Concept:Gametes carry alleles, so the genotypes of offspring can be traced backward to identify the alleles present in each parental gamete.
Explanation:Each offspring receives one allele from each parent.
Study the offspring genotypes shown in the cross and work backward to determine which allele each gamete must have supplied.
Comparing the alleles found in the offspring with the parental contribution shows the pattern clearly.
Gamete I supplies
T.
Gametes II, III and IV each supply
t.
This gives the gametic combination
T,
t,
t, and
t.
Answer:Gametes I, II, III and IV respectively are
T,
t,
t, and
t.
Correct option: B.
