“Homozygous” and “heterozygous” describe the pairs of genes you inherited from your parents.
Each version or variation of a gene is called anallele.
You get one allele from each parent.
Illustration by Michela Buttignol for Verywell Health
Sometimes the alleles are identical and sometimes they are different.
When you inherit different alleles, the dominant allele is the one that is expressed in your body.
Because the brown hair allele is dominant, you will have brown hair.
This means there need to be two copies of the blonde hair allele for that trait to be expressed.
The Greek roothomo- means “same” and the prefixhetero-means “other” (different).
Azygoteis a cell created when two gametesin humans, a sperm and an eggcome together.
What Is a Gene?
Genesare very specific segments ofDNA (deoxyribonucleicacid).
Each of your cells contains very long stretches of DNA.
This is heritable material that you get from each of your parents.
DNA is composed of a series of individual components called nucleotides.
Genes are used by other machinery inside the cell to make specific proteins.
Specific genes in the body fulfill distinct roles.
For example,hemoglobinis a complex protein molecule that works to carry oxygen in the blood.
You inherit DNA from your parents.
Half of your DNA comes from your mother and the other half from your father.
For most genes, you inherit one copy from your mother and one from your father.
Alleles, however, have variations in the sequence of nucleotides in specific genes.
For example, one allele might begin with the sequence ATTGCT, and another might begin ACTGCT instead.
Sometimes these variations dont make a difference in the end protein, but sometimes they do.
They might cause a small difference in the protein that makes it work slightly differently.
Heterozygous:You inherit a different version of a gene from each parent.
They do not match.
Disease Mutations
Many gene variations arent a big deal and just contribute to normal human variation.
However, gene variations can lead to human diseasethese are consideredmutations.
Homozygous traits, such as blue eyes or red hair happen when normal genes are passed down.
If you inherit mutated alleles, it can lead to homozygous genetic diseases.
This clogs the airways and blocks the secretion of digestive enzymes.
Without treatment, people with PKU can develop issues including seizures, psychiatric disorders, and behavioral problems.
Heterozygous Genetic Diseases
you’re free to sometimes get genetic diseases if you have heterozygous genes.
In some types ofgenetic diseases, heterozygous genes almost always cause the disease.
For recessive diseases, like sickle cell anemia, a person with heterozygous genes would not get the disease.
However, sometimes they may have other subtle changes, depending on the disease.
Marfan’s Syndrome
Marfans syndromeis caused when the FBN1 gene is altered.
This gene is needed to make a protein called fibrillin.
Alteration causes a decreased production of fibrillin, resulting in parts of the body stretching abnormally when stressed.
Familial Hypercholesterolemia
due to gene mutations,familialhypercholesterolemiaaffects how your body processeslow-density lipoprotein (LDL) cholesterol.
What About Sex Chromosomes?
Sex chromosomes are the X and Y chromosomes that play a role in gender differentiation.
Women inherit two X chromosomes, one from each parent.
So a female can have a homozygous or heterozygous pattern of genes for any trait on the X chromosome.
Men inherit two different sex chromosomes: X and Y.
Inheritance
Lets assume two versions of a gene: A and a.
When two people have a child, there are several possibilities.
Summary
Genes are segments of DNA that determine our traits.
Your biological mother and father each contribute half of your genetic makeup.
The science of genetics is complex.
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