In pea plants, the allele for tallness (T) is dominant to the allele for shortness (t). In the cross between a tall pea plant and a short pea plant shown below, what is the probability that the resulting offspring will be tall?

Question

T t
t ? ?
t ? ?
A.
25%
B.
50%
C.
75%
D.
100%

Answer 1

To determine the probability that the offspring will be tall from a cross between a tall pea plant and a short pea plant, we need to identify the genotypes of the parent plants.

• The tall pea plant could be either homozygous dominant (TT) or heterozygous (Tt).
• The short pea plant must be homozygous recessive (tt) because shortness is caused by the recessive allele.

For this example, let's assume the tall plant is heterozygous (Tt). The cross would look like this:

           T      t
         ----------------
     t |    Tt    |   tt  |
         ----------------
     t |    Tt    |   tt  |

From the Punnett square, we can see the following offspring genotypes:

• 2 Tt (tall)
• 2 tt (short)

This shows that 2 out of 4 offspring will be tall.

Calculating the probability:

• Probability of tall offspring = Number of tall offspring / Total offspring = 2/4 = 50%

Thus, the correct answer is B. 50%.