Dominance (genetics)

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Dominance in genetics is a relationship between two variant forms (alleles) of a single gene, in which one allele masks the expression of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms (B & b), three combinations of alleles (genotypes) are possible: BB, Bb, and bb. If Bb individuals (heterozygotes) show the same form of the trait (phenotype) as BB individuals (homozygotes), and bb homozygotes show an alternative phenotype, allele (B) is said to dominate or be dominant to allele (b), and (b) is said to be recessive to (B).

Contents

Background: diploid, chromosomes, genes, loci, & alleles

Diploid / haploid

Most familiar plants, like peas, and familiar animals, like fruit flies and humans, have paired chromosomes, and are described as diploid. One chromosome of each pair is contributed by each parent, one by the female parent in her ova, and one by the male parent in his sperm, which are joined at fertilization. The ova and sperm cells have only one copy of each chromosome and are described as (haploid). Production of haploid gametes occurs through a cell division process called meiosis.

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