A true-breeding strain of tall soybean plants is crossed with a true-breeding strain of short soybean plants. All the offspring
are short. These offspring are then crossed with each other to create an F2 generation. If the height of soybean plants is due to a single gene, then of 200 F2 plants, _______ should be tall.
A typical monohybrid cross gives 3 dominant: 1 recessive progeny in the F2 generation. According to the given information, the allele for short height is dominant since it is expressed in the F1 generation obtained by crossing two pure breeding tall and short soybean plants.
A cross between two heterozygous short soybean plants would obtain F2 generation in the following phenotype ratio=
3 short (dominant): 1 tall (recessive).
The proportion of tall plants in F2 generation is =1/4
Therefore, the number of tall plants in F2 generation = 1/4 x 200 = 50
