If tall (T) is dominant over short (t), what is the probability of tall offspring from a cross Tt x tt?

• A. 0%
• B. 25%
• C. 75%
• D. 50%

Answer: (D)

Dominance and inheritance patterns tell us what to expect when crossing genotypes. Here, tall is T (dominant) and short is t (recessive). Crossing a heterozygous tall parent (Tt) with a homozygous short parent (tt) means the tall parent can pass either T or t, while the short parent can only pass t. So the possible offspring are Tt or tt, in a 1-to-1 ratio. Since Tt shows the tall phenotype and tt shows short, half of the offspring will be tall. The probability of a tall offspring is 50%.