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Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state. Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote. Locus: the particular position on homologous chromosomes of a gene.Homozygous: having two identical alleles of a gene. Heterozygous: having two different alleles of a gene. Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.ocus: the particular position on homologous chromosomes of a gene. Homozygous: having two identical alleles of a gene. Heterozygous: having two different alleles of a gene. Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.
When the alleles of a pair are heterozygous, one may be dominant and the other recessive. The dominant allele is expressed and the recessive allele is masked. This is an example of complete dominance.hare. By Regina Bailey. Definition: An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. These DNA codings determine distinct traits that can be passed on from parents to offspring through sexual reproduction.