Biology

A Punnett square is a diagram that predicts the possible genotypes of offspring from a genetic cross. It lays out the alleles from each parent along the rows and columns, and the boxes show every possible combination. From it you can estimate the expected ratios of traits in the offspring.

A dominant allele expresses its trait even when only one copy is present, while a recessive allele shows its trait only when two copies are present. Dominant alleles are usually written with a capital letter and recessive ones with lowercase. This is why an individual with one dominant and one recessive allele displays the dominant trait.

A codon is a sequence of three nucleotide bases that specifies a single amino acid during protein synthesis. With four possible bases, there are 64 codons in the genetic code, encoding 20 amino acids plus start and stop signals. For example, AUG codes for methionine and also serves as the start codon.

Hardy-Weinberg equilibrium describes a population whose allele and genotype frequencies stay constant across generations when no evolutionary forces act on it. It assumes no mutation, migration, selection, or genetic drift, and random mating in a large population. It serves as a baseline, so any deviation from it signals that evolution is occurring.