Homozygous: Definition, Examples, Effects of Homozygous Genes, Differences and Homozygous Mutations

It refers to having identical alleles for a single trait.

An allele represents a particular form of a gene. Alleles can exist in different forms and diploid organisms typically have two alleles for a given trait.

These alleles are inherited from the parents during the gestation process. After fertilization , alleles join randomly as homologous chromosomes join.

The chromosomal structure is made up of 23 chromosomal pairs, of which 1 represents the sex of the individual.

One chromosome in each pair is donated by the mother and the other by the father. The alleles on these chromosomes determine traits or characteristics in the organism.

Homozygous alleles are categorized into two types, dominant and recessive. A homozygous dominant allele combination contains two dominant alleles and expresses the dominant phenotype (expressed physical trait).

A combination of homozygous recessive alleles contains two recessive alleles and expresses the recessive phenotype.

Homozygous example

The gene for seed shape in pea plants exists in two forms, one representing the allele for the round seed shape (R) and the other for the wrinkled seed shape (R).

The round shape of the seed is dominant and the wrinkled shape of the seed is recessive. A homozygous plant contains any of the following alleles for the seed shape: (RR) or (rr).

The genotype (RR) is homozygous dominant and the genotype (rr) is homozygous recessive for the shape of the seed.

The inheritance pattern of the offspring results in a 1: 2: 1 genotype ratio.

About 1/4 will be homozygous dominant for round seed shape (RR), 1/2 will be heterozygous for round seed shape (Rr), and 1/4 will have homozygous recessive wrinkled seed shape (rr) . The phenotypic ratio in this cross is 3: 1.

About 3/4 of the offspring will have round seeds and 1/4 will have wrinkled seeds.

In conclusion, homozygous is a word that refers to a particular gene that has identical alleles on both homologous chromosomes. It is mentioned with two uppercase letters (XX) for a dominant trait and two lowercase letters (xx) for a recessive trait.

Effects of homozygous genes

The following are some examples of homozygous genes:

The dominant trait for eye color is brown, represented by BB. All other eye colors – blue, gray, green, and hazel – are recessive traits, represented by bb.

A homozygous brown-eyed person would have the BB gene, while a homozygous blue-eyed person would have the bb gene.

A person is immune to poison ivy, which is represented by the dominant PP trait; while another is not immune to poison ivy, which is represented by the recessive trait distinguished by the symbol pp.

Freckles are the dominant feature of melanin deposits on the cheeks and body. A homozygous freckled person would have the FF gene, while someone with the homozygous gene from the individual without freckles would be represented by ff.

A full head of hair is a dominant feature, with the HH gene homozygous. However, the recessive trait (baldness) can manifest in an individual with the homozygous recessive or hh gene.

An individual has the dominant SS gene, a homozygous gene that causes hyperopia. However, your family member or acquaintance has the homozygous ss gene for the recessive trait, which is normal sight.

A girl’s blood clots normally, so her homozygous gene is the dominant CC. One boy in your class has hemophilia, which is present in the recessive cc gene.

Having dimples on the cheeks is a dominant trait, and the homozygous DD gene causes them. However, the recessive trait is distinguished by the symbol dd; people with this homozygous gene will not have freckles.

Curly hair is a dominant trait, with the homozygous HH gene causing the disease. Its recessive trait, represented by the homozygous hh gene, is straight hair.

The dominant trait for hearing and speaking is being able to speak normally, which is the result of the homozygous SS gene. However, an individual with the homozygous recessive trait, ss, cannot speak or hear properly and is instead deaf and dumb.

An individual has normal vision due to the homozygous VV gene. On the other hand, your partner possesses the recessive vv gene, resulting in color blindness.

A gentleman can bend his joints in a fun way because he possesses the dominant JJ ​​gene for double jointing. Another gentleman does not possess this gene; Instead, you have the recessive jj gene, which means your joints bend normally.

A child is born with an extra finger on each hand due to the dominant EE gene, while another newborn with the homozygous ee recessive gene has the normal number of fingers on their hands.

Detached earlobes are a trait that is the result of a dominant UU gene, whereas an individual with the homozygous recessive (uu) gene actually has attached earlobes.

Homozygous vs. Heterozygous

A monohybrid cross between a parent who is homozygous dominant and a parent who is homozygous recessive for a particular trait produces offspring that are all heterozygous for that trait.

These people have two different alleles for that trait. While individuals who are homozygous for one trait express one phenotype, heterozygous individuals can express different phenotypes.

In cases of genetic dominance in which complete dominance is expressed, the phenotype of the heterozygous dominant allele completely masks the recessive allele phenotype.

If the heterozygous individual expresses incomplete dominance, one allele does not completely mask the other, resulting in a phenotype that is a mixture of the dominant and recessive phenotypes.

If the heterozygous offspring express co-dominance, both alleles will be fully expressed and both phenotypes will be observed independently.

Homozygous mutations

Organisms can undergo changes in the DNA sequences of their chromosomes. These changes are called mutations.

In case of identical genetic mutations in both alleles of homologous chromosomes, the mutation is considered a homozygous mutation.

If the mutation occurs on only one allele, it is called a heterozygous mutation. Homozygous gene mutations are known as recessive mutations. For the mutation to be expressed in the phenotype, both alleles must contain abnormal versions of the gene.