How many gametes will be formed in the pea plant having genotype RrTT?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Two
By Mendel’s law of segregation, each gamete gets one allele of each gene. By the law of independent assortment, the alleles of different genes combine freely.
Gene R: the plant is Rr, so a gamete gets R or r — 2 kinds.
Gene T: the plant is TT, so every gamete gets T — 1 kind.
Gametes: RT and rT — 2 × 1 = 2 kinds.
A quick rule: the number of kinds of gametes is 2n, where n is the number of heterozygous genes. Here n = 1, so 21 = 2.
Option (1) One — Incorrect. One kind of gamete comes only from a plant homozygous for both genes, such as RRTT.
Option (3) Four — Incorrect. Four kinds come from a plant heterozygous for both genes, RrTt.
NCERT Extract:
Law of Segregation – “… Though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors. Of course, a homozygous parent produces all gametes that are similar while a heterozygous one produces two kinds of gametes each having one allele with equal proportion.”