Question

In a plant species, flower colour yellow is dominant over white, and fruit shape round is dominant over elongated. Crossing was performed between two pure one having yellow-flower and round fruit, and another with white flower and elongated-fruit. About 20 plants survived in F1 progeny. Plants of F1 were allowed to self-fertilize, and about 960 plants survived in F2. If the traits follow Mendelian inheritance, the number of plants would have yellow-flower and round-fruit in F1 and F2 are respectively
A.20, 960
B.20, 540
C.10, 180
D.10, 600

Answer 1

Hint: Here it is clearly said that yellow and round shape are the dominant qualities over white and elongated-fruit criteria. Progeny is the descendants. So, F1 is the first fertilization where 20 plants were survived as said in the question. As the cross happened further in F1 and self-fertilizing criteria was allowed, there are 960 plants as we receive in F2. Here it is asked the numbers of flowers and fruits showing the dominant trait in both progenies.

Complete answer:
1. As we know that the cross has happened between two pure varieties of yellow-flower and round-fruit (YYRR) and white flower and elongated fruit (yyrr). In F1 progeny, we call yellow flower and round fruit (depicting the dominant quality that is, YyRr).
2. For allowing self-fertilizing during F2, according to the Mendelian inheritance law, the phenotypic ratio would be “9 yellow-flower and round-fruit : 3 yellow-flower and elongated-fruit : 3 white flower and round fruit : 1 white flower and elongated fruit”.
3. You can see that 9 out of 16 progeny shows the quality of yellow flower and round fruit in F2 progeny. The total number of yellow flower and round fruit progeny in F2 will be \[\dfrac{9}{{16}} \times 960 = 540\]
4. So, we know already that in F1 progeny there are 20 plants. So, the correct option will be 20, 540, that is option B.
Hence, the correct answer is option (B)

Note: In order to find the phenotypic ratio, we need to know that a relative or changeable number of offspring manifest a particular trait or combination of two traits (as dominant) after crossing. For example, at the time of crossing between a tall and short plant, it would be noticed that some of the offspring will be tall and others will be short. Based on the genotype, the phenotypic ratio will depict the number of tall and short plants as offspring.