If both parents are heterozygous for a trait, the probability that an offspring will be recessive for that trait is

If both parents are heterozygous for a trait, the probability that an offspring will be recessive for that trait is 1/4 or 25%. Heterozygous means that an individual has two different alleles (versions of a gene) for a particular trait. One allele is dominant, and the other allele is recessive. The dominant allele is expressed in the phenotype, or physical appearance, of the individual, while the recessive allele is only expressed in the phenotype if the individual has two copies of the recessive allele. When two heterozygous parents (Aa x Aa) have offspring, each parent can pass on either the dominant allele (A) or the recessive allele (a) to their offspring. The possible combinations of alleles that can be passed on from each parent are: AA, Aa, aA, and aa. Only the aa genotype results in the recessive trait being expressed in the offspring's phenotype. The probability of an offspring inheriting an a allele from one parent is 1/2, and the probability of inheriting an a allele from the other parent is also 1/2. Therefore, the probability of an offspring inheriting two a alleles (aa genotype) is the product of these probabilities, which is 1/2 x 1/2 = 1/4 or 25%.