Question

 

1. If the percent recombination between A and B is 12, Between A and C 4, and between B and C is 8 then the order of the genes on the chromosome is?

 

2. A man who is homozygous for type A blood has a child with a woman who is homozygous for type B blood. What is the probability that this child will have type AB blood?

 

3. In familial hypercholesterolemia, individuals homozygous for the allele causing the disorder completely lack receptors on liver cells that take up cholesterol from the bloodstream. Heterozygotes have one-half the number of receptors while individuals homozygous for the normal allele are phenotypically normal. This is an example of _____.

 

 

Answer 1

1. Yes, you are correct.

2. It is clearly mentioned that both parents are homozygous.

Man - homozygous to blood type A - IA IA

​​​​​​Woman - homozygous to blood type B - IB IB

So, if they are crossed, the child will be AB. No other options left here. If any one of them were heterozygous, there is a chance for any other blood type may found. But here, as they are homozygous, the chance for AB blood type is 100%.

I hope you understood the concept well.

3. It is incomplete dominance.

First of all, you should be thorough with the concept of complete dominance. It is a form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive.

Here in this case,

Take alleles for familiar hypercholesterolemia as F (dominant) and f (recessive).

Homozygous dominant - FF - lack of receptors

Heterozygous condition - Ff - half number of receptors

Homozygous recessive - ff - normal

So if it is complete dominance, there will be lack of receptors in heterozygous condition (if dominant allele, F dominate the recessive allele, f). So the answer is not complete dominance.

It is incomplete dominance in this case. It is a form of dominance in which one allele for a specific trait is not completely expressed over its paired allele, right. This results in a third phenotype in which the expressed trait is a combination of the phenotypes of both alleles.

For example in roses, pink colour occurs when red roses mated with white ones. This caused the color of the roses to become a bit different i.e., in between.