Chapter 7, Problem 21EQ

Summary Introduction

To analyze:

A scientist has numerous various strains of $\text{T4}$ phage that has only mutation in the same gene. This mutation makes these strains temperature-sensitive. i.e. they cannot proliferate themselves when E. coli is developed at $\text{37°C}$ but phages can proliferate when the E. coli is developed at $\text{32°C}$. Question asked to suggest an experimental approach to map the temperature- sensitive mutations, considering Benzer’s approach for intragenic mapping.

Introduction:

The genes that are closer enough on the same chromosome are called linked, whereas the genes that are found on different chromosomes, occasionally far apart but on the same chromosome are called unlinked. Genetic linkage is a physical relationship among genes that are located close TO one another on a chromosome. Recombination among linked genes of homologous chromosomes occurs significantly less than $\text{50\%}$ of meiotic division and more than $\text{50\%}$ gametes have parental combinations of the alleles. The Recombination frequency differs among linked genes and is roughly proportionate to the distance between genes on a chromosome.

Recombination frequency is the proportion of a number of recombinant offspring resulting in a genetic cross between two organisms.

A linkage map is a map of chromosome based on recombination frequency. Distance between the genes is expressed in “map units”.

One map unit or Centi-morgan (CM) denotes $\text{1\%}$ recombination frequency.

The recombination frequency (r) of the syntenic gene is estimated by the formula

$\text{r=}\frac{\text{Number of recombinant}}{\text{Total number of progeny}}$

Recombination frequency expresses the distance among genes. Least the recombination frequency, closer the genes are, while greater recombination frequencies show that the gene distance is more.