Variations• Starter activity

• Explain the following terms

• Alleles, locus, chromosomes, hetrozygous chromosomes, homozygous chromosomes, genes, and species

Variations • Learning objectives

• To determine between ‘continuous’ and ‘discontinuous’ variations

• To understand that a ‘single’ gene inheritance leads to ‘discontinuous’ variations

• To appreciate that ‘polygenic’ inheritance leads to ‘continuous’ variations

Variations• List the ‘similarities’ and ‘differences’ between

the human species

• List those differences in to 2 categories ‘continuous’ variation and ‘discontinuous’ variation

• List inherited features which can be affected by the environment

Discontinuous variation

• Discontinuous variations relates to a feature which is clear cut (either you have it or not) e.g. rolling of tongue, ear lobe shape, thumb hyperextension. Theses are determined by the alleles of a single gene, no measurements are needed to distinguish between them. Sketch a graph to show the results for the following variations……………………….

Discontinuous variations

Tongue roll Non-tongue roll

15 5

Ear lobe Non-ear lobe

10 10

Bend thumb

Non-bend thumb

13 7

Continuous variations• Continuous variations relates to features which

are determined by polygenes (many genes) e.g. eye colour, hair colour, skin colour, height, and shape of head. These are variations are greatly influenced by the environment

• Explain which of the above features and their environmental factors which could influence them

Continuous variations• Sketch a graph from the following results

Eye colour No. of people

Green 3

Brown 7

Grey 3

Hazel 5

Blue 4

Hair colour No. of people

Black 10

Brown 2

Ginger 3

Red 4

blonde 1