Question

Trekian Fur is a dominant trait. Trekkies (on the planet Gomaz) from a pure-breeding population with the Trekian Fur gene are scored for their phenotypes. The two alleles at the Trekian Fur gene are T (dominant) and t (recessive).


80% of the Trekkies from this colony (genotype TT) have Trekian Fur; 20% of the Trekkies look wild-type.


Also, the penetrance of the Trekian Fur phenotype is 65% in the heterozygous Trekkies.


Pure breeding wild-type Trekkies (tt) show the Trekian Fur phenotype 10% of the time. Thus, the penetrance of Trekian Fur is 10% in homozygous wild-type Trekkies.


Problem: If two heterozygotes for the Trekian Fur gene (Tt x Tt) are crossed, what proportion of the offspring are expected to show the Trekian Fur phenotype?


A. 80%.

B. 55%.

C. 45%.

D. 50%.

E. 20%.

Answer 1

Answer:

B. 55%.

Explanation:

TT = 80percent progeny that exhibit Trekian fur phenotype

Tt = 65% progeny exhibit Trekian fur phenotype

tt = 10% progrny exhibit Trekian fur phenotye

parent cross ; TT x Tt

progeny ; TT Tt tt

TT = 25% ; percentage of progeny that exhibit Trekian fur phenotype = 25 x 0.8 = 20%

Tt = 50% ; percentage of progeny that exhibit Trekian fur phenotype = 50 x 0.65 = 32.5%

tt = 25% ; percentage of progeny that exhibit Trekian fur phenotype = 25 x 0.1 = 2.5%

Total = 20 + 32.5+ 2.5 = 55%