Zygosity refers to the
genetic condition of a
zygote. In genetics, zygosity describes the similarity or dissimilarity of
DNA between homologous
chromosomes at a specific
allelic position or gene.Every gene in a diploid organism has two alleles at the gene's locus. These alleles are defined as
dominant or
recessive, depending on the phenotype resulting from the two alleles. If a gene's two alleles are both dominant or both recessive, that specific gene is homozygous. If one allele is dominant and the other is recessive, the gene is heterozygous. The terms homozygous, heterozygous and hemizygous are used to simplify the description of the
genotype of a
diploid organism at a single genetic
locus. At a given gene or position along a chromosome (a locus), the DNA sequence can vary among individuals in the population. The variable DNA segments are referred to as alleles, and diploid organisms generally have two alleles at each locus, one allele for each of the two
homologous chromosomes. Simply stated, homozygous describes two identical alleles or DNA sequences at one locus, heterozygous describes two different alleles at one locus, and hemizygous describes the presence of only a single copy of the gene in an otherwise diploid organism.
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Presence of two identical alleles at a locus in a diploid organism (see heterozygosity). It is the result of inheritance of identical alleles from both parents.