# Allele --- An **allele** is a particular version of a [[gene]] that are found on [[homologous pair|homologous]] chromosomes. These can match, or they can be different, depending on the genetic makeup of the organism. For example, a human may have one allele for brown eyes, and one for blue on the same chromosome. ## Zygosity **Zygosity** describes [[ploidy|diploid]] chromosomes and whether or not their alleles are matching. **Homozygous** genes have two matching alleles. **Heterozygous** genes have two disperate alleles. **Hemizygous** genes are also called X-linked, as they live on the X chromosome. (Does this only happen in males?) ![[zygosity.png]] ## Allele Interaction (Dominance and Recession) Some alleles may be more or less [[dominance and recession|dominant]] than others. **Linkage** is the tendancy of alleles of a particular gene to be inherited together, because they are located close together on their chromosome. A **null allele** also called a "loss-of-function" allele, are alleles that do not work. ___