Homozygous (homozygote) a diploid organism or cell carrying the identical alleles of a gene in homologous chromosomes ( AA or aa ). In genetics, of a pair of chromosomes having, in the corresponding points, two identical genes. Consequently, the production of gametes equal to that character occurs.


Whenever the cell duplicates its genetic heritage, DNA condenses into chromosomes. The number and shape of these chromosomes for each species are almost constant and in all cells of the same organisms is equal.

In a homo-zygote, alleles at a locus are equal to alleles on the homologous chromosome.

Let’s come and dig into more detail.

In general, the alleles can be dominant or recessive. Therefore, the diploid individual can be respectively dominant or recessive homozygous.

Dominant and recessive homozygous

Dominant homozygote(AA) when an individual has, for a single gene, two equal dominant alleles; a dominant homozygote is phenotypically the same. Therefore, identification is more difficult. A dominant homozygous genotype arises when a given sequence spans two alleles for the dominant attribute (eg.AA ).

A homozygous recessive genotype arises when the sequence spans two alleles of the recessive attribute. It is a pair of double recessive genes at the same locus. When an individual has two equal recessive alleles for a single gene; a recessive homozygote has a unique phenotype. Therefore, immediately identifiable.

Since each individual compose of cells containing all the same genetic patrimony.

Now let’s talk about its example and diseases.

Examples and diseases of homozygous


The examples of homozygous are as follows:

  • The person is homozygous If a person doesn’t have freckles. Freckles mean tiny dots on the skin.
  • Eye color: The blue eye color is recessive and brown eye color is dominant. The person can have a brown eye color whether it is heterozygous or homozygous. For blue eye color, the two identical blue eye alleles need.
  • Hair color: The brown hair is dominant and red hair is a recessive trait. The children have red hair and will be homozygous if they inherit the recessive allele.


Following are the diseases of homozygote which more effect people:

  • Sickle cell anemia
  • Phenylketonuria
  • Cystic fibrosis
  • Methylenetetrahydrofolate reductase (MTHFR) gene mutation

The inbreeding increases homozygosity, hence the increased occurrence of genetic disease in inbred societies.

Now let’s compare with other terms

Homozygous and heterozygous

A homozygous individual is one who has two equal alleles of a gene. It has only one variant of the allelic gene. Although this can be dominant or recessive. While a heterozygous individual is one who has different alleles for a certain characteristic. Heterozygotes have two variants of the allelic gene.

A homozygous individual is pure for a trait and contains both alleles that are similar in that trait at the gene locus. Although the heterozygous individual is not pure for the trait and most often has a dominant trait.



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