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
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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