Ruth Jessen Hickman, MD, is a freelance medical and also health writer and published publication author." data-inline-tooltip="true">Ruth Jessen Hickman, MD

Dept that Clinical Cytogenics, Addenbrookes Hospital / Science photo Library / Getty images

What Is a Gene?

Before specifying homozygous and heterozygous, we have actually to first think around genes. Each of her cells contains really long follow me of DNA (deoxyribonucleic acid). This is heritable material that you acquire from each of your parents.

You are watching: What is the difference between heterozygous and homozygous individuals?

Inside the cell, DNA is usually found bundled up into chromosomes (found in 23 different pairs).

Genesare very particular segments of DNA with a unique purpose. This segments are supplied by other machinery inside the cabinet to make certain proteins. Proteins are the structure blocks supplied in many vital roles inside the body, consisting of structural support, cabinet signaling, chemistry reaction facilitation, and also transport.

The cell renders protein (out of its structure blocks, amino acids) by analysis the sequence of nucleotides found in the DNA. The cell supplies a sort of translation mechanism to use information in the DNA to build details proteins with particular structures and also functions.

You inherit DNA from her parents. Broadly speaking, half of her DNA originates from your mother and also the other half from her father. For many genes, girlfriend inherit one copy from her mother and also one from your father.

However, over there is an exemption involving a particular pair that chromosomes called sex chromosomes. Due to the fact that of the way sex chromosomes work, males only inherit a single copy of particular genes.

variations in gene

The genetic code of human beings is fairly similar: fine over 99 percent that nucleotides that are part of genes are the same throughout all humans. However, there room some sport in the succession of nucleotides in details genes.

For example, one sports of a gene might begin with the succession ATTGCT, and also another variation might start ACTGCT instead. These different variations of genes are dubbed alleles.

Sometimes these variations don’t do a distinction in the end protein, however sometimes lock do. Lock might cause a tiny difference in the protein that renders it work slightly differently.

A human is said to it is in homozygous because that a gene if they have two identical copies of the gene. In our example, this would certainly be two duplicates of the variation of the gene beginning “ATTGCT” or two duplicates of the version beginning “ACTGCT.”

Homozygous: You inherit the exact same version of the gene from every parent, therefore you have actually two corresponding genes.

Heterozygous: You inherit a various version that a gene from each parent. They carry out not match.

condition Mutations

Many of this mutations aren’t a large deal and also just contribute to normal person variation. However, other particular mutations deserve to lead to human disease. That is regularly what world are talking about when they mention “homozygous” and also “heterozygous”: a specific form of mutation the can cause disease.

One instance is sickle cabinet anemia. In sickle cell anemia, there is a mutation in a solitary nucleotide that reasons a readjust in the nucleotide that a gene (called β-globin gene).

Generally speaking, there room three various possibilities:

Someone is homozygous because that the typical β-globin gene (has two normal copies)Someone is heterozygous (has one normal and also one abnormal copy)Someone is homozygous because that the abnormal β-globin gene (has 2 abnormal copies)

People who room heterozygous for the sickle cell gene have actually one unaffected copy the the gene (from one parent) and one influenced copy the the gene (from the other parent).

These civilization usually don’t acquire the symptoms of sickle cell anemia. However, civilization who space homozygous because that the abnormal β-globin gene do gain symptoms that sickle cell anemia.

Heterozygotes and also Genetic illness

Heterozygotes can gain genetic disease, yet it counts on the kind of disease. In some varieties of genetic diseases, a heterozygous individual is almost specific to acquire the disease.

In illness caused by what are called leading genes, a human needs just one poor copy the a gene to have problems. One instance is the neurological disorder Huntington’s disease.

A human being with only one impacted gene (inherited from either parent) will certainly still nearly certainly gain Huntington's disease as a heterozygote. (A homozygote who receives two abnormal copies of the disease from both parental would likewise be affected, however this is less common for dominant an illness genes.)

If a leading gene causes a disease, a heterozygote may manifest the disease. If a recessive gene causes a disease, a heterozygote may not build the condition or may have lesser results of it.

What around Sex Chromosomes?

Sex chromosomes are the X and Y chromosomes that play a function in gender differentiation. Ladies inherit 2 X chromosomes, one from every parent. For this reason a female deserve to be considered homozygous or heterozygous about a particular trait on the X chromosome.

Men space a little an ext confusing. They inherit two various sex chromosomes: X and also Y. Because these two chromosomes are different, the state “homozygous” and also “heterozygous” don’t apply to these two chromosomes top top men.

You may have heard of sex-linked diseases, prefer Duchenne muscular dystrophy. These display a different inheritance sample than typical recessive or dominant conditions inherited with the various other chromosomes (called autosomes).

Heterozygote benefit

For some condition genes, it is possible that being a heterozygote offers a person certain advantages. For example, that is assumed that gift a heterozygote for the sickle cell anemia gene may be somewhat protective because that malaria, in comparison for to people who don’t have an abnormal copy.


Let’s assume 2 versions that a gene: A and a. When two world have a child, there are several possibilities:

Both parents room AA: every one of their kids will be AA as well (homozygous for AA).Both parents space aa: every one of their children will be aa too (homozygous for aa).One parent is Aa and also another parental is Aa: your child has actually a 25 percent possibility of gift AA (homozygous), a 50 percent chance of gift Aa (heterozygous), and a 25 percent chance of gift aa (homozygous)One parental is Aa and also the various other is aa: your child has a 50 percent chance of being Aa (heterozygous) and also a 50 percent chance of being aa (homozygous).

See more: "Brothers, What We Do In Life Echoes In Eternity, 'What We Do In Life, Echoes In Eternity'

One parental is Aa and the various other is AA: their child has actually a 50 percent chance of being AA (homozygous) and a 50 percent possibility of being Aa (heterozygous).