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Monohybrid inheritance and sex linkageEdexcel International A Level Biology: Flashcards

What these 13 flashcards ask

  • Define 'allele'.
  • What is the difference between genotype and phenotype?
  • What is a recessive allele?
  • What is the difference between a homozygote and a heterozygote?
  • What is codominance?
  • What is the genotype ratio of Ff × Ff?
  • Two carriers have a child. What is the probability that it is affected?
  • What is a carrier?
  • What does a pedigree with two unaffected parents and an affected child show?
  • Why is red-green colour blindness more common in males?
  • Can a colour-blind father pass colour blindness to his son?
  • Give the genotypes of a woman who is a carrier of red-green colour blindness.
  • A carrier woman has children with a man of normal vision. What fraction of their sons are colour blind?

Exam questions on Monohybrid inheritance and sex linkage

  1. Cystic fibrosis is caused by a recessive allele, f, of a single gene on an autosome. The dominant allele is F. Two parents who do not have cystic fibrosis are expecting a child, and the couple already have one child who has cystic fibrosis.
    Explain how two parents who do not have cystic fibrosis can have a child who has the condition.2 marks
  2. In a breed of cattle, coat colour is controlled by one gene with two alleles, CRC^{R} (red hairs) and CWC^{W} (white hairs). Neither allele is dominant. Cattle with the genotype CRCWC^{R}C^{W} have a roan coat, with both red and white hairs.
    A roan bull is crossed with a white cow. Give the genotypes of the possible calves and the expected ratio of their phenotypes.2 marks
  3. A rare inherited condition is studied in a family. Neither individual 1 (a man) nor individual 2 (a woman) has the condition. They have three children: individual 3, a daughter who has the condition, and individuals 4 and 5, two sons who do not have the condition.
    Deduce the mode of inheritance of this condition, using evidence from the family.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).