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Inheritance and phenotype

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Which term describes Aa at one locus?

  1. A gamete containing both homologues.
  2. Heterozygous.
  3. Homozygous.
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Heterozygous.

A and a are different alleles at the locus.

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Which observation best supports incomplete dominance?

  1. The dominant allele is the most common allele.
  2. The heterozygote has a uniform intermediate phenotype.
  3. The heterozygote visibly expresses both distinct parental effects.
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The heterozygote has a uniform intermediate phenotype.

It is intermediate between the two homozygotes.

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What is P(aabb) in the stated AaBb x AaBb independent cross?

  1. 1/16.
  2. 1/4, because every recessive phenotype has the same probability.
  3. 9/16.
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1/16.

P(aa) x P(bb) = 1/4 x 1/4.

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AaBb x AaBb, with independent assortment and complete dominance, gives 320 offspring. About how many show both recessive phenotypes?

  1. 20
  2. 180
  3. 80
  4. 60
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20

P(aabb) = 1/4 x 1/4 = 1/16, and 320 / 16 = 20.

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In the stated model, P(pink and tall) is:

  1. 3/8.
  2. 1/16.
  3. 9/16.
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3/8.

1/2 for pink x 3/4 for tall = 3/8.

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Which is a possible gamete from IAiMm?

  1. IAi.
  2. IAMm.
  3. IAm.
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IAm.

It contains one ABO allele and one marker allele.

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For the stated XNXnPp x XNYpp model, P(affected son with pp) among all offspring is:

  1. 1/8.
  2. 1/2.
  3. 1/4.
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1/8.

1/4 affected sons among all offspring x 1/2 pp.

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Which tester is appropriate for an unknown A_B_ individual?

  1. AABB, homozygous dominant at both loci.
  2. AaBb, heterozygous at both loci.
  3. aabb.
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aabb.

It supplies only recessive alleles at both loci.

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Two unaffected parents have an affected daughter. Assuming no new mutation, which conclusion does this family support?

  1. The allele is autosomal recessive, and both parents are carriers.
  2. The allele is X-linked recessive, because the condition skipped a generation.
  3. The allele is dominant, because the daughter shows the condition.
  4. Both parents must be homozygous dominant.
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The allele is autosomal recessive, and both parents are carriers.

Unaffected parents with an affected child show a recessive allele, and an affected daughter of an unaffected father rules out X-linkage.

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Which observation in a pedigree does NOT fit X-linked recessive inheritance?

  1. More males than females are affected
  2. An affected son has unaffected parents
  3. Daughters of an affected father are carriers or affected
  4. An affected father has an affected son
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An affected father has an affected son

A son receives his father's Y, not his X, so he cannot inherit an X-linked allele from his father.

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Which conclusion best fits queen-worker differentiation?

  1. Queens arise from fertilised eggs, whereas workers arise from unfertilised eggs.
  2. Queen development requires the larva to acquire a new DNA sequence for every queen trait.
  3. Different larval nutrition can alter developmental outcomes and gene expression.
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Different larval nutrition can alter developmental outcomes and gene expression.

This is the required environmental example.

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Question 1 of 12

Correct the gamete claim

3 marks

A student says an AaBb parent produces Aa and Bb gametes and that the common allele must be dominant. Correct both statements. [3]

Use locus, segregation and dominance precisely.

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