Answer 5 of the 8 questions
(The answers may be obtained here.)
Time allowed 1 hr. 15 min.
All questions are of equal value
1. a) What features of meiosis account for the second law (of independent assortment of genes) deduced by Mendel?
b) Manx cats are tailless. When a tailless Manx cat mates with a normal tailed cat half the kittens are tailless and half have normal tails. When two Manx cats mate two thirds of the kittens are tailless and one third have normal tails. What simple explanation might account for this deviation from the results which you might have predicted from Mendel's first law?
2. a) Explain the meanings of the following terms which can sometimes complicate the interpretation of pedigrees: genetic heterogeneity, epistasis, variable expressivity.
b) In the following family there is a genetic disease present which is usually thought to be caused by an X linked recessive mutation. Is the pattern of inheritance entirely consistent with that mode of inheritance? What other explanations might be worth consideration?
3. A number of Mendelian traits were examined in the pedigree below. What is the most likely mode of inheritance of each?
4. a) What evidence from patients with abnormal karyotypes suggested that there is a sex determining gene on the human Y chromosome? What is this gene? Give two pieces of evidence which proved its role.
b) Why are abnormal numbers of sex chromosomes less damaging to human development than are abnormal numbers of autosomes?
5. a) Explain what is meant by the term frameshift mutation.
b) What may be the consequences of a splice site mutation
c) Give two examples of recurrent mutations caused by duplicated DNA sequences.
6. a) Explain the meanings of the following terms in cytogenetics:
i) aneuploid ii) centromere iii) Robertsonian translocation iv) metacentric
b) What may be the consequences of heterozygosity for a paracentric inversion
7. In the family shown below two baby boys have been born who are now showing the symptoms of muscular dystrophy. Doctors suspect that the symptoms do not match those of Duchenne Muscular dystrophy (which is located at Xp21) and they hypothesise that an autosomal mutation might be responsible for the disease in this family. Two multi-allelic X linked genetic markers, DXS123 and DXS246, on the short arm of the X chromosome were typed in the family. The results are shown below. Do these results tend to confirm or deny this hypothesis?
What experiments or other research would you suggest next?
8. a) Explain why the genetic disease porphyria variegata is present at a much higher frequency in the South African Boer population than it is in the Dutch population from which the Boers are descended.
b) What is the relevance of population genetics to forensic DNA fingerprinting?
END OF PAPER