Question

Suppose that, in humans, ability to roll the tongue (R) is dominant to being unable to roll (r), and having freckles (F) is dominant to having no freckles (f). If a woman heterozygous for both traits married a man with no freckles who couldn't roll his tongue, what is the probability that they would have a freckled, tongue-rolling child?

A. 3/16
B. 9/16
C. 1/4
D. 3/4
E. 1/16

Answer 1

Answer:

C. 1/4

Explanation:

From the question, we can deduce that

R = abililty to roll tongue

r = inability to roll tongue

F = having Freckles

f = no Freckles

So, if a woman heterozygous for both traits , (i.e RrFf ) married a man with no freckles who couldn't roll tongue (i.e rrff )

The question ask us what is the probability that they would have a freckled, and tongue-rolling child. (i.e RrFf )

The probability is 1/4

The self cross of each parents goes thus,

RrFf = RF, Rf, rF, rf

rrff =  rf, rf, rf, rf

Lets look at the dihybrid cross between both parents in order to determine the probability of the child that will have  a freckled, and tongue-rolling traits.

RF, Rf, rF, rf ×   rf, rf, rf, rf

= RrFf, Rrff, rrFf, rrff

= RrFf, Rrff, rrFf, rrff

= RrFf, Rrff, rrFf, rrff

= RrFf, Rrff, rrff, rrff

RrFf (i.e freckled, tongue-rolling child) = 4/16

=1/4

i also attahed a file, that clearly depicts the cross using a punnet square.