what is homozygous recessive

A homozygous recessive genotype means an organism has two recessive alleles for a gene, often written with two lowercase letters like aa or tt. Because there is no dominant allele present, the recessive trait is expressed.

Quick Scoop

• Homozygous means the two alleles are the same.

• Recessive means the trait only shows when both alleles are recessive.

• Example: if t means short plants, then tt is homozygous recessive and the plant shows the short trait.

Simple example

If a gene has:

• A = dominant allele
• a = recessive allele

Then:

• AA = homozygous dominant
• Aa = heterozygous
• aa = homozygous recessive

Why it matters

Some genetic conditions or traits appear only in the homozygous recessive form, meaning a person or organism must inherit the recessive allele from both parents for the trait to show. Examples mentioned in the sources include cystic fibrosis and sickle cell anemia.

If you want, I can also show this with a Punnett square.