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Homozygous Vs Heterozygous: Definition, Differences, Examples

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Homozygous Definition

Homozygous is a genetic situation in which a person inherits the same alleles from both parents for a gene.

  • Both alleles are dominant or recessive in homozygous chromosomes. Two capital letters (XX) denote the dominant trait, while two lowercase letters denote the recessive trait (xx).
  • Homozygous-dominant chromosomes have two copies of the dominant allele, while homozygous-recessive chromosomes have two copies of the recessive allele.
  • The dominant trait is only expressed in homozygous organisms when both chromosomes have a dominant gene at the same location.
  • True breeding processes ensure that organisms are homozygous for all qualities that are held constant.
  • Asexual reproductive methods, such as parthenogenesis, produce homozygous chromosomes. This ensures that the offspring’s phenotypic characteristics are identical to those of their parents.
  • Homozygosity is usually defined as the presence of identical copies of a gene affecting a trait on the two reciprocal homologous chromosomes.
  • Homozygotes refer to homozygous cells or organisms.
  • In their nucleotide sequences and the proteins they code for, homozygous chromosomal genes show easily identifiable sequence similarities.
  • Homozygous chromosomes can be found in a variety of genes, such as eye colour genes, where the dominant characteristic is brown and appears as BB in homozygous creatures.
  • In a homozygous-recessive genotype where the recessive genotype is a defective gene, homozygosity may cause a variety of disorders.
  • Homozygous genotypes are linked to diseases such cystic fibrosis, sickle cell anaemia, and phenylketonuria.

Definition of Homozygous

Heterozygous Definition

Heterozygous is a genetic situation in which a person inherits distinct alleles of the same gene from both parents.

  • In a diploid organism, heterozygozygosity occurs when a gene includes two distinct alleles at the same gene locus.
  • The two alleles in heterozygous chromosomes are different, and heterozygous genotypes are indicated by a capital letter for the dominant allele and a lowercase letter for the recessive allele, such as Bb for eye colour.
  • Only the trait coded by the dominant allele is expressed in heterozygous chromosomes with genes that express traits via full dominance. The expression of genes is more complicated in complex dominance schemes.
  • The phenotypic trait found in partial dominance is halfway between dominant and recessive phenotypes. In co-dominance, phenotypes are expressed in distinct areas of the body by individual alleles.
  • Homozygous-dominant and homozygous-recessive genotypes have worse fitness than heterozygous genotypes. Hybrid vigour is the phrase used to describe this level of fitness.
  • Organisms that reproduce through sexual breeding are frequently heterozygous for the features that are different.
  • Heterozygous chromosomes are formed as a result of sexual reproduction methods. This ensures that the offspring’s phenotypic characteristics differ from those of their parents.
  • Heterozygosity is usually characterised at a specific locus where two reciprocal homologous chromosomes have differing copies of a gene that affects a trait.
  • Heterozygotes are cells or organisms that are heterozygous for both chromosomes.
  • Some heterozygous genotypes, like homozygous genotypes, are frequently linked to genetic disorders.
  • If the mutated allele is dominant, the disease is caused by only the mutated copy. This is referred to as dominant-disease.
  • The disease will not manifest if the mutant allele is recessive, and the organism will act as a carrier.
  • Heterozygous genotypes are linked to diseases like Huntington’s disease, Marfan’s syndrome, and familial hypercholesterolemia.

Difference Between Homozygous and Heterozygous (Homozygous vs Heterozygous)

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Homozygous Genotypes  Examples.

1 . The colour of your eyes

  • Brown is the most common genetic trait for eye colour, represented by the BB genotype.
  • Thus, the genotype for eye colour in homozygous people will be BB or bb.
  • All other eye colours, from blue to green to grey, are recessive features that manifest only when the genotype is homozygous-recessive, bb.
  • The genes for eye colour at the loci of the two chromosomes should be identical if the genotype is homozygous.

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2. Freckles

  • Freckles are little spots on the skin created by the pigment melanin.
  • The MC1R gene controls the formation of freckles, which is also a dominant trait.
  • Individuals with freckles have a homozygous-dominant genotype, which means the dominant allele is expressed.
  • Individuals with a homozygous-recessive genotype, on the other hand, do not develop freckles.

Heterozygous Genotypes Examples

1 . Sickle-cell anaemia (SCA) is a kind of anaemia that affect

  • Sickle-cell anaemia is caused by a recessive condition that causes blood cells to develop improperly.
  • As a result, the dominant phenotype is manifested in individuals with heterozygous genotypes, preventing sickle-cell anaemia.
  • In sickle-cell anaemia, the red blood cells’ structure changes to a sickle shape, making them tiny and unable to carry enough oxygen.
  • As a result, the heterozygous genotype of the gene that causes sickle-cell anaemia benefits such people.

2. Curly Hair

  • Because curly hair is the dominant trait, only those with homozygous-recessive alleles have straight hair.
  • The protein that promotes curly hair is coded for by this gene.
  • Individuals with a heterozygous genotype have wavy hair, which is a cross between curly and straight hair.
  • This is also known as partial dominance, because the phenotype displayed is somewhere between dominant and recessive.
  • Individuals with the heterozygous condition have curly hair straight in complete dominance.



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