What is the Difference between Homozygous and Heterozygous

In genetics, homozygous and heterozygous terms are used frequently to explain the genetic makeup of the studied organism. So, it is very important to study the difference between homozygous and heterozygous.

Homozygous

Homozygous is a genetic combination in which both alleles of a gene for a particular trait in a diploid organism are identical. Such organisms are called homozygotes. Homozygous can be recessive (aa) or dominant (AA), so we can observe two distinct phenotypes in pure breeds. Same letters are used when representing the alleles for homozygous.

Example of homozygous

In Mendel’s experiment, he used seven traits of pea plant. The pure breeds which he used were homozygous for that particular traits. For example, round seeds (RR) and wrinkle seeds (rr) in parental generation were homozygous. Similarly, yellow seeds (YY) and green (yy) seeds were also homozygous in parental generations.

Heterozygous

Heterozygous is a genetic combination in which both alleles of a gene for a particular trait in a diploid organism are different. Such organisms are called heterozygotes. Heterozygous shows hybrid effects, so we need to perform test cross to check homozygosity or heterozygosity of an organism. Heterozygous can show complete dominance, incomplete dominance and codominance. Different letters are used when representing the alleles for heterozygous.

Example of heterozygous

In Mendel’s experiment, round seeds in first filial generation were heterozygous when two pure breeds i.e., round seeds and wrinkle seeds plants were crossed with each other. Moreover, yellow seeds obtained during first filial generation were also heterozygous.

What is the difference between homozygous and heterozygous

The main difference between homozygous and heterozygous are listed in the table below.

Homozygous

Heterozygous

A genetic makeup that consists of two identical alleles of a gene for a trait in a diploid organism

A genetic makeup that consists of two different alleles of a gene for a trait in a diploid organism.

Genotypes can be written as AA or aa

Genotype can be written as Aa

Produces single type of gametes

Produces two types of gametes

Two phenotypes are expressed

One phenotype is expressed

Self-breeding produces the same trait over the generations

Self-breeding produces a combination of different traits

Do not show extra effects

shows hybrid effects

Present in true breeds

Present in cross breeds

Homozygous dominant and Homozygous recessive are the two types

Complete dominance, incomplete dominance and codominance are the types

Example: Round seeds (RR) and wrinkled seeds (rr) of P1 generation

Example: Round seeds (Rr) of F1 generation





















Diagram of difference between homozygous and heterozygous

what is the difference between homozygous and heterozygous

Video lesson on difference between homozygous and heterozygous

Some questions and answers

1. Define homozygous

A. Homozygous is a genetic combination in which both alleles of a gene for a particular trait in a diploid organism are identical.

2. Define homozygous

A. Heterozygous is a genetic combination in which both alleles of a gene for a particular trait in a diploid organism are different.

3. State two differences between homozygous and heterozygous

A. Homozygous is a genetic makeup that consists of two identical alleles of a gene for a trait in a diploid organism. While, heterozygous is a genetic makeup that consists of two different alleles of a gene for a trait in a diploid organism.

4. How many homozygous alleles are there?

A. Homozygous can be dominant (AA) or recessive (aa).

5. How do you know if its homozygous dominant or heterozygous?

A. Test cross can be used to determine to check homozygosity or heterozygosity of an organism.

6. Give example of heterozygous and homozygous

A. Round seeds (RR) and wrinkled seeds (rr) of P1 generation of pea plant. Round seeds (Rr) of F1 generation of pea plants.



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