Many different genes are involved in the production of pigments in mammals. One example is the TYR gene. In humans the TYR gene is located on chromosome 11. Fig. 6.1 shows the homologous pair for chromosome 11. Fig. 6.1 (i) Homologous chromosomes have the same genes located at the same loci. State one other feature shared by homologous chromosomes. ....................................................................................................................................... . ................................................................................................................................. (ii) Albinism in humans can be caused by recessive mutations of the TYR gene. Explain why a person who is homozygous recessive for the TYR gene shows albinism. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

Biology

IGCSE&ALevel

CAIE

Exam No：9700_s24_qp_41 Year：2024 Question No：6(a)

Answer:

Knowledge points:

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

Answer:

Knowledge points:

Solution:

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