Genetic diversity and Natural selection

Question 1

What is genetic diversity

Answer 1

Small differences in DNA base sequences transferred between generations within a species

It is the number of different alleles of genes in a population

factor enabling natural selection to occur

Question 2

What do Mutations result in in terms of genetic diversity what does it contribute to

Answer 2

Results in the generation of new alleles and contributes to genetic diversity and the size of the gene pool

Question 3

What effects may new alleles have in a population

Answer 3

• New alleles may be advantageous, disadvantageous or have no apparent effect on phenotypes (due to the genetic code being degenerate)
• New alleles can also remain hidden in a population for several generations which will then contribute to phenotype variations

Question 4

What is selection pressure

Answer 4

Environmental factors that affect the chance of survival

They increase the chance of individuals with a specific phenotype surviving and reproducing

Question 5

What do favoured phenotypes do

Answer 5

They create a higher fitness

Question 6

What is fitness and higher fitness

Answer 6

Fitness - The ability to survive and pass on its alleles to offspring

Higher fitness - Adaptations that make them better suited to their environment

Question 7

What is a gene pool

What happens if you have a large and small gene pool

Answer 7

The collection of all genes and alleles in a population at a particular time

• Large gene pool - High genetic diversity and Strong ability to adapt to change
• Small gene pool - very low genetic diversity and less able to adapt to change so have a higher vulnerability to extinction

Question 8

What is natural selection and explain what happens

Answer 8

• Random mutations can produce new alleles of a gene
• Many mutations are harmful or neutral but under certain environmental conditions, the new alleles may benefit the possessor. Organisms with theses alleles have an increased chance of survival and reproductive success
• The advantageous allele is passed onto the next generation
• Over several generations the new alleles increase the allele frequencies in the population

Question 9

What are other factors or processes that can effect allele frequencies in a population

Answer 9

• Founder effect
• Genetic drift
• Bottleneck effect

Question 10

What is the founder effect

Answer 10

Occurs when a small number of individuals from a large population start a new population
- Only some of the total alleles from the parent population will be present
- Not all of the gene pool will be present in the smaller population
- Alleles in the new founding population is due to chance
- As a result changes in allele frequencies may occur in different directions in smaller populations

Question 11

What is genetic drift

Answer 11

When a population is significantly small, chance can effect which alleles get passed on
- Over time some alleles can be lost or favoured by chance
- When there is a gradual change in allele frequencies in a small population due to chance not natural selection genetic drift occurs

Question 12

What is the bottleneck effect

Answer 12

Similar to the founder effect it occurs when a previously large population suffers a dramatic fall in numbers
- This reduces the genetic diversity as alleles are lost
- Surviving individuals end up reproducing with close relatives

Question 13

What causes different types of selection and what causes them

Answer 13

Selection pressures can have different effects on the allele frequencies of a population through natural selection

Types of selection:
- Stabilising
- Directional

Question 14

What is stabilising selection

What is an example

Answer 14

• Natural selection that keeps allele frequencies constant over generations
• Things stay as they are unless there is a change in environment
• Can be seen in human birth weights
  . Very low and very high birth rates are selected against leading to the maintenance of the immediate birth weights

Question 15

What is a Directional selection

What is an example ( no detail )

Answer 15

• Natural selection that produces a gradual change in allele frequencies over several generations
• Mean shifts (extreme type are more likely to survive)
• Usually happens when there is a change in environment/selection pressures or a new allele has appeared that is advantageous
• For example antibiotic resistant bacteria

Question 16

Explain how antibiotic resistance is a directional selection

Answer 16

• Prescence of antibiotics is a selection pressure
• Mutations are occurring in bacteria populations randomly
• Bacteria with this resistant mutation are more likely to survive and reproduce and most bacteria with out this resistance die
• Overtime this leads to an increase in the frequency of the beneficial allele that produces antibiotic resistance.