A recent estimate of the rate of base substitutions at SNP loci is about 1x10-8

Question

A recent estimate of the rate of base substitutions at SNP loci is about 1x10-8 per nucleotide pair pergamete.

a. Based on this estimate, about how many de novo mutations (that is, mutations not found in the

genomes of your parents) are present in your own genome?

b. Where and when did these de novo mutations in your genome most likely occur?

c. It has been calculated that each sperm made in a 25-year-old man is the result on average of about 300rounds of cell division, starting with the first mitotic division of the male zygote. In contrast, eachmature oocyte found in a 5-month-old female human fetus is the result of about 25 rounds of division,starting with the first mitotic division of the female zygote. What bearing do these calculations have onthe estimate of the rate of base substitutions in humans, and on your answer to part b

Explanation / Answer

a. 6 billion base pairs are present in double stranded DNA. This means that there are six billion positions where a SNP can ocuur.

Number of base substitutions at one point = 1*10^-8

Number of base substitutions at 6 billion positions = 1*10^-8 * 6 * 10^9 = 60 mutations

Genome is the haploid set of genes of an individual. So, 60/2 =30 de novo mutations can be found in one genome.

b. Most commonly SNPs occur in DNA present between genes. They act as biomarkers. These occur at the time of DNA replication.

c. Mostly SNPs occur in DNA between genes and act as biological markers. They help scientists to trace the location of defected genes. This is general. These are the reason of most of variations in humans.

If a SNP occurs in the gene or in the regulatory region, then it may have a beneficial or deleterious effect.

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