Source:http://www.biology-resources.com

1. SOURCE OF VARIATION: MUTATION Is a change in a gene orchromosome

3. 22 Chromosome mutations in humans usually result in spontaneous abortion of the foetus But a proportion survive e.g. Downs syndrome: The affected person has one extra chromosome in their genome (i.e. 47 instead of 46 chromosomes) This results in characteristic facial features, varying degrees of mental impairment and, usually, a very cheerful disposition Klinefelters syndrome. The affected male has an extra X chromosome (XXY) The person appears to be a normal male but he is infertile Chromosome mutations in humans

4. 25 -A mutated gene which is dominant, or inherited as a homozygous recessive, will affect the whole organism -A mutated gene which does not result in abortion or early death of an organism will be inherited by the offspring -Very rarely, a mutation will be beneficial and will be inherited by the offspring Gene mutations in humans may result in: Albinism Sickle cell anaemia Haemophilia Cystic fibrosis Dwarfism Colour blindness Mutations

6. 30 Mutagens Some environmental effects may increase the mutation rate. These include radiation (X-rays, ultra-violet, radioactive materials) and carcinogenic chemicals such as those in tobacco smoke These are all known as mutagens -Mutagens which affect body cells may produce cancers. -Mutagens affecting the reproductive organs may result in defective offspring

7. Question 1 35 Chromosome mutations can occur as a result of… (a) gain of an extra chromosome (b) doubling of the entire set of chromosomes (c) faulty replication of DNA (d) breaking of a chromosome

8. 36 Question 2 Gene mutations can occur during DNA replication prior to … mitosis (b) meiosis

9. Question 3 37 Sickle cell anaemia results from … a change in a nucleotide triplet (b) a change in a single nucleotide (c) a change in a single amino acid (d) a chromosome mutation