Question

In a typical monohybrid cross, F2​ population ratio is written as 3: 1 for phenotype but expressed as 1: 2: 1 for genotype. Explain with the help of an example.

Answer 1

Hint:Monohybrid cross is a cross between two plants, which differs in only one pair of contrasting characters . In monohybrid cross the two plants differ only one pair of contrasting characters for example the cross between tall and dwarf pea plant.

Complete Answer:
This is an example of monohybrid cross . following Steps are involved in the cross
>Selection of two pea plants with contrasting characters, tall and dwarf pea plant.
>Removal of anthers of one plant to avoid self pollination.
>Collect pollen grains from the other plants which are then transferred to the female parent for pollination.
>Collection of seeds and producing offsprings
>When a tall pea plant with the T dominant allele having genotype TT is crossed with a dwarf pea plant having t recessive allele with genotype tt, then the F1 generation will have all tall plants with genotype Tt ,
$TT \times tt $
F1 generation
Genotype Tt (all tall plants) and a cross between two F1 generation hybrids will result in one homozygous tall plant (TT), two heterozygous tall plants (Tt) and one dwarf plant (tt). So, the genotypic ratio will be 1:2:1. However, since three of the plants are tall and one dwarf, the phenotypic ratio can be said to be 3:1. It can be represented by the picture shown below.
From the test it can be found that alleles of parental pairs segregate from each other and only one allele is transmitted to the gamete. Gamete TT will have only T alleles. Gamete tt will have only t allele but gametes of Tt will have both the T and t gamete.

Note: Genetics is the branch of biology that deals with inheritance and variation of characters from parents to off springs. Characters are passed on from the parents to offspring by the process of inheritance.