In pea plants, height is determined by an allele for tallness (T) that is dominant over an allele for shortness (t). What is the probability that a gamete, selected at random, would carry the short allele (t) in a cross of heterozygous tall pea plants?

Ans.

Heterozygous organisms show presence of two alternatives alleles for same trait. For plant height, a heterozygous tall plant, will show both the T (for tallness) and t (for shortness) alleles, as T allele is dominant over t allele. When a cross is made between heterozygous tall plants (Tt), there are 50% chances that a randomly selected allele will carry allele for shortness (t) as shown below:

Thus, "the probability that a randomly selected gamete will carry 't' allele in a cross between heterozygous tall pea plants, is 1/2."