Final answer:
A Punnett square is a diagram used in genetics to predict the offspring's genotypes and phenotypes from a cross between two parents. It operates based on the laws of probability and determines the ratios of genetic combinations.
Step-by-step explanation:
A Punnett square is a chart used in genetics to predict the genetic variations in the offspring resulting from a cross between two parents. It visualizes the transmission of hereditary traits and can be utilized to determine the expected percentages of different genotypes and phenotypes.
To construct a Punnett square, the possible gametes of each parent are listed on the top and side of the grid, respectively. Each box within the grid represents a possible genotype of the offspring, with alleles from both parents combining.
For instance, in pea plants, if the dominant allele for a trait is 'Y' for yellow seeds and the recessive allele is 'y' for green seeds, and both parents are heterozygous (Yy), the Punnett square will show the proportions of offspring that could have yellow or green seeds.
The resulting genotypic ratio would be 1:2:1 for YY:Yy:yy, with a phenotypic ratio of 3:1 for yellow to green seeds, assuming complete dominance of yellow over green.