Non-Mendelian Genetics

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

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

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

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

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?

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

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? Phenotype Genotype O ii A IAIA IAi B IBIB IBi AB IAIB

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

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 ???

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

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: _____

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

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

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.

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!

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

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?