Question 1

Two groups of human disorders involve expansion of tandem trinucleotide repeats in coding DNA to give gene products with abnormally long polyglutamine or polyalanine repeats. The pathogenic mechanisms have rather different characteristics, however in the way that the trinucleotide repeats expand. In what ways do they differ?

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Question 2

How does just a single loss-of-function allele cause a dominantly inherited disorder?

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Question 3

What are the characteristics of a Robertsonian translocation?

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Question 4

Match each of the genetic mechanisms
a) to
d) with one or more of the possible outcomes i) to iv).

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a) to
d)...

Question 5

A chromosome has received two double-stranded breaks. What kinds of chromosome abnormalities can result?

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Question 6

Why should cysteine be the least mutable amino acid?

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Question 7

Certain sequence classes in our genome are particularly prone to mutations. List three examples and explain why they are so prone to mutations.

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Question 8

How can a missense mutation with a dominant-negative effect result in greater loss of protein function and more severe disease than a full length gene deletion at the same gene locus?

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Question 9

List three examples of single gene disorders that show an extremely limited range of point mutations and explain why there should be such mutational homogeneity.

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Question 10

In the sequence below, the blue sequence represents an exon containing coding DNA near the beginning of a large gene and green lines and letters are flanking intron sequence. Nine mutations are shown: an insertion of an Alu repeat insertion plus three deletions at top and five single nucleotide substitutions below. Comment on the mutation class in each case and on its likely effect.

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Question 11

Amino acids can be divided into non-polar amino acids and polar amino acids. List the five different classes of polar amino acids.

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Question 12

Deletions, duplications and inversions in our DNA often result in interaction between tandem repeats, direct repeats, or inverted repeats. What are the essential differences between these repeat classes.

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Question 13

Give three examples of disorders where the pathogenesis can result from recurring large deletions and one where the pathogenesis can result from a recurring large duplication.

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Question 14

What is a cryptic splice site? What are expected consequences of activation of i) a cryptic splice donor site located within an exon ii) a cryptic splice acceptor site within an intron?

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Question 15

What is the major natural role of the nonsense-mediated decay mechanism in our cells?

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Question 16

What is meant by aneuploidy, and how does it occur?

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Question 17

The number of cell divisions needed to make human gametes differs extensively between men and women and also between different men. Explain these differences.

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Question 18

Give two examples of genes where loss-of-function and gain-of-function mutations result in different disease phenotypes.

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Question 19

Constitutional aneuploidy is occasionally viable in humans. Why should having fewer or extra copies of certain chromosomes be compatible with life, but not so in the case of other chromosomes?

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Question 20

Sequence exchange between two non-allelic copies of the same long sequence on chromosomal DNA molecules can have different consequences, depending on the positioning of the repeats that participate in sequence exchange. In (i) to (iii) imagine that there is sequence exchange between non-allelic sequence copies A and B shown by the blue arrows - the sequence exchange is between different chromatids of the same chromosome in the case of (ii). What types of sequence exchange might occur and what would be the likely outcome?

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Quiz 7: Genetic Variation Producing Diseasecausing Abnormalities in Dna and Chromosomes