Changing population characteristics (h,g)

Question 1

What are selection pressure?

Answer 1

Selection pressures are factors that affect the organisms chances of survival or reproductive success (ability to produce fertile offspring), e.g. predation, competition, disease.

Question 2

The process of natural selection

Answer 2

1. organisms within a species show variation - caused by genetic variation
2. organisms whose characteristics are best adapted to a selection pressure have an increased chance of surviving + successfully reproducing (SOTF)
3. successful organisms pass the allele encoding the advantageous characteristic onto their offspring
4. repeated over every generation, so over time the proportion of individuals with the advantageous adaption increases, so the frequency of this allele increases in the gene pool.
5. over many generations this process can lead to the evolution of a new species

Question 3

Describe antibiotic resistant bacteria as evidence for evolution

Answer 3

• evolution over a short time due to rapid reproduction, so mutation can occur and spread easily
• resistant individuals survive and reproduce, passing the allele on to offspring while non-resistant individuals die
• so the resistant individuals in a population increased
• e.g. MRSA: Methicillin-resistant Staphyloccus aureus

Question 4

Describe moths as evidence for evolution

Answer 4

• peppered colour provided camouflage against light-coloured tree bark, so increased the chanced of survival, while the dark moths were eaten
• Industrial revolution caused trees to darken, so dark moths were better adapted, so survived and reproduced, increasing their frequency (and the frequency of the allele) in the population

Question 5

Describe pesticide resistance in insects as evidence for evolution

Answer 5

• pesticides are used to kill insects
• individual insects with resistance survived + passed on characteristic through their alleles, allowing evolution of a resistant population
• sometimes pre-adaptation occurs - when an organism’s existing trait is advantageous for a new situation - contributing to the development of other pesticide resistance