The word homozygous is used to describe a person who inherited two identical alleles for a particular trait. Many genes have two or more differing forms (such as eye color or hair texture) which are called alleles. When a person inherits two of the same alleles for a trait they are said to be homozygous for the trait (with homo meaning the same). When a gene is recessive (like the one for red hair) a person has to be homozygous for the trait for it to be expressed. If both parents had brown hair with the recessive gene for red hair (Br) their child would have to inherit both recessive genes and be homozygous for the trait in order to have red hair (rr).

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