Chapter 13, Problem 1DAA

Summary Introduction

To explain: The number of Ty2 strain of Salmonella typhi that was able to enter normal cells than cells heterozygous for the ΔF508 allele.

Introduction: An allele is the modification of the gene. Salmonella typhi is the causative bacteria of typhoid. Cystic fibrosis (CF) is a genetic disorder caused due to the inability of the cell to perform endocytosis due to a mutation in the CFTR gene. Cystic fibrosis affects the lungs, intestine, liver, and kidneys. Endocytosis is a phenomenon where the cell takes up molecules by engulfing with its membrane. The S. typhi exploits this mechanism to infect the intestinal cell and causes diarrhea. The cells that are homozygous for this CFTR mutation cannot perform endocytosis, and the S. typhi cannot infect those individuals.

Explanation of Solution

Scientist G along with his colleagues studied the uptake of S. typhi by two types of epithelial cells:

• Cells that are homozygous for the normal alleles.
• Cells that are heterozygous for ΔF508 allele associated with CF and the normal alleles.

Cells that are homozygous for the mutant allele do not take up S. typhi; therefore, those cells were not chosen. A bar graph was drawn with three strains of S. typhi on the X-axis, and the number of bacteria internalized by both types of cells in the Y-axis.

Approximately, 600,000 S. typhi entered the normal cells that are homozygous for the normal alleles.

Approximately, 80,000 S. typhi entered the mutated cells that are heterozygous for ΔF508 allele associated with CF and normal alleles.

Therefore, the number of times more S. typhi entered normal cells than heterozygous cells can be calculated as follows:

$\begin{array}{c}\text{Number of}\text{times more}S.typhi\text{ entered normal cells}=\frac{600000}{80000}\\ =7.5\end{array}$

Conclusion

Therefore, about 7.5 times more S. typhi entered the normal cells.