Question

8. In an attempt to breed winter barley that is resistant to barley mild mosaic virus, agricultural researchers cross a susceptible domesticated strain with a resistant wild strain. The F1 plants are all susceptible, but when the F1 plants are crossed with each other, some of the F2 individuals are resistant. Is the resistance allele recessive or dominant? How do you know?

Answer 1

Answer:

The resistance allele is recessive

Explanation:

According to Darwin's pea experiment, the recessive trait appeared after a few generations.

Here in this case too the resistant individuals appeared after the first generation. This also implies that the offspring of first generation must be carrier of this recessive trait.

Let the susceptible domesticated strain  trait be represented by "S"

and the recessive resistant wild  strain trait be represented by "s"

Then,

F1 generation

SS * ss

Ss, Ss, Ss, Ss ------ All are heterozygous susceptible individuals

F2 generation

Ss * Ss

SS, Ss, Ss, ss

ss shows reappearance of resistant wild  trait.

Hence, the resistance allele is recessive.