Question

Using your own words, describe how a person builds a Punnett square to determine genotypic and phenotypic ratios in the offspring of the hypothetical mating of two monohybrid parents. Pick any trait that is controlled by a single set of alleles and simple dominant-recessive inheritance.

Answer 1

To calculate phneotypic and genotypic ratios, two types of methods are used
1. Fork line method
2. The Punnett square method

The Punnett square method is an easy, efficient, and rapid method. In this method, gametes produced by one parent are written at one side of the table (left side) and the gametes produced by the other parent are written on the top of the table. Each combination is written in each box of the table.

T = Dominant allele = Tall
t = Recessive allele = Dwarf

Parental cross: TT X tt
F1 progeny: Tt
F1 selfing: Tt X Tt
F2 progeny: TT Tt Tt tt
Phenotypic ratio = 3:1
Genotypic ratio = 1:2:1

See the image for the Punnette square