DNA fingerprinting

The use of promoters being transferred along with desired genes in gene technology

In the DNA of bacteria, other prokaryotes and most genes in eukaryotes, there is a non-transcribed sequence of DNA bases that marks the beginning of the gene and identifies the point at which transcription begins.  It is found just before each gene.  In prokaryotes, it usually consists of two short six base sequences CTATAAT ten bases before the gene and TTGACA 34 bases before the gene.  The presence of at least one of these is usually necessary to initiate transcription of the gene.  Therefore, if a gene is transcribed into prokaryotic DNA without adding a prokaryotic promoter, it will not be transcribed and expressed.  In addition, in eukaryotes, the regulation of gene expression is more complex and so transferring a eukaryotic promoter to be used in a prokaryotic cell may not have the intended effect.  Eukaryotic promoters can be used in eukaryotic cells but care must be taken to ensure that all of the relevant code is included.

DNA Fingerprinting and DNA Sequencing

DNA Fingerprinting

DNA fingerprinting, also called DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing, in genetics, is a method of isolating and identifying variable elements within the base-pair sequence of DNA (deoxyribonucleic acid). The technique was developed in 1984 by British geneticist Alec Jeffreys, after he noticed that certain sequences of highly variable DNA, which do not contribute to the functions of genes, are repeated within genes. Jeffreys recognized that each individual has a unique pattern of thee sequences (the only exceptions being multiple individuals from a single zygote, such as identical twins).

These highly repetitive sequences are referred to as variable number tandem repeats (VNTR).  The number of repeats and hence their size varies markedly between individuals and is inherited half from the mother and half from the father.

Steps involved in DNA fingerprinting

1.    DNA is separated from any body cell.  It is usually obtained from semen, white blood cells or hair roots.

2.    Restriction enzymes are used to cut the DNA close to but not within the VNTR regions to release them intact.

3.    Electrophoresis is used to separate the fragments according to size.

4.    4.  The fragments are transferred to a nylon membrane and heated to make the DNA single stranded.

5.    A radioactive DNA probe with a base sequence complementary to one of the VNTR sequences is used to locate particular bands.  It binds to the fragment containing DNA complementary to the probe.

6.    Excess probes and any DNA not bond to a probe is washed off.

7.    X-ray film is now placed over the nylon membrane where β-emissions from the radioactive probe will blacken the film so that the final product is a pattern of dark and pale strips on an x-ray film.

Answers

1.     Child 4 is adopted since none of the child 4’s bands match in position with the Mom’s or Dad’s bands.

2.    Child 2 is from the mother’s previous marriage because 3 of Child 2’s bands match the position of the mother’s bands but non match the Dad’s.

3.    Child 1 and Child 3 are the own children of Mr and Mrs Chan because half of their bands match the Mom’s bands and the other half match the Dad’s bands.

DNA sequencing