Final answer:
A Punnett square shows the possible allele combinations from both parents during reproduction. It uses the laws of probability to predict genotypic and phenotypic ratios of offspring based on Mendelian genetics.
Step-by-step explanation:
A Punnett square shows the different combinations of the alleles of both parents that might occur during reproduction. This chart is particularly useful for visualizing the probabilities of genotypes that can arise from a particular genetic cross. When both parents are heterozygous for a certain gene, like flower colour with alleles 'P' for purple and 'p' for white, the Punnett square helps us predict the possible genotypes of their offspring. For example, with both parents having the genotype Pp, the Punnett square would show a genotype ratio for the offspring of 1 PP (homozygous dominant), 2 Pp (heterozygous), and 1 pp (homozygous recessive), assuming simple dominance.
Using a Punnett square to predict outcomes utilizes the laws of probability. It is based on Mendel's principles of segregation and the random fertilization event in which each combination of alleles is equally likely. The practice enables us to infer not only genotypic frequencies but also phenotypic ratios, given the inheritance patterns of dominance and recessiveness.