Question

Multiple choice:

1) Which of the following can effect the expression of a phenotype?

A. environment

B. epistasis

C. incomplete penetrance        

D. variable expressivity

E. all of the above

2) Humans with the disorder PKU develop light colored hair. What kind of genetic effect is this?

A. epistatic

B. pleiotropic                  

C. phenotypic                 

D. variable expressivity                                                                                             

E. incomplete penetrance

3)The ability to produce the M and N antigens is determined by a gene with two alleles. Heterozygotes for the trait produce both kinds of antigens. What is this an example of?

A. incomplete dominance

B. partial dominance                  

C. codominance                                                                             

D. semidominance                        

E. A and B

4) A man has inherited an allele that codes for blue hair, but his hair is brown. This is a possible example of:

A. variable expressivity.

B. incomplete penetrance.       

C. an environmental interaction.

D. an epistatic interaction.

E. all of the above

Answer 1

1) E- all of the above

Temperature, drugs, light exposure etc. can influence genetic expression and thus the phenotypic expression.

Epistasis describes how gene interactions influence phenotypes.

Reduced/incomplete penetrance means those with mutated gene may not express the symptoms for the disorder and variable expressivity refers to a variation in development of symptoms amongst those who have the gene. thus, we conclude all are responsible in effecting expression of a phenotype.

2) B - pleiotropic

In pleiotropy a single gene has the capability to influence phenotypic traits that me seem unrelated. PKU causes an increase of phenylalanine in the body due to defect in just one gene, eventually leading to problems in multiple systems, albinism and light hair color.

3) C- codominance

This is because either one or even both antigens may be expressed in the MN blood group system. Codominance is where both allele contributions are visible in the phenotype. One allele does not override the effect of the other.

4) C- incomplete penetrance

This may be the best answer for this question for the reason that most humans will never have blue hair naturally so assuming this man may have inherited a mutation for blue hair. This means most people who possess the mutation will not develop the phenotype. The reason for incomplete penetrance may furthur be linked to genetic interactions and environmental factors but the primary reason is incomplete penetrance.