Which diagram shows all possible allele combinations in a genetic cross?

• A. Karyotype
• B. Genetic linkage map
• C. Trait chart
• D. Punnett Square

Answer: (D)

When predicting the outcomes of a genetic cross, you need a diagram that lists every possible combination of what each parent can contribute. A Punnett square does this by placing the possible gametes from one parent along one axis and the gametes from the other parent along the other axis, then filling in each cell with the resulting genotype. This layout shows all allele combinations that could appear in the offspring and makes it easy to read the probabilities for each genotype (and thus phenotype, if you know the trait).

For example, crossing two heterozygotes for a single gene with alleles A and a yields four possible offspring genotypes: AA, Aa, Aa, and aa, all visible in the grid. Other diagram types aren’t designed to enumerate these combinations: a karyotype shows chromosome number and structure, a genetic linkage map shows gene positions on a chromosome, and a trait chart tracks observed traits rather than all possible allele pairings in a cross. So the square that pairs parental gametes to reveal every potential allele combination is the Punnett square.