1. Into the Genetic Frontier
Beyond Mendel
Into the Genetic Frontier

2. Mendel is the tip of the “genetics iceberg”
Mendelian Genetics
Mendelian Genetics The Rest of Genetics
As people have studied genetics, they have realized that the inheritance of traits is much more complex than Mendel’s work with peas indicated.

3. Polygenic traits Some traits which have many possible
phenotypes are controlled by more than one gene.
- the interactions of these genes allows for the large numbers of phenotypes.
- human examples: Hair, eye and skin color

4. The Inheritance of Eye Color
Only partially understood.
at least 3 different genes with 2 alleles each are responsible for eye color.
– bey 1 bey 2 and gey
These genes code for the formation of the pigment melanin
The function of only 2 of the 3 genes is currently understood

5. The Inheritance of Eye Color as it is Currently Understood
Known as the 2 gene model
One gene known as bey 2 has 2 alleles B for brown eyes and b for blue eyes
The other gene known as gey has 2 alleles G codes for green eyes and g for blue eyes
Evolution of eye color- not understood. One theory melanin was useful in tropical climates, but as people moved north, less sun required less melanin. One other idea, the color blue allows more light to pass through the iris reducing depression in the winter due to SADS

6. The 2 Gene Model - B is dominant to all other alleles-
BBGG,BBGg,BBgg,BbGG
BbGg,Bbgg = Brown eyes
- G is dominant to b
bbGG , bbGg = Green eyes
- bbgg only = blue eyes
How to figure out eye genetics – dihybrid cross

7. Pleiotropy-one gene multiple traits
When a single gene influences multiple traits this is known as Pleiotropy
example: Marfan’s Syndrome
- a dominant disorder caused by a single gene
- the defective gene causes individuals to be tall and skinny with very long fingers,
hyper joint mobility, eye and heart defects

8. More Pleiotropy-Marfans
Marfans is the result of a mutation that affects an enzyme that converts phenylalanine into tyrosine
Pleiotropy is thought to occur when a gene codes for a protein that is involved in a several processes

9. Epistasis
The action of one gene influencing the expression of another.
-Example:
In mice the color is controlled by one gene with 2 alleles
- the allele for gray (G) is dominant to the allele for black (g)
- Another gene controls an early stage in the development of hair pigment
- normal color development (A) is dominant to no color development(a)
- AA, Aa = color production
- aa = no color production = albino mouse

10. Epistasis in mice
The gene for color production influences the expression of the gene for fur color

11. More Epistasis – Bombay Phenotype
influences the expression of A and B blood types
- the gene involved is responsible for the formation of antigens on blood cells.
The dominant form of the gene allows the formation of antigens
HH or Hh allow antigens to form
The recessive form prevents the formation of antigens
hh means no antigens form

12. -If an individual is HH or Hh for blood antigen formation then: AA, AO = A blood BB, BO = B blood AB = AB blood -If an individual is hh for blood antigen formation then: AA, AO = O blood BB, BO = O blood AB = O blood

13. Environment Can Influence Gene Expression
example: Siamese cats
- Siamese coloring is a partial
albinism. Most of the cat is white
-Black fur is only expressed in areas
where the temperature is lower than
the rest of the body
- if black hair is shaved and the area kept warm then the hair that grows back will be white
- if white hair is shaved and the area is cooled,
then the hair will grow back black
The Siamese color is recessive and only shows up in homo recessive cats. The same gene for fur color also controls crossed eyes associated with siamese. Albinism is associated with crossed eyes in many species Pleiotropy