Question

How do I make and use a Punnett square?

Answer 1

Punnett Square is used to get the genotype and phenotype ratio of offspring by crossing the gene of the parents. The number of squares in Punnett squares is dependent upon the number of parental composition and their gene combinations.

Complete answer:
Punnett square was discovered by Reginald. C Punnett, which is a square shape diagram used to predict the genotype and phenotype of offspring from a breeding experiment by crossing the gene of parents. The number of Punnett squares in the diagram is based on the number of traits used. After drawing the boxes the gene of one parent is placed at top and the gene of another parent is placed on the left side of the box. Only one letter with a single trait goes over one box in case of monohybrid cross whereas two letters with two different traits go over one box. By crossing the trait the number of the possible genotypes of offspring obtain. For example in the case of flower colour let the dominant gene is Y for yellow colour flower and gene y for orange colour flower. Each parent carries two genes, so to carry out the result of breeding between dominant and recessive Punnett square diagrams are used by placing a YY gene on top and a yy gene on the left side of the box.

| Y| Y
---|---|---
y| Yy| Yy
y| Yy| Yy

So the genotype obtained in offspring is all heterozygous.

Note:
Pedigree chart and Punnett square both used to carry out the gene of offspring by crossing the parental gene but Pedigree chart used to analyse the generation graphically like a family tree or it also helps to check the transmission of disease from generation whereas Punnett square has no role on how disease transmitted from generation to generation.