Pleiotropy, Epistasis, and Polygenic Inheritance

Question 1

What is pleiotropy and how does it relate to Mendelian gene expression? What are some examples of pleiotropy?

Answer 1

A case involving one gene controlling multiple characters; influence of one gene on multiple phenotypes
It defies the Mendelian concept of “one gene; one phenotype”
Ex –> White and deaf cats; PKU resulting in both mental disabilities and pale skin

Question 2

What is epistasis and how does it relate to Medelian gene expression? How is one gene able to mask or alter the phenotype of another gene?

Answer 2

Epistasis- a case involving one gene masking or altering the expression of another– the dominant allele blocks detection of the recessive allele(s)

Question 3

How does eye color genetics work in humans? Be able to identify the epistatic gene and the hypostatic gene in cases of epistasis?

Answer 3

Human eye color is determined by two different genes– bey2 determines whether brown pigment is produced, gey determines whether green or blue is produced
bey2 is epistatic to gey; gey is hypostatic to bey2

Question 4

What is meant by dominant and recessive epistasis?

Answer 4

Dominant epistasis- one trait is controlled by the presence of a dominant allele on another
Recessive epistasis- one trait is controlled by the presence of a recessive allele on another

Question 5

How does epistais often affect gene expression in metabolic pathways? What is the difference between duplicate recessive epistasis and duplicate dominant epistasis?

Answer 5

Epistasis often targets genes involved in the same metabolic pathways to result in varied conditions or results
Duplicate recessive- a dominant allele of both genes are required for an observed result
Duplicate dominant- homozygous recessive geneotypes for both genes are required for an observed result

Question 6

What is polygenetic inheritance? How can characters which are controlled by polygenic inheritance result in a continuous phenotypes (characters) and what role does the environment play in this process? Give examples

Answer 6

Polygenic inheritance- traits controlled by the additive effect of many genes
Because there are many variable involved, there can be nearly limitless traits for some polygenetic charaters
Ex –> Skin color

Question 7

What is multifactorial inheritance? How can the genetic continuation (heritability) of human diseases be determined?

Answer 7

Traits contolled by the additive effect of many genes plus the environment
Heritability can be studied by observation of twins in separate adopted families- study the effect of the environment

Question 8

Know the following ratios:
Recessive epistasis
Dominant epistasis
Duplicate recessive
Duplicate dominant

Answer 8

9 : 3 : 4
12 : 3 : 1
9 : 7
15 : 1