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Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene - HSC - SSCE Biology - Question 10 - 2021 - Paper 1
Question 10
Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene. Many different recessive alleles cause cystic fibrosis. The four most commo... show full transcript
Worked Solution & Example Answer:Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene - HSC - SSCE Biology - Question 10 - 2021 - Paper 1
Step 1
Identify the alleles and frequencies
Answer
In the provided information, the alleles of the CFTR gene and their respective frequencies in the Australian population are specified. The most common allele is 'A' with a frequency of 98.33%, followed by 'a1' (1.13%), 'a2' (0.08%), and 'a3' (0.07%).
Step 2
Determine the genotype for cystic fibrosis
Answer
Since cystic fibrosis is an autosomal recessive disorder, a patient must have two copies of the recessive allele to express the disease phenotype. The only genotype contributing to cystic fibrosis would be composed entirely of the recessive alleles 'a1', 'a2', or 'a3'. However, given the allele frequencies, we need to consider the common genotype in the population which includes the most frequent allele, 'A'.
Step 3
Calculate the most common genotype
Answer
The most common genotype among cystic fibrosis patients in Australia will primarily involve the dominant allele 'A'. The expected genotype will therefore be 'AA' for the majority of the population, as this genotype is associated with the absence of cystic fibrosis. Thus, heterozygous genotypes 'Aa1', 'Aa2', or 'Aa3' will also exist but are significantly rarer.
Step 4
Conclusion
Answer
In summary, the most common genotype of cystic fibrosis patients in Australia is 'AA', implying those not affected by the disease, due to the high frequency of the dominant 'A' allele. The presence of homozygous recessive genotypes like 'a1a1', 'a2a2', or 'a3a3' are exceedingly rare due to their low frequencies.