Carrying out a genetic cross

• Genetic crosses of single gene combinations (monohybrid inheritance) can be shown and examined using Punnett squares
• Punnett squares show the possible offspring combinations that could be produced and the probability of these combinations can be calculated
• In a genetic cross involving pea plants with alleles for height (T for tall and t for short), all possible offspring will have the allele combination Tt, resulting in tall plants
• During fertilisation, allele combinations created are a random process, and probability is used to determine the likelihood of each offspring combination
• You can express the outcome of a genetic cross using probability, direct proportion, or ratios
• Examples of genetic crosses can involve different allele combinations such as Dd and dd, resulting in offspring with different allele combinations
• Most phenotypes are controlled by multiple genes, not just a single gene
• The extent to which something is likely to be the case is known as probability
• It is important to always write the dominant allele first when constructing Punnett squares