Genes (3.1)

Question 1

Gene

Answer 1

A heritable factor which controls a specific characteristic. Length of DNA.

Question 2

Locus

Answer 2

The locus is the position on a chromosome where a gene for a specific trait is located.

Question 3

Alleles

Answer 3

Alternative forms of a gene that code for different variations of a specific trait. They differ from each other by one or a few bases.

Question 4

What is a gene mutation?

Answer 4

A change in the nucleotide sequence of a section of DNA coding for a specific trait. New alleles are formed by mutation.

Question 5

Types of gene mutations

Answer 5

Neutral - no effect on the function of the organism i.e. silent
Harmful - may alter the survival capacity of the organism
Beneficial - a mutation that changes the gene sequence to create new variations of a trait. They form the basis of evolution and improve the survival of an organism.

Question 6

Causes of mutations

Answer 6

Spontaneous mutations - arise from errors in DNA replication.
Induced mutations - can be induced by mutagens.
(eg. Physical mutagens - x-ray radiation, chemical mutagens - processed foods, biological mutagens - viruses).

Question 7

Locations of mutations

Answer 7

Somatic cells - not inherited and restricted only to the affected tissue in that organism.
Gamete (sex) cells - can be inherited and will affect all cells in the offspring.

Question 8

Cause of sickle cell anaemia

Answer 8

Sickle cell anaemia is caused by a base substitution mutation where GAG mutates to GUG which changes the amino acid from glutamic acid to valine. This causes the haemoglobin to form insoluble fibrous strands which changes the shape of the red blood cell to a sickle shape. Sickle cells may form clots within the capillaries, blocking blood supply to vital organs. They are also destroyed more rapidly than normal cells, leading to a low red blood cell count (anaemia).

Question 9

Genome

Answer 9

The whole of the genetic information of an organism. The human genome consists of:
- 46 chromosomes
- 3 billion base pairs
- 21,000 genes

Question 10

Describe the Human Genome Project (2003) and its applications.

Answer 10

An international cooperative venture to sequence the entire human genome. The Project helped to screen people for known genetic conditions, establish ancestral lineages and discover pharmaceutical treatments.