(4) A couple, both of whom are heterozygous carriers of a recessive disease alle

Question

(4) A couple, both of whom are heterozygous carriers of a recessive disease allele, have two children. What is the probability that both children are affected with the disease? [2 points] You repeat one of Mendel's experiments to examine stem length in peas, where long stems are dominant to short stems. You cross a true-breeding long-stem plant with a true-breeding short- stem plant, self the resulting F1 plants, and generate 576 F2 plants. How many of the F2 plants do you predict will exhibit long stems? (5) 12 points)

Explanation / Answer

4. If parents ate heterozygous carriers, then there is 25% chance in each pregnancy of child affected with disease. As there are two children, the probability is 1/2.

5. According to Mendel theory, dominant to recessive ratio in F2 generation is 3:1, so 432 plants will have long stems.

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