Genetic Diversity (complete)

Question 1

Describe the two ways in which meiosis helps produce genetic variation.

Answer 1

Crossing over:
- during prophase 1, individual chromosomes of each homologous pair come into association with each other (forming bivalents/chaisms), where they twist, forming new allele combinations.

Independent Segregation of Homologous Chromosomes:
- during metaphase 1, lining up of homologous chromosomes is done randomly, therefore when they are pulled apart, the combination going into the daughter cells is also random.

Question 2

Define mutation and the cause(s).

Answer 2

Mutation - any change in the amount or structure of the DNA of an organism, usually occurring naturally and randomly.

Cause(s) - environmental factors that increase the rate of mutation (mutagens - e.g: high energy radiation, mutagenic chemicals.)

Question 3

What are point mutations?

Name the three types.

Answer 3

Point mutations - involves a change of only one nucleotide at a particular locus.

• Substitution: one nucleotide is replaced by another with a different base.
• Addition: an extra nucleotide is added, so an extra base is added to the sequence.
• Deletion: one nucleotide is removed.

Question 4

How can a substitution mutation affect the sequence of genetic material?

Answer 4

• only affects one codon in a sequence of genetic material, therefore only affects the outcome of one amino acid.
• 3 types:
  > nonsense mutation - creates a stop codon.
  > mis-sense mutation - changes a single amino acid.
  > silent mutation - different codon but codes for same amino acid (degenerate code).

Question 5

How can addition/deletion mutations affect the sequence of genetic material.

Answer 5

• causes a frame shift, as every right-hand nucleotide moves one space left or right, affecting every/most adjacent amino acids due to different triplet codes.
• frame shift affects the primary structure of protein, therefore the tertiary structure due to changes in the bonds.

Question 6

Describe the two types of chromosomal mutation.

Answer 6

Polyploidy -
- found in plants, changes in whole sets of chromosomes, so organisms have 3 of more sets of chromosomes instead of the usual 2 sets.

Non-disjunction -
- during meiosis, changes in the number of individual chromosomes, either found during meiosis 1 or meiosis 2, causing two types of outcome.

Question 7

Define:

• Biodiversity
• Species richness
• Species diversity
• Genetic diversity
• Ecosystem diversity

Answer 7

Biodiversity - describes variety in the living world.
Species richness - the number of different species.
Species diversity - the number of different species and the abundance of each species within a community.
- (the higher the species diversity, the more stable the ecosystem and the less affected by climate change it is.)
Genetic diversity - the variety of genes possessed by individuals that make up any one species.
Ecosystem diversity - the range of different habitats within a particular area.

Question 8

Describe Biodiversity in:
- harsh environments
- less harsh environments

Answer 8

Harsh -
- in extreme conditions, the biodiversity is normally low, only a few species will have the necessary adaptations to survive.
- here the ecosystem in unstable and dominated by climate factors rather than the organisms within the community.

Less Harsh -
- the species diversity is normally high in a habitat such as a rainforest where conditions are less harsh.
- here the ecosystem is stable, and dominated by the organisms within the community rather than the climate factors.

Question 9

How do you measure/calculate species diversity?

Answer 9

Using the Index of Diversity:

d = N(N-1) / sum of (n(n-1))

where N = total number of organisms of all species.
and n = total number of one species.

Question 10

Define:

• Reproductive success
• Allele frequency

Answer 10

Reproductive success - Individuals that have favourable alleles which make them better adapted to an environment are more likely to survive and so reproduce.

Allele frequency - How often a particular allele occurs within a population.

Question 11

Describe of the two types of selection during Natural selection.

Answer 11

Directional selection -
- occurs when the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive, therefore breed and produce offspring.

Stabilising selection -
- the phenotypes with successful characteristics are kept. If the environment stays the same then the individuals closest to the mean are favoured because they have the alleles that have given them a survival advantage.

Question 12

Name three types of evolution due to natural selection.

Answer 12

• Anatomical: shorter ears, thicker fur etc…
• Physiological: oxidising of fat rather than carbohydrates etc…
• Behavioural: autumn migration instead of spring etc…

Question 13

Name three types of evolution due to natural selection.

Answer 13

• Anatomical: shorter ears, thicker fur etc…
• Physiological: oxidising of fat rather than carbohydrates etc…
• Behavioural: autumn migration instead of spring etc…