2015 GV question

In the 2015 GV paper Q3 c why is it important to mention how many homozygous recessive are produced when two heterozygous induvial mates. The homozygous recessive will die from the lethal alleles so they won’t be able to pass on alleles. Instead I mentioned that when two hetergoztoe mate they will produce 2 hetero offspring who continue to act as carriers of the lethal allele.

Mentioning the percentage of homozogous reccessive offspring produced seems to be an excellence point, but it doesn’t make sense to me.


I am uncertain how to answer your question?
2015 Q3c
This question has an “E” opportunity and has a strong focus on "why the cystic fibrosis lethal allele remains "

As with most “discussion” type questions in the Bio paper, there is a requirement to comprehensively cover as many aspects of the key ideas as possible, and where possible clearly link it to the resource given.

Heterozygotes are carriers of the alleles and they do not have symptoms of cystic fibrosis. Hence, phenotypically, it will be hard to distinguish who has it and who does not.
They key point here is that since heterozygotes are unaffected, if two heterozygotes mate and reproduce, there is a 25 % chance they will produce an offspring with the cystic fibrosis phenotype and 50% chance to produce an individual who is a carrier (another heterozygote)

Using the percentages support your understanding that heterozygotes live long enough to reproduce and pass on their alleles hence, hard the allele remains in the population.

Also bear in mind that the assessment schedule only shows you an expected coverage of what could be used as supporting evidence for the Excellence.
It could be that, for that year, that question was badly answered and many people did not use percentages in their answer to justify their response.

Hope that helps