Homozygous describes the genetic makeup of a cell or organism where there are two identical versions of a gene at a particular locus (location on a chromosome). This means that an individual inherits the same version of a gene from both their mother and father.
Understanding Homozygous Genotypes
A homozygous genotype means the two alleles (gene versions) are the same. The reference states that a homozygous genotype (HOH-moh-ZY-gus JEE-noh-tipe) is "a term that describes having two identical versions of the same gene (one inherited from the mother and one inherited from the father)."
Here's a breakdown:
Types of Homozygous Genotypes
- Homozygous Dominant: This occurs when both alleles are dominant. For instance, if "B" represents the dominant allele for brown eyes, an individual with a BB genotype would be homozygous dominant. This individual will express the dominant trait.
- Homozygous Recessive: This happens when both alleles are recessive. For instance, if "b" represents the recessive allele for blue eyes, an individual with a bb genotype would be homozygous recessive and express the recessive trait.
Key Aspects of Homozygous Genotypes
| Feature | Description |
|---|---|
| Gene Versions | Two identical versions of the same gene. |
| Inheritance | One version is inherited from each parent. |
| Expression | Both alleles are either normal or both carry the same mutation. |
| Dominant Example | Two copies of a dominant allele (e.g., BB for brown eyes). |
| Recessive Example | Two copies of a recessive allele (e.g., bb for blue eyes). |
Examples
- Eye Color: If a gene determines eye color and an individual receives the allele for blue eyes from both parents, they will be homozygous recessive for that gene and have blue eyes.
- Disease: In some genetic disorders, an individual needs to be homozygous recessive (carrying two copies of a specific gene mutation) to express the disease.
How Homozygous Genotypes Impact Traits
The main impact of a homozygous genotype is that it directly dictates what version of the trait is expressed by the individual, since both copies of the gene are the same.
Conclusion
In summary, being homozygous simply means having two copies of the same allele for a specific gene. These can be two dominant alleles or two recessive alleles.
