Question 1

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 2

Interpret the following examples of chromosome karyotypes.
a) 47,XX,+mar.
b) 45,XY,der(13;14)(q10:q10) .
c) 46,XX,del(15)(q11q13).
d) 46,XY,t(3;17)(q26q23)

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a)...

Question 3

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

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Question 4

Which, if any, of the following statements is false?

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A)  Gain-of-function mutations are often missense mutations. 
B)  A missense mutation that has a dominant-negative effect can often produce a greater loss of protein function than a null mutation. 
C)  Pathogenic gain-of-function and loss-of-function mutations in the same gene produce different phenotypes . 
D)  A mutant protein that antagonizes the wild type protein produced from the normal allele is known as a hypomorph.

Question 5

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

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Question 6

Regarding chromosome nomenclature, explain the following terms:
a) distal
b) proximal
c) acentric chromosome
d) derivative chromosome

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a)...

Question 7

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

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Question 8

Fill in the blanks using numbers.
Depending on our ethnic background, each of us carries about ___1___or so mutations that would be expected to result in loss of gene function (with an average of ___2____ genes that are homozygously inactivated), plus about ____3____ missense variants that severely damage protein structure. When you factor in additional mutations in noncoding DNA, a normal person might be expected to have a total of over ____4____ damaging DNA variants.

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Depending on...

Question 9

Genetic variation can cause disease by causing a gene product to have an altered sequence of amino acids or ribonucleotides, or by altering the amount of gene product that is made. Describe the different ways in which genetic variation leads to a change in the amount of gene product.

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Question 10

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 11

What is a synonymous substitution and when does it not mean a silent mutation?

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Question 12

In terms of its contribution to pathogenesis which of the following mutant proteins is the odd one out, and why is it the exception?

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A)  $\beta$-globin carrying the p.Glu6Val substitution . 
B)  PI*Z and PI*E mutant $\alpha$1-antitrypsins 
C)  mutant CFTR protein with the common p.Phe508del deletion. 
D)  mutant prion proteins.

Question 13

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 14

Match the descriptions of a type of mutation given in
a) to
d) with one of the possible mutations listed in i) to iv).

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Question 15

Fill in the blanks using single words or with one or two letters.
The most commonly used method in human chromosome banding is known as ___1___-banding, when the chromosomes are treated with trypsin and then stained with the ____2____ dye. The ____2____ dye binds preferentially to ___3____-rich regions in DNA and the staining produces a series of alternating ____4____ bands that are ____2___-positive and ___3____-rich and ____5____ bands that are ____2___-negative and ___6____-rich. The ____4____ bands have a generally ____7____ content of genes, whereas the ____5____ bands have a ____8____ content of genes.

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Question 16

Regarding mutations, which of the following statements, if any, is false?

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A)  A de novo mutation is one that has occurred post-zygotically. 
B)  Each of us has multiple genes where both the maternal and paternal alleles have inactivating mutations. 
C)  The vast majority of mutations in our DNA do not adversely affect gene expression. 
D)  The mitochondrial genome has a very high gene density and accordingly the mutation frequency in mtDNA is low.

Question 17

Concerning disorders resulting from unstable expansion of tandem oligonucleotide repeats, which, if any of the following statements is false.

Accepted Answer

A)  The expansions can occur in coding DNA in some cases, and in noncoding DNA in other cases. 
B)  The repeats are of a variable number of nucleotides (from three to six) in both coding DNA and noncoding DNA. 
C)  The expansions in noncoding DNA are generally much larger in size than those in coding DNA. 
D)  The expanded arrays in noncoding DNA always result in loss of function of the host gene or of a neighboring gene.

Question 18

"The pathogenesis of sickle cell anemia is due to aberrant protein aggregation. Explain how.

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Question 19

Why should cysteine be the least mutable amino acid?

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Question 20

The genetic code that is used in our mitochondrial differs from the "universal" genetic code in the case of four codons. What are these codons and how does their interpretation differ between nuclear DNA and mitochondrial DNA?

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