A Punnett Square.
Invented by Professor Reginald Crundall Punnett FRS (20 June 1875 - 3 January 1967)
A table used to predict the phenotype of the offspring of two known parent organisms. The punnett square can also be used to carry out a back cross. This is a technique where the phenotype of the offspring is used to determine the genotype of one or both of the parental organisms.
A punnett square can be used in order to assess the probability of offspring inheriting a particular trait from its parents. In general, a capital letter (e.g. A) indicates a dominant allele, whilst a lower case letter (e.g. a) indicates a recessive allele. The assumption is made that the likelihood of inheritance of each allele from each parent will be 0.5. For example, for a parent of genotype Aa, P(A)=0.5 and P(a)=0.5. If a parent is homozygous (AA or aa), the probability of inheriting the allele will be 1.