Natural Selection

Question 1

Define genetic diversity

Answer 1

The number of different alleles of genes in a population

Question 2

Define an allele

Answer 2

A different form of a gene

Question 3

Define an adaptation

Answer 3

A characteristic thatincreases an organism’s chance of survival/reproductive success

Question 4

What are three types of adaptation?

Answer 4

1) anatomical eg thick fur, layer of blubber for colder temps
2) Physiological eg presence of enzymes to aid in digestion or allow tolerance to extreme temps
3) Behavioural eg mating behaviours

Question 5

What is reproductive success?

Answer 5

An organism with increased reproductive success is more likely to:
i) survive until it reproduces
ii) grow sufficiently well to reproduce successfully
iii) attract a mate

Question 6

What is the process of natural selection?

Answer 6

1. Random mutations of a gene result in new alleles
2. This causes genetic variation within the population, as different individuals will have different combinations of alleles
3. All individuals in the population are subjected to selection pressures such as competition, predation and disease
4. There is differential reproductive success
5. Individuals with the advantageous allele combinations have improved reproductive success. They are more likely to survive selections pressure, reproduces and pass on the advantageous allele to their offspring - next generation
6. Process repeats over many generations
7. The frequency of the advantageous alleles in a populations gene pool increases from generation to generation
8. Natural selection results in species that are better adapted to their environment

Question 7

What are 2 random causes of low genetic diversity not due to natural selection?

Answer 7

1) genetic bottlenecks = events that cause a big reduction in a population, this reduces the number of different alleles in the gene pool and as a consequence there is low genetic diversity. Population then increases again but are all descended from only a few individuals so the genetics diversity is still low

2) Founder effect = when a small founder population had become isolated from the original population. They have a smaller gene pool and genetic diversity than the original population, when the new population increase in dice there will still be lower genetic diversity

Question 8

What are types of natural selection?

Answer 8

1) stabilising selection
2) directional selection

Question 9

What is stabilising selection?

Answer 9

Where individuals with alleles for phenotypic characteristics towards the middle of the range are more likely to survive, reproduce and pass on their alleles. Unfavourable alleles (leading to extreme phenotypes) become rarer and decrease in frequency in the population. Stabilising selection occurs when the environment is unchanging

eg human birth weight

Babies of medium birth weight are at a selective advantage and more likely to survive. Those carrying alleles for a low birth weight are less likely to survive after being born and those carrying alleles for a high birth weight are less likely to survive the process of being born

Question 10

What is directional selection?

Answer 10

Individuals with alleles which give a characteristic of an extreme type are more likely to survive and reproduce. The mean moves in the direction of the extreme. Directional selection is more common when the environment changes.

Eg antibiotics are substances which kill bacteria, in a population of bacteria only a few show the extreme characteristics of resistance to antibiotics. When the population comes into contact with an antibiotic only the few with the advantageous alleles surviv to reproduce and pass on the alleles to the next generation. After many generations most of the bacteria in the population will carry adaptive alleles which give them resistance to the antibiotic