Homozygous

Homozygous describes the genetic condition or the genetic state where an individual has inherited the same DNA sequence for a particular gene from both their biological mother and their biological father. Homozygous allele may be dominant or recessive. An allele is a version of a gene that affects the functionality of the protein produced by the gene. A homozygous dominant allele combination contains two dominant alleles and expresses the dominant phenotype (expressed physical trait). A homozygous recessive allele combination contains two recessive alleles and expresses the recessive phenotype. The alleles are represented by two capital letters (XX) for a dominant allele and two lowercase letters (xx) for a recessive allele.

The dominant eye color brown which is determined by the genotype BB, the recessive eye color hazel, which is determined by genotype bb and the human blood type O, which is determined by the genotype OO are example of homozygous traits.

What You Need To Know About Homozygous

Homozygous is the presence of two copies of the same allele which codes for a particular trait.
The two types of homozygous alleles are homozygous-dominant and homozygous-recessive.
Homozygous individuals can carry either dominant or recessive allele pairs of a gene but not both (Example: TT or tt).
Homozygous individuals are pure as a trait and give rise to similar genotypes.
Homozygous individual or organism produces one type of gametes.
Does not exhibit extra vigour.
Self-breeding of homozygous individuals produces the same trait over generations.
Diseases that occur in the homozygous condition include sickle-cell anemia and some cases of steroid-resistant nephrotic syndrome.
Examples of homozygous: The dominant eye color brown which is determined by the genotype BB, the recessive eye color hazel, which is determined by genotype bb and the human blood type O, which is determined by the genotype OO.

Heterozygous

Homozygous is the presence of both dominant and recessive alleles in the allele pair, which determines a particular trait of a diploid organism. The alleles are represented by one capital letter and one lower case letter (Xx). The expression means that the two alleles in the pair are different from each other. The inheritance of heterozygous alleles can happen in three ways, that is, dominance, incomplete dominance and codominance.

In dominance, both alleles in the heterozygous pair are expressed. The AB blood group is a good example of codominance, whereby both antigen A and antigen B are independently expressed in the red blood cells.

In incomplete dominance, one allele is not completely dominant over the other. Here, a combination of phenotypes can be observed in the offspring for example in snapdragon flower where the dominant flower color is red and the recessive flower color is white.

In complete dominance, one allele is completely dominant over the other. Here, only the dominant allele is expressed and it determines the phenotype of the individual.

What You Need To Know About Heterozygous

Heterozygous is the presence of two different copies of alleles of a particular gene.
The three types of heterozygous alleles are complete dominance, incomplete dominance and codominance.
Heterozygous individual has both dominant and recessive allele pair of a gene (Example: Tt).
Heterozygous individual is not often pure and produces offspring with different genotypes.
Heterozygous individual produces two types of gametes.
Can exhibit extra vigor referred to as hybrid vigour or heterosis.
Self-breeding of heterozygous individual produces a combination of different traits.
Illness that can occur in heterozygous condition include Huntington’s disease.
Examples of heterozygous: The snapdragon flower color, codominance of the hair color in roan horses and the human blood type AB which is determined by the genotype AB.

Also Read: Difference Between Genotype And Phenotype

Difference Between Homozygous And Heterozygous In Tabular Form

BASIS OF COMPARISON	HOMOZYGOUS	HETEROZYGOUS
Description	Homozygous is the presence of two copies of the same allele which codes for a particular trait.	Heterozygous is the presence of two different copies of alleles of a particular gene.
Types	The two types of homozygous alleles are homozygous-dominant and homozygous-recessive.	The three types of heterozygous alleles are complete dominance, incomplete dominance and codominance.
Gene	Homozygous individuals can carry either dominant or recessive allele pairs of a gene but not both (Example: TT or tt).	Heterozygous individual has both dominant and recessive allele pair of a gene (Example: Tt).
Nature	Homozygous individuals are pure as a trait and give rise to similar genotypes.	Heterozygous individual is not often pure and produces offspring with different genotypes.
Gametes	Homozygous individual or organism produces one type of gametes.	Heterozygous individual produces two types of gametes.
Extra Vigour	Does not exhibit extra vigour.	Can exhibit extra vigour referred to as hybrid vigour or heterosis.
Self-breeding	Self-breeding of homozygous individuals produces the same trait over generations.	Self-breeding of heterozygous individual produces a combination of different traits.
Illness	Diseases that occur in the homozygous condition include sickle-cell anemia and some cases of steroid-resistant nephrotic syndrome.	Illness that can occur in heterozygous condition include Huntington’s disease.
Examples	The dominant eye color brown which is determined by the genotype BB, the recessive eye color hazel, which is determined by genotype bb and the human blood type O, which is determined by the genotype OO.	The snapdragon flower color, codominance of the hair color in roan horses and the human blood type AB which is determined by the genotype AB.

Similarities Between homozygous and heterozygous

Both heterozygous and homozygous alleles can be found at the locus of homozygous chromosome.
Both are terms used to describe the genotype of a diploid organism.

Also Read: Difference Between Dominant And Recessive Genes