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

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.

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