Biology Inheritance / Variation & Genetics UHS 2023
PMDC Verified Question 32 of 94
Test cross is made to check the genotype of a trait. Which of the following crosses is a test cross?
A
Unknown × Tt
B
Unknown × tt
C
Unknown × AB
D
Unknown × TT
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Unknown × tt
Concept:

An organism displaying a dominant phenotype could be either homozygous dominant or heterozygous. A test cross reveals this hidden genotype.

Solution:

  • A test cross involves crossing an individual with an unknown genotype (showing the dominant trait) with a completely homozygous recessive individual.
  • If the unknown is TT, all offspring will show the dominant trait.
  • If the unknown is Tt, 50% of the offspring will show the recessive trait.
  • Therefore, crossing the unknown with tt is the correct format for a test cross.


Why other options are incorrect:

  • Crossing with a dominant genotype (TT or Tt) would result in all offspring showing the dominant trait, masking any recessive alleles the unknown parent might be carrying.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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