Genetics: Why Calico Cats Are Almost Always Female
A tour of genetics, from Mendel's peas to epigenetics, through the ideas that most surprise people.
Genetics · 50 questions
Try 3 questions
1. Two pea plants, both Aa, are crossed. Among offspring showing the dominant trait, what fraction are heterozygous?
- One out of two
- One out of four
- Two out of three
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Answer: Two out of three
Dominant-looking offspring are AA, Aa and Aa in a 1:2 ratio, so two of every three carry the hidden recessive allele.
2. A plant has genotype Aa. What fraction of its pollen grains carry the a allele?
- A quarter of them
- All of them
- Half of them
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Answer: Half of them
Mendel's law of segregation: the two alleles separate during meiosis, so each gamete gets one, and half receive a.
3. To learn whether a plant showing a dominant trait is AA or Aa, what should you cross it with?
- A homozygous recessive plant
- A homozygous dominant plant
- Another heterozygous plant
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Answer: A homozygous recessive plant
In this test cross, any recessive-looking offspring reveal that the tested plant carried a hidden recessive allele.
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