Question

In a monohybrid cross, if the gene for tall (T) plants was incompletely dominant over the gene for short (t) plants, what would be the predicted result of crossing two intermediate (Tt) parent plants?
(Hint: You may want to complete a Punnett square)

A.) 25 percent tall, 50 percent intermediate, 25 percent short
B.) 50 percent tall, 25 percent intermediate, 25 percent short
C.) 100 percent intermediate
D.) 25 percent tall, 75 percent intermediate

Answer 1

Answer: alternative A.

Explanation: A crossing between two individuals with Tt phenotypes would result in the following offspring.

      / T  /  t  /

T/  TT   /  Tt

t/   Tt  /  tt

This offspring shows 3 different phenotypes: TT (tall plants, 25% of the result), Tt (a mix between tall and short plants, due to the incomplete dominance, 50% of the result) and tt (short plants, 25% of the result).

Answer 2

The result of the cross of an intermediate plant (Tt) with a tall plant (TT), when the tall gene (T) is incompletely dominant over the short gene (t) will be as shown in the punnet square below. The gametes formed will be T , T , T, and t (Where T is the allele for tall while t is the allele for short).The punnet square shows that the 50 % of the progeny of this cross will be tall (TT), and the other 50% will be intermediate (Tt). Hence, the correct answer is 'Option C - 50 percent tall, 50 percent intermediate'.