Genetic inheritance works by each person getting two alleles for each gene, one from each parent. Homozygous people have two of the same alleles, either both dominant or recessive. For example, brown eye color is homozygous dominant, shown as BB.
Heterozygous people, on the other hand, have one dominant and one recessive allele for a gene.
Examples of Homozygous and Heterozygous Traits
Homozygous and heterozygous genotypes affect many traits and genetic disorders. Let’s look at some examples that show how these genetic combinations impact our lives.
Eye Color
Eye color is a clear example of how genotypes influence a visible trait. Brown eye color is dominant, while blue and green are recessive. If someone has two dominant alleles, they’ll have brown eyes. If they have one dominant and one recessive allele, they’ll also have brown eyes.
But, if they have two recessive alleles, they’ll have blue or green eyes. This depends on the specific alleles they have.
Blood Type
Blood type is another trait influenced by inherited alleles. The ABO blood group system has three alleles: A, B, and O. The A and B alleles are codominant, while O is recessive. Here’s how genotypes relate to blood types:
| Genotype | Blood Type |
|---|---|
| AA or AO | A |
| BB or BO | B |
| AB | AB |
| OO | O |
Sickle Cell Anemia
Sickle cell anemia is caused by a homozygous recessive genotype. People with two sickle cell alleles (HbS) from their parents will have the disorder. It affects red blood cells’ shape and function.
Those with one sickle cell allele (HbA/HbS) are carriers. They usually don’t have symptoms.
Other disorders like cystic fibrosis, phenylketonuria, Huntington’s disease, and Marfan syndrome are also influenced by these genotypes. People with a homozygous recessive genotype often develop the disorder. Those with a heterozygous genotype may be carriers or have milder symptoms.
Mendel’s hybridization experiments showed that diploid organisms can have two genetic copies. These copies may encode different versions of a characteristic.
