Question

3. For what kind of sequence is the mutation rate and the neutral mutation rate likely to be identical? a) exons b) 3’-­UTRs c) introns d) pseudogenes e) 5’-­flanking regions

4. In a particular population an investigator measures DNA sequence variation for the X chromosome, the autosomes, the Y-chromosomes, and the mitochondrial genome. For sites free of natural selection and assuming the same mutation rate across chromosomes, what is the expected rank order of neutral heterozygosity these chromosomes? Why?

5. Would you expected similar levels or different levels of heterozygosity for Y-linked vs. mitochondrial DNA for sites free of selection? Explain.

6. Assume the neutral mutation rate varies across the genome of Drosophila melanogaster and also assume that the sister species D. simulans exhibits similar patterns of neutral mutation rate variation across homologous genomic regions. If one estimated across the genome, nucleotide heterozygosity in D. melanogaster and divergence to D. simulans, what would the correlation look like between nucleotide heterozygosity and nucleotide divergence (would it be zero, positive, or negative) and why?

7. At a particular gene an investigator observed 2 synonymous and 6 non-synonymous differences between two species. If a total of 40 polymorphisms were observed in sample of alleles for one of the species, what would the expected number of synonymous and non-synonymous polymorphisms in this species be under neutrality?

Answer 1

3)

• Neutral mutation is one in which mutation occurs in a sequence and this mutation doesnot cause any change in the protein produced.
• Mutation rate is increased in non coding sequences like introns and the mutation rate is higher .
• hence the answer is option c.

4)

• The order of the mutation rate is higher in mtDNA > Y chromosome > Autosomes > X chromosome
• Y chromosome is present only in males and therefore if the male is heterozygous it exhibits higher mutation rate.
• mtDNA mutation rate is dependent on Y chromosome.
• X chromosomes and autosomes are present in higher number about 3/4 of total chromosomes.
• X chromosome has lowest mutation rate compared to autosomes.

d)

• mtDNA mutation rate is dependent on Y chromosome .
• Hence the mutation rate will be similar to Y chromosome.