Question

In a cross of a round hybrid pea with a true breeding round parent (Rr x RR), what genotypic proportions would be observed in the offspring?

• A. Half heterozygous, half homozygous dominant
• B. Half round, half wrinkled
• C. All are homozygous
• D. All are heterozygous

Answer 1

Answer: (A)

Law of segregation states that the two factors for a trait, present together in a heterozygous individual (Rr), do not get mixed and are separated and delivered singly during gametogenesis. Thus, heterozygous variety will produce two types of gametes: 50% gametes with “R” and 50% with “r”. The homozygous dominant variety will make all gametes with “R” allele only. Random fertilization of gametes of two parent plants will obtain RR (homozygous dominant) and Rr (heterozygous dominant) genotypes in 1:1 ratio. A homozygous individual carries two copies of the same allele while heterozygous has two contrasting alleles for a gene/trait. Both RR and Rr genotypes exhibit dominant phenotype (round seed shape) because expression of the recessive allele in heterozygous variety is masked by the presence of dominant allele. Thus, the correct answer is option A.