Question

3. Assume that in humans, right-handedness (R) is dominant over left-handedness (r). A left handed man marries a right-handed woman. They have ten children all right-handed. What are the genotypes of all individuals of this family? Dad = Mom = Kids =,

4. A right-handed man marries a left-handed woman. Their first child is left-handed. What are the chances that future children will be right-handed? _________% Left-handed?________%

5. Assume in humans that brown eyes (B) are dominant to blue (b) and right-handedness (R) is dominant over left-handedness (r). A brown-eyed, right-handed man marries a blue-eyed right handed woman and their first child is blue-eyed and left-handed. What are the genotypes of the two parents?

Mom _________

Dad __________

6. In humans, a type of blindness called aniridia (B) is dominant over the normal sighted individual (b). Migraine headache (M) is the result of a different dominant gene. A non-migraining man with aniridia whose mother was not blind marries a normal sighted woman who suffers from migraines but whose father did not. In what proportion of their children would you expect to have both aniridia and migraine to occur? __________

   7. A researcher believes, as a result of investigation, that the dark pigmented skin of the pure African is due to two pairs of factors, and that white skin is due to the absence of these factors. Let these factors be represented by AABB and the white skin by aabb. Since no skin is pure white (even in winter!). Assume that A = 30% of black, B = 20%, a = 2%, and b = 1%.

Now cross two individuals both with the genotype AaBb. List the percent of color and the number of individuals in each as the result of such a cross.

     

Answer 1

As given in question Right handedness R, is dominant over Left-handedness r. We humans are deploid and 2 sets of the chromosome. So each gene has the alternative form we called it as Allele, here Allele R is a dominant form for right-handedness over left-handedness r.

Man is left-handed i.e he mist have 2 copies of recessive allele r.

So genotype is rr.

Women are right-handed so she must have at least 1 copies of R. So genotype is Rr or RR. But here the genotype of women is RR because she has all children with right-handed, if she is heterozygous for Right handedness then 50% of children will left and right-handed just see by crossing

RR x rr

F1 Rr. The genotype of children.

all children are right-handed

2 Now in second case women are left-handed i.e rr and man is right-handed but here he must be heterozygous so both phenotypes will appear in progeny. So genotype is Rr.

Rr x rr

By Punnet square we get

	r	r
R	Rr	Rr
r	rr	rr

This result clearly gives us answer i.e 50% of children will right be handed and 50% of children will be left-handed.

3 (5) Here is two traits consider for the inheritance pattern

Eye colour and handedness (left or right)

Right-handed R is dominant over left-handed r and Brown eye B is dominant over blue eye b.

A brown eyes BB or Bb and Right-handed RR or Rr man marriage blue-eyed bb right-handed RR or Rr.

Now by children phenotype, we can easily predict the genotype of parents

The first children are blue-eyed bb and left-handed rr

So genotype is bbrr.

Now, this trait is not parental, so for this trait, parents should Heterozygous for the dominant trait. If the homozygous dominant genotype is there in parents, then above phenotype progeny will not be occurred.

So

Man genotype is

BbRr and women genotype is bbRr

BbRr x bbRr

Let's see punnet square.

In blue colour the genotype of first children shown while all other possibilities are also there

In red colour all children i.e 6/16 are brown-eyed and right-handed, in yellow colour, there are blue-eyed and right-handed children 6/16

In greenish colour, 2/16 children are brown-eyed and left-handed and 2/16 are blue-eyed and left-handed highlighted in blue colour.

Thanks