Question

Which of the following represents a test cross in which half the offspring is heterozygous and half would be homozygous recessive?

• A. TT × tt
• B. Tt × tt
• C. Tt × Tt
• D. tt × tt

Answer 1

The Correct Option is B

To determine which cross results in half the offspring being heterozygous (Tt) and half being homozygous recessive (tt), we need to analyze the options given:

• TT × tt: All offspring will be Tt (heterozygous), so this does not match the criteria.
• Tt × tt: Leads to the following combinations:
  • Tt (from Tt × tt)
  • tt (from Tt × tt)
• Tt × Tt: Results in Tt, Tt, TT, and tt, which means 25% TT, 50% Tt, and 25% tt; this does not satisfy the condition.
• tt × tt: All offspring will be tt (homozygous recessive), which does not match the criteria.

Therefore, the test cross that produces half heterozygous (Tt) and half homozygous recessive (tt) offspring is: Tt × tt

Answer 2

In a test cross, one of the parents is always homozygous recessive (tt), and the other parent can be either homozygous dominant (TT) or heterozygous (Tt).

• If the cross is Tt × tt, we can predict the offspring's genotypes using a Punnett square. The possible offspring genotypes will be:
• Tt (heterozygous) – 50% chance
• tt (homozygous recessive) – 50% chance

Thus, half of the offspring will be heterozygous (Tt) and the other half will be homozygous recessive (tt).