Cystic fibrosis is an autosomal recessive genetic disease. People with cystic fibrosis have a homozygous recessive genotype. A screening programme for cystic fibrosis was introduced in 2007 for all children born in the UK. Children are tested within seven days of their birth. Children identified from the screening programme as being at high risk of having cystic fibrosis can have a genetic test to confirm whether they have the disease. (i) Table 3.1 shows the median predicted life expectancy for people born in the UK who have cystic fibrosis. Predictions are shown for people born in 2008, 2012, 2016 and 2020. Describe the trend shown in Table 3.1 and outline how early screening for cystic fibrosis may have contributed to this trend. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ................................................................................................................................. (ii) In many countries, a genetic test for cystic fibrosis is available to adults who do not have cystic fibrosis but have a family member who either has cystic fibrosis or is heterozygous for the gene that causes cystic fibrosis. These adults include partners, parents, offspring, brothers and sisters of the family member. The aim is to find out if any of these adults are heterozygous for the gene that cause cystic fibrosis. Discuss the ethical and social considerations of making a genetic test for cystic fibrosis available to these adults. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................
Exam No：9700_m24_qp_42 Year：2024 Question No：3(c)
Answer:
Knowledge points:
16.1.1 explain the meanings of the terms haploid (n) and diploid (2n)
16.1.2 explain what is meant by homologous pairs of chromosomes
16.1.3 explain the need for a reduction division during meiosis in the production of gametes
16.1.4 describe the behaviour of chromosomes in plant and animal cells during meiosis and the associated behaviour of the nuclear envelope, the cell surface membrane and the spindle (names of the main stages of meiosis, but not the sub-divisions of prophase I, are expected: prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II and telophase II)
16.1.5 interpret photomicrographs and diagrams of cells in different stages of meiosis and identify the main stages of meiosis
16.1.6 explain that crossing over and random orientation (independent assortment) of pairs of homologous chromosomes and sister chromatids during meiosis produces genetically different gametes
16.1.7 explain that the random fusion of gametes at fertilisation produces genetically different individuals
16.2.1 explain the terms gene, locus, allele, dominant, recessive, codominant, linkage, test cross, F1, F2, phenotype, genotype, homozygous and heterozygous
16.2.2 interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of monohybrid crosses and dihybrid crosses that involve dominance, codominance, multiple alleles and sex linkage
16.2.3 interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of dihybrid crosses that involve autosomal linkage and epistasis (knowledge of the expected ratios for different types of epistasis is not expected)
16.2.4 interpret and construct genetic diagrams, including Punnett squares, to explain and predict the results of test crosses
16.2.5 use the chi-squared test to test the significance of differences between observed and expected results (the formula for the chi-squared test will be provided, as shown in the Mathematical requirements)
16.2.6.1 TYR gene, tyrosinase and albinism
16.2.6.2 HBB gene, haemoglobin and sickle cell anaemia
16.2.6.3 F8 gene, factor VIII and haemophilia
16.2.6.4 HTT gene, huntingtin and Huntington’s disease
16.2.7 explain the role of gibberellin in stem elongation including the role of the dominant allele, Le, that codes for a functional enzyme in the gibberellin synthesis pathway, and the recessive allele, le, that codes for a non-functional enzyme
Solution:
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