Assessment task: Extended response
(40 marks)
This task is in two parts. Part A requires you to consider gene frequencies in two populations.
Part B involves researching a genetic condition and answering questions relating to it.
Part A: Gene frequencies
(30 marks)
The ABO blood typing system is governed by genes IA and IB, which are codominant to the (i)
gene. The genotypes that exist are:
IA IA or IA i – type A
IB IB or IBi – type B
IA IB – type AB
ii – type O
The diagram below shows an original population – a hypothetical population of Aboriginals
and their blood group genotypes as they may have existed before they migrated to the
Australian continent. A number of individuals from this original group migrate to Australia,
resulting in an island population.
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1. Record the following in the tables provided:
(22 marks: 0.5 for each)
a) Count the number of alleles in both populations.
b) Count the number of allele combinations in both populations.
c) Calculate the allele frequencies as percentages for both.
Mainland population
Number
counted
%
IA
Allele types
IB
i
Allele combinations
I AI A
I Ai
I BI B
I Bi
I AI B
ii
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Mainland phenotype frequencies
Type A
Type B
Type AB
Island population
Number
counted
Type O
%
IA
Allele types
IB
i
Allele combinations
I AI A
I Ai
I BI B
I Bi
I AI B
ii
Island phenotype frequencies
Type A
Type B
Type AB
Type O
Use the following formula to calculate a gene (allele) frequency:
Gene (allele) frequency = number of specific alleles ÷ total number of alleles x 100
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2. Answer the following questions.
(8 marks)
a)
Describe how the allele frequencies of the two populations differ.
(2 marks)
b)
Predict what will happen to the allele frequencies for both populations after many
generations.
(2 marks)
c)
This type of colonisation of the island can be identified by which term?
d)
What other process could further alter the allele frequencies of the island population?
Why?
(2 marks)
e)
From the information given, name an evolutionary process that doesn’t appear to be
influencing the allele frequencies of both populations.
(1 mark)
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(1 mark)
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Part B: Genetic diseases
(10 marks)
The incidence of genetic diseases in populations can be related to some of the evolutionary
mechanisms discussed in this topic.
Choose one such disease from the list and then complete the questions.
List
Tay-Sachs disease
Down syndrome
haemophilia
cystic fibrosis
Klinefelter syndrome
1. In one paragraph describe the condition’s symptoms and any available treatment or
management strategy.
2. Try to find out where the condition originated from.
3. Why do you think the condition still persists in the population?
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