QUESTION 98 (8 marks)
Before a wildlife corridor opens, researchers mark 54 frogs in an isolated wetland. A second capture contains 75 frogs, 18 marked. Assume Lincoln-index conditions are met. A separate representative genetic sample estimates A frequency as 0.20 at one diploid locus. After the capture study finishes, the corridor allows 15 AA frogs to join the breeding population; no other population changes occur.
a) Estimate the population before the corridor opens. [2 marks]
b) Use this estimate to calculate the number of A copies before immigration and the estimated A frequency after immigration. [3 marks]
c) Explain how the corridor could reduce the tendency for the wetland and source populations to diverge genetically. [2 marks]
d) Explain why these numerical results should be treated as estimates rather than an exact census. [1 marks]
Practice marking scheme
Answer
a) 225 frogs. b) 90 A copies initially; frequency becomes 0.25. c) Gene flow exchanges alleles and can oppose divergence through drift or different selection. d) Population and allele frequencies are inferred from samples.
Working
. The estimated original allele total is 450, of which are A. The immigrants add 30 A copies, giving . Breeding movement connects gene pools and can reduce differences that would otherwise accumulate in isolated populations. The Lincoln estimate and sample allele frequency both have sampling uncertainty and rely on assumptions.
Marking criteria
- Uses the Lincoln formula with the correct capture values. [1 mark]
- Calculates N = 225. [1 mark]
- Estimates 90 original A copies. [1 mark]
- Adds 30 A copies and uses 480 final alleles. [1 mark]
- Calculates final frequency 0.25. [1 mark]
- Links breeding movement to gene flow. [1 mark]
- Explains that exchange can oppose divergence/drift in isolated gene pools. [1 mark]
- Recognises sampling uncertainty and/or model assumptions. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.