1. Going Beyond Mendel. Chapter 11

2. However, sometimes a genetic trait can be controlled by:
Introduction
Sometimes one gene simply controls a one trait (another reason why Mendel was lucky—genotypes matched phenotypes)
However, sometimes a genetic trait can be controlled by:
a number of genes that interact with each other with some being dominant over other and…
the “conditions” the gene is under to finally produce the phenotype.

3. Dominance Relationships and Gene Interactions
There are various ways in which two alleles of a gene can affect the phenotype.
Often they are simply dominant or recessive
Other times, there are situations where the recessive allele may function a little or interact with the dominant allele.

4. 1. Incomplete dominance (partial dominance)
phenotype of a heterozygote is between the two phenotypes of the two homozygotes
Example
cR cR = red flowers
cW cW = white flowers
cR cW = pink flowers

6. the equal expression of both alleles resulting in a mixed phenotype.
2. Codominance
the equal expression of both alleles resulting in a mixed phenotype.
examples
Cattle –
Blood type/group –

8. 3. Multiple alleles
Himalayan Rabbit example

9. Blood type/group example

11. alleles that cause the death of the organism recessive lethal alleles
4. Lethals
alleles that cause the death of the organism
recessive lethal alleles
Corn:
Huntington’s disease

12. 5. Epistasis
one gene interferes with the expression of another gene. Fig 11.8 in text
Example
B = black mouse
b = brown mouse
C = makes the pigment melanin necessary for either black or brown
c = can’t make pigment necessary for either color

14. Conditional Phenotypes
How genes are expressed depends on the conditions under which they exist
The same genotype can result in different phenotypes in:
separate individuals
different tissue of the same individual

15. Environment

16. Development
As an organism grows from fertilized egg to a mature organism, certain nerves and tissues may or may not be “completed”
incomplete penetrance -
variable expressivity –
Ex.) Polydactyly: tendency to have extra fingers or toes

18. a sex-limited or linked trait shows up in only one sex or the other
Ex.) uteran cancer.
a sex-influenced trait can affect both sexes but the effect is different.
Ex.) middle-aged male go bald but women’s hair only thins.

19. Some genetic traits can have variable ages of onset
Ex.) muscular dystrophy, Huntington’s disease, and baldness.

20. Pleiotropy Example Phenylketonuria (PKU)
Victims can’t metabolize a.a. phenylalanine which then builds up and leads to brain damage.
Victims also have light hair and skin color.

21. Polygenetic inheritance
Examples
skin color:
height:
intelligence
birth weight