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

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?