Difference Between Homozygous and heterozygous is that A homozygous individual is one who has two equal alleles of a gene. A heterozygous individual is one who has different alleles for a particular characteristic. When we talk about homozygous or heterozygous we mean a gene for a specific character. Thus, an individual can be homozygous for one gene and heterozygous for another.
The genes are DNA fragments that determine a specific character of the living being. A gene for a character can have several versions, which is known as alleles. For example, the gene for the color of rabbit fur (gene C) has four different alleles: brown allele, albino allele, chinchilla allele, and the Himalayan allele. However, a rabbit may only have two alleles.
In fertilization, a female sex cell or ovule and a male sex cell (sperm) join together and form a cigar with the total genetic load of the species. An individual receives a gene from the father and a gene from the mother for the same character, that is, has two alleles for the same trait. In humans, there are approximately 21 thousand different genes.
| Homozygous | Heterozygous | |
|---|---|---|
| Definition | It has two equal alleles of a gene | It has two different alleles of a gene |
| Origin of the alleles | From the parents | From the parents |
| Types |
| – |
| Examples | The albino color in the skin of some animals in a homozygous character | People with AB blood type are heterozygous |
When the alleles of a gene are equal, it is spoken of a homozygous individual. In the case of rabbits, if a rabbit receives the two brown alleles it will be homozygous for the brown color, and if it has two albino alleles, it will be homozygous for the albino color.
When two equal alleles are combined that express the dominant phenotype, we are in front of a dominant homozygote. For example, the brown color of the eyes in humans is a dominant character, if the person has both alleles for brown, it will be homozygous dominant.
There are certain combinations of alleles that can only be expressed when they are homozygous. This is found in recessive alleles, versions of genes that are not expressed when there is another dominant gene. For example, in the ABO blood group in humans, the O allele is recessive. This means that people with blood type O are homozygous, they have two alleles O (OxO).
When the two copies of the gene that are inherited from the parents are different, the individual is said to be heterozygous for that gene. Following the example of the color of the fur of rabbits, when a rabbit has a brown allele and an albino allele, the rabbit will be heterozygous for the color brown.
In the case of humans, the type of ABO blood group in red blood cells is also a good example to explain when a character is homozygous or heterozygous. The gene for the blood group has three alleles: A, B and O. A person can inherit the following allele combinations from his parents:
| Allele combination | Blood type | Character |
|---|---|---|
| AxA | TO | homozygous |
| AxO | TO | heterozygous |
| BxB | B | homozygous |
| BxO | B | heterozygous |
| Axb | AB | heterozygous |
| OxO | OR | homozygous |
The combination of alleles would be the genotype and the blood group is the phenotype. Whenever we see that the alleles are equal (AxA, BxB, OxO) they are homozygous, and when they are different (AxO, BxO, AxB) they are heterozygous.
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