Question

1. How does the BEH2 allele in HERC2 affect eye color?

A - BEH2 prevents the green/gray gene from functioning so that eye color is dependent on the alleles present at the OCA2 gene

B - BEH2 prevents chromatin remodeling and the OCA2 promoter is unable to function

C - the BEH2 allele causes loss of function of the HERC2 gene, resulting in blue eyes

2. In the scitable article by Wray and Visscher, they discusss why heritability values can change over time. One way is if “genetic values” change; genetic values might change by which mechanism?

A - existing alleles contribute to phenotype only after a change in genetic background

B - new. Alleles can enter a population

C - all of these are circumstances that would change geneitc values

3. In the scitable article on epistasis by Lobo, she discusses the Alzheimer’s susceptibility allele apoliopoproteinE4 (apoE4) However, having the allele does now always lead to Alzheimer’s. How does she explain this phenomenon?

A -environmental risk factors must also be present for Alzheimer’s to occur

B- - epistatic interactions apoE4 and other genes such as beta-secretase influence the risk of Alzheimer’s

C - 27 genes are required for Alzheimer’s and all 27 must be present for the liability threshold to be crossed and for disease to occur, not just apoE4

4. If monozygotic twins reared apart show concordance for osteoarthritis at about 35% and dizygotic twins reared apart show concordance for osteoarthritis at about 15%, a reasonable estimate of heritability might be

A - 20

B - 40

C - heritability describes variance, and cannot be estimated from concordance

5. A widely presented model for eye color claims that there are two genes, we can call them B and G, which generate eye color, through an additive model. Which statement is true of this model

A - this is widely considered to be accurate, and explains all eye colors

B - the model is considered to be inadequate in that we now know that three genes seem to be required to explain the full range of eye colors

C - this model is too simplified and fails to explain

Answer 1

1. The OCA2 gene and HERC2 gene are located very close to each other and both influence the eye color. Eye color shows polygenic inheritance since the eye color is dependent on a number of different genes which all have direct or indirect influence on each other's expression. The OCA2 gene is primarily responsible for the production of melanosomes and subsequently melanin pigment, so it leads to brown color of iris. However, HERC2 gene can influence expression of OCA2 significantly. Less is the melanin, light will be the color of iris. BEH2 (blue eyes haplotype) allele present on the HERC2 gene can cause the OCA2 gene functioning to'switch off', thereby melanin pigment by protein is not formed and this results in blue color eyes, especially prevalent in Europeans. Option B is correct.

2. Genetic variance can be defined as the changes in the genetic configuration of a species that might or might not result in changes in phenotype. The change in genetic values can either be due to migration to or from other geographical location, mating with a different genotype individual or simply because of a mutation in a gene that is expressed over generations in a particular phenotype. Therefore, genetic values are influenced by a number of factors. option C is correct.

3. Alzheimer’s disease is a progressive neurodegenerative disorder. Apolipoprotein E4(apoE4) is the allele present that renders an individual susceptible to the development of Alzheimer's disease. However, on research, it was found that simply the presence of apoE4 wasn't sufficient for the disease to develop. In fact, epistatic interaction around 27 genes is responsible for the expression of this disease. These interactions can be synergistic ( increasing the risk) or antagonistic( reducing the risk). Some major interaction includes apoE4 with beta-secretase influences the risk of Alzheimer's. Option B is correct.

4. Concordance can be defined as the probability of a trait being expressed equally in both individuals of a pair of twins(monozygotic or dizygotic). However, the heritability of a trait is not simply determined, it is a product of a number of environmental and genetic factors that surround an individual. Heritability can't be described as constant but variable,subject to the different conditions. Option C is correct.

5. Eye color in humans is a polygenic inheritance, resultant of the interaction of 8 different genes. various genes interact to give different eye color, the expression of each gene controlled by the others. It doesn't work on a simple additive model as incomplete dominance also plays a major role in determining eye color. Option C is correct.