Reason for trisomy in Down's syndrome is:

Mental retardation in man occurs due to:

Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R) Assertion (A): A father will never pass the gene for haemophilia to his sons. Reason (R): Haemophilia is sex-linked (X-linked recessive trait). In the light of the above statements, choose the correct answer from the options given below:

A certain plant homozygous for yellow seeds and red flowers was crossed with a plant homozygous for green seeds and white flowers. The F1 plants had yellow seeds and pink flowers. The F1 plants were selfed to get F2 progeny. Assuming independent assortment of the two characters, how many phenotypic categories are expected for these characters in the F2 generation?

In Drosophila the XXY condition leads to femaleness whereas in human beings the same condition leads to Klinefelter's syndrome in males. It proves:

What ratio is expected in offsprings if father is colour blind and mother's father was colour blind:

In a cross between a male and female, both heterozygous for sickle cell anaemia gene, what percentage of the progeny will be diseased?

Among fraternal twins, one baby is haemophilic while the baby's brother is normal. Which statement is true?

A genetic map is one that: