Genetics

The ratio 1 red : 2 pink : 1 white is obtained due to incomplete dominance. In this case, the genotype is 1 RR : 2 Rr : 1 rr.

This is the correct answer. The explanation for it is as follows:
Parents : I^Ai x I^Bi
Gametes: I^A   i   x   I^B   i
Offsprings: I^AI^B,  I^Ai, I^Bi,  ii

AB blood group is formed when alleles I^A and I^B come together. Both alleles are equally dominant so they are equally expressed as AB group.

This is the correct answer. The cross is as follows:
Parents : I^Ai x I^Ai
Gametes: I^A   i   x   I^A   i
Offsprings: I^AI^A,  I^Ai, I^Ai,  ii

There is no possibility of getting white flowers. The only possibilities are red and pink.
The cross is depicted as follows:
Parents: Pink x Red
Genotype: Rr x RR
Gametes: R, r x R, R
Offsprings: RR and Rr
(ie. Red and pink)

The cross is depicted as follows:
Parents: TtYY x ttyy
Gametes: TY, tY x ty
Offsprings: TtYy and ttYy
(ie. Tall yellow and dwarf yellow)

One gene having more than one effect is called pleiotropy.

The change of glutamic acid to valine in the sixth position of beta globin chain of haemoglobin causes sickle cell anaemia.

Different forms of the same gene are called alleles, e.g., T and t are alleles for stem height.

Since blood groups in humans are controlled by 3 alleles, i.e., I^A, I^B and i, it is an example of multiple allelism.

Pleiotropy is an instance where one gene has more than one effect. In this case, amount of starch grain produced as well as seed shape are the two effects.

This is the correct answer. The cross can be depicted as follows:
Parents : AB x O
Genotype: I^A, I^B x ii
Gametes: I^A, I^B x i
Offsprings: I^Ai and  I^Bi

Here, both genotypic and phenotypic ratios are the same, i.e., genotypic ratio is 1 RR:2Rr:1rr and phenotypic ratio is 1 red:2 pink:1 white.

Down's syndrome is an example of trisomy in chromosome 21.

In this case, a child produces a characteristic mewing cry like a cat and exhibits severe physical and mental retardation. So, it is called Cri-du-chat syndrome.