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5.1 Inheritance

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Question 32

Genetic mapping can be used to determine the relative distance between two linked gene loci on a chromosome in eukaryotic organisms such as Drosophila melanogaster.

The statements below describe four stages of a two-point test cross experiment used to map linked genes, in random order:

  • I: A heterozygous F1 F_1\,F1​ dihybrid is mated with a double homozygous recessive tester individual.
  • II: The percentage of recombinant offspring is calculated to determine the genetic distance in map units (centimorgans).
  • III: True-breeding parental lines with homozygous dominant and homozygous recessive genotypes are crossed to produce a uniform F1 F_1\,F1​ generation.
  • IV: The resulting offspring are phenotyped and counted to classify them into parental and recombinant groups.

What is the correct chronological order of these stages?

A

I, III, IV, II

B

III, I, IV, II

C

III, IV, I, II

D

I, IV, III, II

Markscheme

5.1 Inheritance Questions

  1. GCSE
  2. /Biology
  3. /5.1 Inheritance

97 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.

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