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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 .

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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Economics, Accounting and English at Teachoo