Question

You have constructed four different libraries: a genomic library made from DNA isolated from human brain tissue, a genomic library made from DNA isolated from human muscle tissue, a human brain cDNA library, and a human muscle cDNA library.

You wish to clone the human gene encoding myostatin, which is expressed only in muscle cells.

A. Assuming the human genome is 3×10^9 bp and that the average insert size in the genomic libraries is 100 kb, how frequently will a clone representing myostatin be found in the genomic library made from muscle?

Express your answer as a probability.

B. How frequently will a clone representing myostatin be found in the genomic library made from brain?

Express your answer as a probability.

C. How frequently will a clone representing myostatin be found in the cDNA library made from brain?

Express your answer as a probability.

Answer 1

Answer A.: Myostatin is a proteinous growth and differentiation factor also known as factor 8 is synthesized by MSTN gene which helps in the growth and differentiation of muscle cell in humans. Thats why MSTN gene is expressed only in muscle cells and does not produced in other human cells.The cytogenetic location of gene is 2q32.2, mean it is present on long arm of chromosome number 2 at position 32.2. The molecular location is in between base pairs of 190055700 to 190062729. This clearly indicates that the size of gene is approx 7029 bp. The average insert size in the genomic libraries is 100 kb which is greater than the size of MSTN gene (7029 bp).

This clearly indicates that the clone representing MSTN gene in a genomic library will be one only from a one set of the genome. This information is not sufficient to calculate the exact frequency in a genomic library prepared from the genome isolated from random muscle cell population.

Reference:

https://ghr.nlm.nih.gov/gene/MSTN#location

Answe B. : The average insert size in the genomic libraries is 100 kb which is greater than the size of MSTN gene (7029 bp). The MSTN gene is present in each and every cell including the brain cell, hence this clearly indicates that the clone representing MSTN gene in a genomic library of brain will be same as in muscle cell.

Answer C.: Myostatin is a proteinous growth and differentiation factor also known as factor 8 which helps in the growth and differentiation of muscle cell in humans. Thats why myostatin is expressed only in muscle cells and does not produced in other human cells. The cDNA library is prepared from the expressed mRNA which is not expressed in brain cell for myostatin, hence the probability is zero for clone representing myostatin be found in the cDNA library made from brain.