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Download 6.3 Chromosomes structure — Further questions Q1. Bk Ch6 S6.3
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6.3 Chromosomes structure — Further questions Q1. Bk Ch6 S6.3 FQ1 If a heterozygous blood group A person has children with a heterozygous blood group B, what genotypes may be shown by the offspring? Use a diagram to illustrate your answer. A1. Bk Ch6 S6.3 FA1 Alleles A and B are codominant, with allele O being recessive. A Punnett square can be used to illustrate the genotypes expected when parents with blood types A and B have children. B O A AB AO O BO OO Children of these parents could have any of the following blood groups: AB, A, B or O. Q2. Bk Ch6 S6.3 FQ3 The pedigree below shows the inheritance of a type of rickets that is resistant to vitamin D therapy. The disease is a sex-linked, recessive trait. a b Assign genotypes to the original parents. What is the genotype of the twin who married? Is it possible that she will have a son who is not affected or a daughter who is affected? Explain. A2. Bk Ch6 S6.3 FA2 N: normal; n: therapy-resistant rickets. a Father: XnY; mother: XNXn. b XnXn. No. An unaffected son will have the genotype XNY—this mother does not have a dominant allele to pass on to her sons. An affected daughter will have the genotype XnXn but in this case, although she will pass on the recessive allele to all of her daughters, the father is normal and therefore only has a dominant allele on his only X chromosome to pass on to his daughters. Q3. Bk Ch6 S6.3 FQ3 Find out what is meant by Y-linked inheritance. Describe the inheritance patterns for Y-linked inheritance, using specific examples. Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) A3. Bk Ch6 S6.3 FA3 Y-linked inheritance refers to the inheritance of genes carried on the Y chromosome. The Y chromosome carries fewer genes than the X chromosome and most of these genes are involved in the determination of sex and fertility in males. However, there are some other characteristics determined by genes carried on the Y chromosome. For example, the presence or absence of excessively hairy ears is a characteristic only passed from father to son and is therefore Y-linked. If a man has the gene for hairy ears then he will pass this characteristic on to all of his sons since all of his sons receive the Y chromosome from their father. Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd)