IB Biology HL D4.1 Natural selection questions

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Type
Multiple choiceWritten
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Question 1

Multiple choiceEasy1 mark

The offspring of a cross between two plants carry combinations of alleles at two genes that were not together in either parent, although every allele was present in at least one parent. What process explains this variation?

Show answer and explanation

Answer: B. Sexual reproduction combines alleles from the parents, creating new combinations of alleles already present. The alleles themselves need not be new for offspring to show a new combination.

A: confuses a new combination of alleles with a new allele, which mutation can produce.
C: treats a change in allele frequency through natural selection as the source of the offspring’s combination.
D: selects transmission from one parent, rather than the combination of alleles from two parents.

Remember: mutation generates new alleles; sexual reproduction generates new combinations of alleles.

Question 2

Paper 2Medium16 marks

In a moth population, wing pattern is controlled by two alleles, B and b. The B allele gives dark wings and is dominant; moths with genotype bb have pale wings. Treat the counts below as the complete populations, so ignore sampling error.

GenerationPopulation information
11000 moths; 160 have pale wings
21000 moths; 400 BB, 400 Bb and 200 bb

Assume generation 1 is in genetic equilibrium. Allele counting in generation 2 gives p = 0.60 and q = 0.40. Records of the mating pairs that produced generation 2 show that moths preferentially mated with partners having the same wing pattern.

(a)

State what p and q represent for this gene and give their relationship.

[2]
(b)

Calculate p and q for generation 1, and the expected frequencies of BB, Bb and bb.

[5]
(c)

Calculate the observed genotype frequencies in generation 2. Determine whether they fit the Hardy–Weinberg equation for the allele frequencies given.

[4]
(d)

Explain how the mating pattern could account for the genotype frequencies in generation 2.

[2]
(e)

State three conditions, other than random mating, required for a population to remain in genetic equilibrium.

[3]

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