If a boy's father has haemophilia and his mother has one gene for haemophilia, what is the chance that the boy will inherit the disease?

• 100%

• 50%

• 0%

• 75%

Pureline breed refers to

• homozygosity

• heterozygosity

• homozygosity with only dominant genes

• heterozygosity and linkage

Barr-body in mammals represents

• one of the two X-chromosomes in the cells

• all heterochromatin of male and female cells

• Y-chromosome of male

• all heterochromatin of female cells

Discontinuous variations are

• essential features

• acquired character

• non-essential changes

• heritable changes

The linkage map of X-chromosome of fruit-fly has 66 units, with yellow body gene (y) at one end and bobbed hair (b) gene at the other end. The recombination frequency between these two genes (y and b) should be

• $\le$50%

• 100%

• 66%

• > 50%

In Drosophila, the sex is determined by

• the ratio of pairs of X-chromosomes to the pairs of autosomes

• whether the egg is fertilised or develops parthenogenetically

• the ratio of number of X- chromosomes to the set of autosomes

• X and Y-chromosomes

Down's syndrome is caused by an extra copy of chromosome number 21. What percentage of a normal father would be affected by this disorder?

• 50%

• 25%

• 100%

• 75%

Genetic map is one that

• shows the stages during the cell division

• shows the distribution of various species in a region

• establishes sites of the genes on a chromosome

• establishes the various stages in gene evolution

Mirabilis jalapa shows

• codominance

• incomplete dominance

• dominance

• complementary genes

380.

Which of the following is not related to sex chromosome X or Y?

• Turner's syndrome

• Klinefelter's syndrome

• Down's syndrome

• Haemophilia and colour bindness