Non- Mendelian Genetics

1. Non-Mendelian Genetics

2. Non-Mendelian Genetics • Non-Mendelian Genetics do not follow Mendel’s Laws: • Principle of Dominance – the dominant allele is masks the recessive allele • Two types of Non-Mendelian Genetics • Incomplete dominance • Codominance • Other special genetic cases • Multiple Alleles • Sex-linked traits

3. Incomplete Dominance • In some cases, one allele will not be completely dominant over the other allele. • Results in a blending of the two alleles • A red snapdragon is crossed with a white snapdragon and the resulting offspring will all be pink

4. Incomplete Dominance Example • Andulsian fowls exhibit incomplete dominance. Black individuals (B) and White individuals (W) are both homozygous and heterozygous individuals (BW) are a bluish gray. Draw a Punnett square and give the genotypic and phenotypic ratios of a cross between bluish gray birds

5. Codominance • In some cases, both alleles are dominant and expressed at the same time • Generally results in a spotted appearance • In chickens, black chickens crossed with white chickens result in erminette chickens which have black and white feathers

6. Codominance Example • The Asian flower Camellia exhibits codominance in the form of white spots. If a white flower is crossed with a pink and white flower, what are the genotypic and phenotypic ratios of the offspring?

7. Multiple Alleles • In some cases, more than just 2 alleles exist in the population. • The gene is said to have multiple alleles • The multiple alleles can follow any of the inheritance patterns that we have talked about • Example – Blood Types • IA • IB • i (type O blood in homozygous state) • IA and IB are codominant to each other and dominant to i

8. Multiple Allele Example • Cross a man with type AB Blood with a woman that has type O blood. What kinds of blood types could their children have?

9. Sex Linked Traits • The sex chromosomes are referred to as X or Y • Males are XY • Females are XX • Somes genes are only present on one of the sex chromsomes (usually the X) • XAXa - female with recessive allele, but dominant phenotype • XaY - male with recessive allele and recessive phenotype • Examples – color blindness, male pattern baldness

10. Sex Linked Trait Example • Hemophilia is a rare hereditary human disease of the blood in which the blood does not clot properly. A normal man marries a normal woman and they have a son with hemophilia. Can they have a daughter with hemophilia? Show your work using a Punnett square. • Dad XHY • Mom _______ • Son XhY • Daughter ???

11. Polygenic traits • Traits that are the results of two or more genes. • Examples: human skin color, eye color, and height

12. Polygenic practice problem • Skin color in humans is determined by a polygenic inheritance system, possibly involving involving as many as 9 genes. For simplicity let’s consider the influence of 3 genes: A, B, and C, where the dominant allele darkens skin color. Suppose a women who is AABbCc mates with a man who is AaBbcc. • A. List all of the possible genotypes of the gametes that could be produced by each the parents? • : ______________ : _______________ • B. Draw a Punnett square that shows the genotypes possible, and number each genotype from lightest (1) to darkest skin coloration. • C. In this cross, how many dominant alleles will children with the darkest skin coloration possess, and what theoretical fraction of the children will have this coloration? • # of alleles: ____ fraction: _____

13. Epistasis • The ability of one gene to overshadow or overpower the expression of other genes. • Examples: albinism, fur color in Labrador retrievers

14. Labrador Retrievers • Fur color in Labrador Retrievers is controlled by two separate genes. • Fur color is a polygenic trait! Gene 1: Represented by B : Controls color Gene 2: Represented by E : Controls expression of B

15. Labrador Retrievers • If a Labrador retriever has a dominant B allele, they will have black fur. • If they have two recessive alleles (bb) they will have brown fur.

16. Labrador Retrievers • If a retriever receives at least one dominant “E” allele, they will remain the color that the “B” allele coded for. • Either black of brown • However, if a dog receives a pair of homozygous recessive “e” alleles, they will be golden regardless of their “B” alleles!

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

18. Try this cross… • You have decided to cross your golden retriever (bbee) with the neighbor’s chocolate retriever (bbEe). What color pups will they have?