One parent has a dominant gene for a
straight thumb and a recessive gene for a
bent thumb. The other parent has two
recessive genes for a bent thumb. Let T
represent straight thumbs and t represent
bent thumbs. What is the probability, or
possibility, that one of their children will
have a bent thumb?
The probability of a child with a bent thumb
is out of 4, or
%.

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 = x100

                                        = 50%.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."