis is the interaction of two or more genes to control a single phenotype. Usually 1 gene controls the expression of another gene. Example: A labrador retriever’s coat color is controlled by two alleles: A dominant allele “B” will produce black pigment while the recessive allele “b” produces brown pigment. The dominant allele “E” turns on the “B” or “b” allele.

Labrador Retrievers BBEE, BBEe and BbEe --> Black retrievers bbEE and bbEe --> Brown retrievers BBee, Bbee, or bbee --> Golden retrievers

Epistasis Problem: What is the phenotypic ratio if you crossed two labradors that are heterozygous, BbEe, for these two genes?

Epistasis Problem - Solution

Pleiotropy ? Expression of a single gene which has multiple phenotypic effects Marfan Syndrome – mutated form of the gene for fibrillin. This gene can affect the heart (aorta), height, chest structure, flexibility of joints, length of fingers, etc.

Environmental Influence on Phenotype The environment can affect an organism’s phenotype. Examples: Soil acidity affects the color of hydrangea flowers. Temperature affects the color of the fur in Himalayan rabbits. Gender of clownfish is dependent on the “need” for males/females for reproduction. They are all born male but may become female if necessary.

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

Suppose a child is of blood type A and the mother is of type 0 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 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 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 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 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 Parents Blood Types Baby Blood type Mr. Hartzel O   Mrs. Hartzel A Jennifer Mr. Simon AB Rebecca Mrs. Simon Holly B Mr. Peach Mrs. Peach