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5 marksPatterns of Inheritance

CAPE Biology Unit 1 · 2009 · Paper 2 · Question 2(a)(ii)

Hair colour in mice is controlled by two genes. Gene 1: dominant allele B for black hair, homozygous recessive bb for brown hair. Gene 2: dominant allele A for pigment deposition (black or brown), homozygous recessive aa for white (albino) regardless of the first gene's genotype.

Crosses between black mice, all heterozygous for both genes, produced offspring with black, brown and white coat colour. Determine the ratio of the phenotypes and for EACH phenotype suggest ONE genotype.

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Other parts of this question

  1. 2(a)(i)State the term used to describe the interaction of the two genes described above, and give an explanation of the nature of the interaction.[3 marks]
  2. 2(b)(i)Identify the stages labelled as X, Y and Z.[3 marks]
  3. 2(b)(ii)State TWO features of the stage in Meiosis I which comes after Stage Z.[2 marks]
  4. 2(b)(iii)Explain how the events shown in Stage X of Meiosis I contribute to heritable variation.[2 marks]

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