Biology as Poetry: Genetics

Bacteriophage Ecology Group

Punnett Square

Means of visually probability theory calculations particularly for estimating genotype frequencies among progeny of specific crosses.

The Punnett square is most useful for crosses in which only a single locus is considered since these involve only a 2 × 2 output. To some degree the Punnett square may also be employed where two loci along two alleles at each locus are considered. The resulting 4 × 4 matrix is about as large as may be useful, however.

By three loci, with two alleles at each, the size is already up to 8 × 8, or 64 total combinations. Consequently, for doing genetics calculations above the very basic it is imperative that one learn the basics of probability theory.

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