Chapter 10, Problem 23P

Summary Introduction

To analyze:

A DNA fragment is hybridized by two probes $\text{-A}$ and B respectively. These probes hybridize near one another in the region of DNA with length variation after digested with restriction enzyme Hind III.

The four resultant maps are illustrated below that show the positions, intermediate distances in “Kb” (kilobases), and the binding locations of probes with DNA. The maps correspond to alleles ${\text{H}}^{\text{1}}\text{to}{\text{H}}^{\text{4}}$.

1. In autoradiography, for genotype ${\text{H}}^{\text{1}}\text{to}{\text{H}}^{\text{3}}$ - which DNA bands are expected for probe A, B and for both probes together?

2. In autoradiography, for genotype ${\text{H}}^2\text{to}{\text{H}}^4$ - which DNA bands are expected for probe A, B and for both probes together?

3. If a child is born to a woman having genotype ${\text{H}}^{\text{1}}\text{to}{\text{H}}^{\text{3}}$ with a man having genotype ${\text{H}}^2\text{to}{\text{H}}^4$. The four probable genotypes for a child is to be found.

4. What are expected DNA bands for each possible genotype for a child of this couple using probe A and B respectively?

Introduction:

Blotting is the technique routinely used for the detection of biomolecules such as DNA, RNA, and proteins, named as Southern blotting, northern blotting, and western blotting respectively. In southern and northern blot method, the DNA and RNA are separated on agarose gel electrophoresis and then detected by using the DNA probe complementary to the targeted sample. Southern blotting is a technique used to identify the target gene arrangement within a mixture of several genes. In $1975$, Edwin Southern introduced this system. The goal of southern blotting is to detect if a sample of the genome contains a complementarity with the specific probe.

In autoradiography, the radioactively labelled substances with radioisotopes are used. In a bio-analytical procedure, such substances that are distributed in a biological sample are visualized. It is an $\text{X-ray}$ image resulting from a pattern of decay radiation (beta or gamma rays). It generates a perpetual record of locations of relative potencies of radiolabeled bands in a gel or blot.

The first observation was recorded by Niepce de St. Victor. It was obtained accidentally when blackening occurred on the emulsion of silver chloride and Iodide by Uranium salts, and the first autoradiography used in a biological experiment traced the distribution of polonium in the specimens.

DNA preparations from different individuals normally show different patterns of the size distribution of restriction fragments that hybridize with a particular probe. These differences are called restriction fragment length polymorphisms (RFLPs). RFLP technique involves cutting a particular region of DNA with known variability, with restriction enzymes, then separating the DNA fragments by agarose gel electrophoresis, and determining the number of fragments and relative sizes.