Punnett Square
n.
Definition: A tool that helps show all possible allelic combinations
Table of Contents
Punnett Square Definition
A tool that helps to show all possible allelic combinations of gametes in a cross of parents with known genotypes in order to predict the probability of their offspring possessing certain sets of alleles.
More Info on Punnett Square
Punnett Square makes use of a grid and letters. In particular, capital letters represent dominant alleles and lower case letters to recessive alleles. With this tool, the known genotypes of each parent are shown to help predict the possible genotypes of their offspring. It shows how alleles are inherited or passed on to offspring from parents.
It is typically applied in monohybrid crosses and dihybrid crosses in which the theoretical outcomes are based on the assumptions of segregation and independent assortment of alleles (according to Mendelian inheritance).
Deviations from the expected outcomes are observed in the following conditions:
- a cross involving linked genes or alleles on the same chromosome
- a cross in which one parent lacks a copy of a gene, e.g. males with only one X chromosome
- a cross wherein it results in an offspring with a genotype not compatible with life
- a cross involving alleles showing incomplete dominance or codominance
- a cross involving genetic interactions (epistasis) between alleles of different genes
- a cross involving alleles that are imprinted
- a cross involving the maternal effect
Word origin: named after Reginald Punnett, British geneticist, who developed it.
Also called: checkerboard.
