9.3 natural selection

how does variation affect allele frequency

results from mutations and inheritance of different combinations of genes. occurs during the crossing over during meiosis.

who was natural selection proposed by

Charles Darwin and alfred wallace

define natural selection

where organisms with favourable variations survive and reproduce, passing on these genes to the next gen

what happens to species with unfavourable characteristics

they don’t survive to reproduce, therefore genes are not passed on

what are the 3 observations with natural selections theory

variation: passed on from generations, members of diff species differ in characteristics
birth rate: organisms reproduce at a higher rate than resourced
natures balance: species number remains constant

what is ‘survival of the fittest’

due to excessive birth rate and limited resources, the species with favourable characteristics (due to variation) will survive, reproducing.

explain the principle of evolution through natural selection

species with favourable characteristics better suited have a higher chance of surviving and reproducing. This means the gene pool will have a higher proportion of alleles that produce favourable characteristics

how does large population size influence evolution

• more variations in the gene pool

• Evolution occurs slowly

• Most changes are adaptive

• Individuals make a small contribution to the gene pool

how does small population size influence evolution

• less variation in the gene pool

• Individuals make a large contribution to the gene pool

• Evolution can occur rapidly

• Many changes are non adaptive

how does natural selection result in humans

Results gradually becoming better adapted to the environment

define adaptation

any characteristic that helps an organism to survive and reproduce in its environment

how is sickle cell anemia an example of natural selection

it is a point mutation that alters the haemoglobin structure . The heterozygous form of sickle cell anemia gives protection from malaria. Therefore the allele frequency in malaria affected areas is higher as it gives a survival advantage.