Question

Tall plant with round seeds (TTRR) is crossed with a dwarf plant having wrinkled seeds (ttrr) . ${ F }_{ 1 }$ plants are tall with rounded seeds. Types of gametes produced by them would be,
(a) One
(b) Two
(c) Three
(d) Four

Answer 1

Hint: This cross is based on Mendel's Law of Independent Assortment which states that the inheritance of one trait does not affect the inheritance of another. According to his experiment, the number of gametes produced in the ${ F }_{ 1 }$ generation will be more than three.

Correct step by step answer:
The Dihybrid cross is a cross between two different genes that differ in two observed traits or a breeding experiment between two organisms which are identical hybrids for two traits.
When a dihybrid forms a gamete, each gamete receives only one allele for each character. Thus, the assortment of an allele of different characters during gamete formation is independent of their parental combinations which means the characters are inherited independently by the offspring even if they are present together on a single chromosome.

During an experiment when a pure tall plant with round seeds (TTRR) is crossed with a dwarf plant having wrinkled seeds (ttrr) . The gametes formed are TR and tr. In the first ${ F }_{ 1 }$ generation, all the plants are tall with rounded seeds that mean the ${ F }_{ 1 }$ progeny TtRr is formed. When it is considered in terms of self- pollination and self- fertilization, four types of gametes are formed. They are TR, Tr, tR, and tr. The TR represents tall and rounded seeds, Tr represents tall and wrinkled seeds, tR represents dwarf and rounded seeds, and tr represents dwarf and wrinkled seeds.
So, the correct answer is, ‘four’.

Note:
- The purpose of a dihybrid cross is to determine if any relationship existed between different allelic pairs.
- The 9:3:3:1 is the classic Mendelian phenotypic ratio for a dihybrid cross in which the alleles of two different genes assort independently into gametes.
- In a monohybrid cross the inheritance of one single trait is studied. The cross between homozygous dominant and homozygous recessive genes for a single trait is also called a reciprocal cross.