Two people (BOTH heterozygotes) are able to taste a chemical substance called PTC. The ability to taste PTC is

Question

Two people (BOTH heterozygotes) are able to taste a chemical substance called PTC. The ability to taste PTC is caused by a dominant allele (T). The inability to taste PTC is caused by a recessive allele (t).

Refer to Exhibit 4-1. What proportion of their children would be expected to have the ability to taste PTC?

a. 3/4

b. 1/2

c. All

d. 1/4

e. 2/3

Answer 1

a. 3/4

Counting the expansion (T + t)(T + t) = TT + 2 Tt + tt

1 genotype-TT offspring : can taste PTC

2 genotype-Tt offspring : can taste PTC because T is dominant over t

1 genotype-tt offspring : cannot taste PTC

There are a total of 3 phenotypes out of 4 possible combinations who can taste PTC.

Answer 2

3/4 of the children will bw able to taste ptc.

ptc+/ptc+   homo for tasting ptc

ptc-/ptc+   hetero for tasting ptc

ptc+/ptc-   hetero for tasting ptc

ptc-/ptc-... homo ptc insenstive. Only this one won't taste the ptc

Answer 3

a. 3/4

there children will be TT, Tt, tt in the ratio 1:2:1 the offspring able to taste the PTC are those having T whether homo or heterozygous so they are 3/4 of the offsprings.

Answer 4

i would say a.

T: able to taste PTC

t: Inable to taste PTC

As they are hetrozygous they would both be Tt.  

So for the first person 1/2 of their alleles would be T and the other half would be t. This is the same for the second person.

So know you 'cross' them by timesing as shown below...

(1/2T + 1/2t)( 1/2T + 1/2t)

This is gives:

1/4TT     &    2/4Tt     &      1/4 tt

As the ability to taste PTC is dominant any with a T will have the ability to taste PTC

so add the    TT & Tt results together and you get 3/4 which is A.

You can also do a punnet square which would give the same results.