AP BIOLOGY

Detailed explanation-1: -Each parental generation can produce only one type of gamete, YR or yr. F1 generation: The F1 dihybrid seeds are yellow and round, with a genotype of YyRr. The F1 plants can produce four different types of gametes: YR, Yr, yR, and yr.

Detailed explanation-2: -The gametes formed are YR and yr. After fertilisation, the F1 heterozygote will be formed i.e YyRr (yellow and round). On selfing F1 we get two possible combinations i.e YR, Yr, yR, yr. Therefore four types of gametes are formed in the ratio of 1:1:1:1.

Detailed explanation-3: -When the plant with Yyrr genotype is crossed with a plant with YYRR genotype, it produces three types of gametes, YR, Yr and yr.

Detailed explanation-4: -Thus, there are four equally likely gametes that can be formed when the YyRr heterozygote is self-crossed as follows: YR, Yr, yR, and yr.

Detailed explanation-5: -From the cross worked out in the above Punnett square, we can see that the gametes from both parents combine to give rise to progeny with two characteristic genotypes, YyRR and yyRR. The chance for occurrence of each of these genotypes is 50%.