Homozygous and heterozygous alleles

We know that two alleles (one from each parent) are passed on to the child.

If both the alleles are identical , they are called Homozygous alleles

• Homo → same
• Zygous → having genetic material.

If the two alleles are dissimilar , they are called Heterozygous alleles .

• Hetero → different
• Zygous → having genetic material.

For example - 

Let us consider the pod colour of pea plant.

• The two alleles produced are Green colour pods and Yellow colour pods .
• Green colour pods is the dominant trait and yellow colour pods is the recessive trait.
• So we will assign ‘G’ for the green pod and ‘g’ for the yellow pod .

1. HOMOZYGOUS DOMINANT

• If both the alleles are Dominant , the plant will have Homozygous Dominant alleles.
• Phenotype: Green colour pods
• Genotype: GG

2. HOMOZYGOUS RECESSIVE

• If both the alleles are Recessive , the plant will have Homozygous Recessive alleles.
• Phenotype: Yellow colour pods
• Genotype: gg

3. HETEROZYGOUS DOMINANT

• If one allele is Dominant and other allele is recessive, the plant has Heterozygous Dominant alleles.
• Phenotype: Green colour pods
• Genotype: Gg

NOTE - Remember, the dominant allele can produce its phenotype (trait expression) even in the presence of the other form of allele . 

Hence the heterozygous pair of alleles is called heterozygous dominant condition .