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Genetic variation from meiosis and fertilisationAQA A-Level Biology: Flashcards

What these 13 flashcards ask

  • Give two sources of genetic variation in meiosis.
  • What is independent segregation?
  • What is crossing over?
  • Between which chromatids does crossing over occur?
  • When does crossing over happen?
  • What is random fertilisation?
  • How does random fertilisation increase variation?
  • Formula for chromosome combinations in a gamete without crossing over?
  • Formula for chromosome combinations in a zygote after random fertilisation, without crossing over?
  • How many gamete chromosome combinations for n = 5?
  • How many zygote combinations for n = 5?
  • What does n stand for in 2^n?
  • Why does crossing over add variation beyond independent segregation?

Exam questions on Genetic variation from meiosis and fertilisation

  1. A species of beetle has eight chromosomes in each body cell, arranged as four pairs of homologous chromosomes. Researchers are studying how many genetically different gametes one beetle can produce.
    Explain how independent segregation of homologous chromosomes produces genetic variation in gametes.2 marks
  2. Humans have 23 pairs of homologous chromosomes in their body cells. A student compares the possible variation in human gametes with that in the fruit fly, which has four pairs of homologous chromosomes.
    Calculate the number of different chromosome combinations possible in the gametes of a fruit fly, and in the zygotes formed by random fertilisation, ignoring crossing over.2 marks
  3. A plant is heterozygous for two genes that are on the same pair of homologous chromosomes. One chromosome of the pair carries alleles AA and BB and the other carries alleles aa and bb. The plant is allowed to undergo meiosis to make gametes.
    Describe how crossing over leads to new combinations of alleles on the chromatids of the plant.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).