Question

One parent has a dominant gene for a

Answer 1

The probability of a child with a bent thumb  is out of 4 is 50%.

Explanation:

Information given:

dominant gene = straight thumb (genotype TT, Tt)

recessive trait = bent thumb (genotype  tt)

from the question genotype of parents can be deduced:

Parent 1 = Tt

parent 2 = tt

from the Punnet square:

  T     t

t  Tt    tt  

t   Tt    tt  

From the results of Punnet square it is seen that 50% of progeny will be straight thumb and 50% of progeny will be bent thump.

phenotype ratio and genotype ratio = 1:1

There will be 50 % probability that one of their offspring will be with bent thumb.

progeny with bend thump percent = $\frac{progeny with bent thumb}{total number of offspring}$ x100

                                        = 50%.