Homozygous vs Heterozygous-Definition, 10 Differences, Examples

Key Differences Homozygous vs Heterozygous Overview

Homozygous Definition

A person who is homozygous has identical gene pairs inherited from each parent, which is a genetic condition.

  • Homozygous chromosomes may include dominant or recessive alleles for both alleles.
  • The recessive characteristic is denoted by two lowercase letters, while the dominant trait is represented by two capital letters (XX), (xx).
  • In contrast to homozygous-recessive chromosomes, which contain two copies of the allele coding for the recessive trait, homozygous-dominant chromosomes carry two copies of the allele coding for the dominant trait.
  • Only while each chromosome has a dominant gene at a similar locus, will the gene be dominant. Can dominant traits in homozygous creatures manifest
  • True breeding techniques guarantee that organisms are homozygous for all consistent traits.
  • Homozygous chromosomes arise as a consequence of asexual reproductive techniques like parthenogenesis. This makes sure that the phenotypic traits of the kids are the same as those of their parents.
  • The majority of the time, the presence of homozygosity is determined at a particular locus where identical copies of the gene impacting a characteristic are present on the two reciprocally homologous chromosomes.
  • Homozygotes are another name for homozygous cells or organisms. 
  • Sequence similarities between the nucleotides and the proteins that homozygous chromosomes’ genes code for are easily discernible.
  • Numerous genes have homozygous chromosomes, such as the genes for eye colour, where brown is the dominant phenotype and is represented by the letter BB in homozygous creatures.
  • When the recessive genotype in a homozygous-recessive genotype is a faulty gene, homozygosity may result in a number of illnesses.
  • Homozygous genotypes are associated with diseases such as cystic fibrosis, sickle cell anaemia, as well as phenylketonuria.

Heterozygous Definition

A person who is heterozygous has two distinct alleles of the same gene that they inherited from each parent.

  • Heterozygosity is shown in a diploid organism when a gene has two distinct alleles at a given locus.
  • The two alleles in heterozygous chromosomes are different, and the genotypes of heterozygotes are represented by a capital letter for the dominant allele and a lowercase letter for the recessive allele, such as Bb for eye colour.
  • Only the characteristic encoded by the dominant allele is expressed in heterozygous chromosomes when genes have qualities that are exhibited via total dominance.However, the expression of genes is more challenging in complex dominance models.
  • The phenotypic characteristics seen in partial dominance lie halfway between dominant and recessive traits. Similar to co-dominance, individual alleles express the phenotype in several bodily regions.
  • In comparison to homozygous dominant or homozygous recessive genotypes, the heterozygous genotype is substantially more fit. This level of fitness is known as “hybrid vigour.”
  • The majority of the time, heterozygous features exist in organisms that reproduce sexually.
  • Sexual reproduction techniques lead to the creation of heterozygous chromosomes. This makes sure that the phenotypic traits of the children are distinct from those of their parents.
  • Typically, the location where the copies of the gene controlling a characteristic present on the two reciprocally homologous chromosomes are different is where heterozygosity is characterised.
  • Heterozygotes are another name for heterozygous cells or organisms.
  • Certain heterozygous genotypes, such as homozygous genotypes, are typically connected to genetic diseases.
  • When the mutated allele is dominant, only the mutant copy may result in the illness. Dominant-disease is the name given to this illness.
  • When the mutant allele is recessive, the organism will act as a carrier and the disease will not show itself.
  • Heterozygous genotypes are linked to conditions such as familial hypercholesterolemia, Marfan’s syndrome, and Huntington’s disease.


Key Differences (Homozygous vs Heterozygous)
Basis for Comparison Homozygous Heterozygous
Definition Homozygous is a genetic condition where an individual inherits the same alleles of a gene from both the parents. Heterozygous is a genetic condition where an individual inherits different alleles of a gene from the two parents.
Genotype representation Homozygous genotypes are represented as AA or aa for homozygous-dominant or homozygous-recessive conditions, respectively. Heterozygous genotypes are represented by Aa genotypes.
Phenotypes Two different phenotypes are possible with dominant or recessive homozygous conditions. The phenotype is mostly due to the dominant allele in the heterozygous condition.
Gametes Homozygous genotypes result in a single type of gamete. Heterozygous genotypes result in two different types of gametes.
Traits Homozygous genotypes produce the same traits over different generations. Heterozygous genotypes produce different traits over different generations.
Hybrid vigour The homozygous condition doesn’t show hybrid vigour. Heterozygous condition shows hybrid vigour.
Types Homozygous-dominant and homozygous-recessive are two types of homozygous conditions. The heterozygous condition can be expressed in three different ways; co-dominance, incomplete dominance, and complete dominance.
Also called Organisms or cells with the homozygous condition are termed as homozygotes. Organisms or cells with the heterozygous condition are termed as heterozygotes.
Observed in Homozygous genotypes are observed in animals reproducing by asexual means. Heterozygous genotypes are mostly seen in animals reproducing by sexual means.
Diseases Common diseases associated with the homozygous condition include fibrosis, sickle cell anemia, and phenylketonuria. Common diseases associated with the heterozygous condition include Huntington’s disease, Marfan’s syndrome, and familial hypercholesterolemia.

Examples of homozygous genotypes

Eye colour

  • Brown eye colour is the hereditary characteristic that predominates and is represented by the genotype BB.
  • Therefore, the genotype for eye colour in homozygous people will be BB or bb.
  • All other eye hues, including blue, green, and grey, are recessive features that can only be seen in homozygous-recessive (bb) individuals.
  • The eye colour genes at the loci of the two chromosomes should be similar if the genotype is homozygous.


  • Tiny skin patches called freckles are brought on by the melanin pigment.
  • The MC1R gene regulates the development of freckles, which is also a dominant characteristic.
  • Freckled individuals have a homozygous-dominant genotype, which expresses the dominant allele.
  • When the gene is homozygous-recessive, however, people do not get freckles.

Examples of heterozygous genotypes

Sickle-cell anaemia

  • The recessive trait that causes sickle-cell anaemia results in faulty blood cell formation.
  • Thus, the dominant phenotype is manifested in those with heterozygous genotypes, avoiding the sickle-cell anaemia disease.
  • Red blood cells become sickle-shaped in sickle-cell anaemia, which renders them tiny and unable to transport enough oxygen.
  • In this way, those with sickle-cell anaemia benefit from having the heterozygous genotype of the sickle-cell gene.

Curly hair

  • Only those with homozygous-recessive alleles have straight hair, since curly hair is the dominant characteristic.
  • The protein responsible for curly hair is encoded by this gene.
  • These people have wavy hair, which falls between curly and straight hair due to heterozygous genetics.
  • The phenotype displayed in this phenomenon, which is also known as partial dominance, falls between the recessive and the dominant categories.
  • Individuals with the heterozygous condition have straight or curly hair in total dominance.

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