Question

Explain the following terms:

(a) heterozygous

(b) Homozygous

(c) pedigree chart.

Answer 1

(a) Heterozygous: The condition in which a pair of homologous chromosomes carries dissimilar alleles for a particular character.

For example -

(i) A daughter (XX^o) from a normal homozygous mother for colour vision (XX) and a colour blind father has one normal and one defective allele (X^oY).

(ii) Certain tongue rollers are heterozygous with Rr genotype.

(b) Homozygous: The condition in which a pair of homologous chromosomes carries similar alleles for a particular character.

For example -

(i) A colorblind daughter (X^oX^o) will have both the X chromosomes with defective alleles.

(ii) A non-roller will have rr (homozygous) genotype.

(c) Pedigree Chart: A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next. In the pedigree chart, males are shown by squares and females by circles.