Question

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3. Application of DNA gel electrophoresis. DNA gel electrophoresis is commonly used in determining familial relationships among individuals, for ex; to establish paternity of a child. This technique is called DNA fingerprinting. In this technique the DNA of parents and children is roughly chopped up into pieces and resolved on an agarose gel. The DNA ill resolve according to their sizes and create a pattern or a "fingerprint". The fingerprint of the child is a combination of fingerprints of mother and father In the below case, a DNA fingerprint of a family was generated using DNA samples from the father, mother and 6 of their children. Help us determine the relationships between the various family members by studying the gel picture below. F M D1 S1 S2 D2 S3 D3

Answer 1

• During process of electrophoresis, DNA samples are detected using certain dyes, as they are colorless.
• DNA possess a net negative charge due to negatively charged phosphate in the structure. Thus, moves towards the anode.
• The pores of the gel plays a crucial role in segregating a molecule according to its size or molecular weight.
• To match the familial relationship between the children and the parents, the DNA samples from each individual are isolated.
• The sample may be subjected to digestion with restriction enzyme, which will migrate in the gel (as per their size, molecular weight, etc.) and may be observed as bands.
• If the child is biologically related to both parents, or any of the parents, the bands obtained will match to the parent's sample accordingly.
• If the child is not genetically related to the parents, the bands will not match.

Thus, from the results:

A. S1 and S3 are biological children of the parents.

They share bands with both parents

B. D1 and S3 share the same mother but have different fathers.

They share bands with mother, but not with father.

C. D2 and S3 are not related by genetics.

Their bands do not match with the parents or other children.

D. D3 and S1 have same father but different mothers.

They share bands with father, S1 has similar band to given mother, but do not match to D3 (having different mothers).

E. S1 have different father than one shown in the gel.

Share bands with mother, but not with father given.

F. D3 have different mother than one shown in the gel.

Share bands with father, but not with mother given.

G. D2 is not related to either of the parents or other children, except S2.

H. D2 and S2 are adopted.

As they are not related to either of the parents or other children.

I. If the DNA was not chopped and run, a single band would be obtained, that would not match even to the genetically related children.