What is the difference between homozygous and heterozygous?

Homozygous and heterozygous describe the combination of alleles an organism has for a particular gene.

Homozygous refers to having two identical alleles for a gene.
Heterozygous refers to having two different alleles for a gene.

Key differences:

• Allele combination:
  Homozygous: same alleles (TT or tt)
  Heterozygous: different alleles (Tt)

• Types:
  Homozygous can be:

  • Homozygous dominant (TT)

  • Homozygous recessive (tt)

• Expression of traits:
  Homozygous shows a single trait clearly; heterozygous usually expresses the dominant trait.

• Genetic variation:
  Homozygous has less variation; heterozygous contributes to genetic diversity.

• Example:
  For plant height:
  TT → tall (homozygous dominant)
  tt → short (homozygous recessive)
  Tt → tall (heterozygous)

In simple terms: Homozygous means having identical alleles, while heterozygous means having different alleles for a trait.