6.1 Forensic Biology

Question 1

Intron

Answer 1

A non-coding section of DNA, it does not give rise to an amino acid sequence. These non- coding pieces of DNA often contain short sequences of bases that are repeated many times. Analysis of these repeated sequences forms the basis of DNA fingerprinting.

Question 2

Exon

Answer 2

A coding section of DNA that gives rise to an amino acid sequence. During transcription the entire gene is copied to form pre-mRNA including exons and non-coding introns. During
splicing the introns are removed and the exons, the expressed regions, are joined to form the mRNA.

Question 3

Micro-satellite, Micro-satellites, Short tandem repeats

Answer 3

A short sequence of repeated DNA bases. Some DNA is non-coding and does not give rise to an amino acid sequence. Non- coding DNA often contains short sequences of two to four bases that are repeated many times. These repeating sequences are called micro- satellites or short tandem repeats

Question 4

Polymerase chain reaction,

Answer 4

PCR A reaction used to multiply DNA samples. The sample is passed automatically through a cycle of reactions in which the DNA is split into its two strands and replicated. Under the influence of the enzyme DNA polymerase, new complementary strands are synthesised from nucleotides which are added to the reaction tube.

Question 5

DNA primer

Answer 5

A small piece of single-stranded DNA. It acts a signal, binding to and marking the piece of DNA which is to be copied in the polymerase chain reaction (PCR).

Question 6

DNA polymerase

Answer 6

An enzyme that catalyses the joining together of individual nucleotides to form a molecule of DNA. DNA polymerase is essential to the process of DNA replication. It is also important in gene technology where it is used in the polymerase chain reaction (PCR) to produce a large number of identical copies of small pieces of DNA.

Question 7

Gel electrophoresis

Answer 7

A technique used to separate fragments of DNA. The DNA fragments are placed on a jelly-like substance (a gel) that provides a stable medium through which the DNA molecules can move. The gel is connected to electrodes that produce an electrical field and the DNA fragments migrate in the field according to their overall charge and size. Smaller fragments travel faster and therefore further in a given time

Question 8

Restriction enzyme, Restriction endonuclease

Answer 8

One of a group of enzymes which is able to cut a DNA molecule at particular points along its length. Each restriction enzyme recognises a specific base sequence and will only cut a DNA molecule where this sequence occurs. Restriction enzymes are very important tools in genetic engineering. They can be used, for example, to isolate particular genes and insert them into the DNA of another organism. Restriction enzymes are also known as restriction endonucleases.

Question 9

Sigmoid curve S

Answer 9

-shaped line on a graph. Many biological processes follow a sigmoid curve including increases in population sizes from initially low levels and decreases in the body temperatures of warm-blooded animals after death.

Question 10

Autolysis

Answer 10

Self-destruction of cells. The breakdown of the tissues of an organism which occurs after its death. It is caused by the action of enzymes from the gut and from the lysosomes. These enzymes bring about decomposition by breaking down the organism’s own cells. Autolysis also occurs during normal development of organisms, for example fingers are separated by autolysis of the tissue between adjacent fingers.

Question 11

Factors that determine post mortem cooling

Answer 11

• body size + position
• clothing
• air movement
• humidity
• temperature of surroundings