Week 7: Evolution and population genetics

Question 1

What factors contribute to evolution and population divergence?

Answer 1

• Mutation
• Recombination and rearrangement
• Genetic drift
• Natural selection
• Bottlenecks and Founder effect
• Admixing and gene flow

Question 2

Mutation

Answer 2

Mutation rates aren’t always steady, not all bases change (eg. ionising radiation)

Question 3

Divergence over time

Answer 3

The probability of a mutation is influenced by the likelihood that the particular error will occur and the likelihood that it will be repaired

Question 4

Recombination and rearrangement

Answer 4

• Homologous recombination results in the re-assortment of genes between chromosome pairs without altering the arrangement of genes within the genome
• Recombination can change what genetic variants are inherited together, which can have important implications for genetic research, as well as increasing genetic diversity within the population

Question 5

Population size

Answer 5

• In small populations, the frequency of a mutation will change randomly and new mutations are likely to be eliminated by chance
• Fixation - the process by which a new allele that replaces the allele that was previously predominant in a population
• The frequency of a neutral mutation largely depends on genetic drift, the strength of which depends on the size of the population
• The frequency of a mutation that affects the phenotype will be influenced by negative or positive selection

Question 6

Genetic isolates

Answer 6

• Small isolated populations generally show an increased frequency of rare or population disorders due to increased mating between close relatives (consanguinity) or among members of the genetic isolate (inbreeding)
• Monogenic disorders are less likely to show allelic heterogeneity in isolated populations than in more heterogeneous populations
• Polygenic disorders are likely to show a reduced number of loci/genes making them easier to study
• The Bedouin-Arabs of Israel are a well-studied isolate population. The population consists of about 90,000 individuals, divided into numerous tribes

Question 7

Natural selection

Answer 7

• The probability of a mutation is influenced by the likelihood that the particular error will occur and the likelihood that it will be repaired

Question 8

Synonymous mutation

Answer 8

A change in DNA sequence in a coding region that does not alter the amino acid that is encoded

Question 9

Nonsynonymous mutation

Answer 9

A change in a DNA sequence in a coding region that alters the amino acid that is encoded

Question 10

Genetic bottleneck

Answer 10

A genetic bottleneck or a population bottleneck is a sharp reduction in the size of a population due to environmental events such as famines and floods, or human activities such as population planning

Question 11

Founder effect

Answer 11

The founder effect is the less of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population

Question 12

Slippage mispairing mechanism

Answer 12

1. Starting (template) strand of genomic DNA
2. Replicating strand detaches incorrectly from template during replication
3. Replicating strand slips from its proper alignment with the template strand by one repeat
4. Mismatched repeat loops out
5. Newly synthesised strand contains an extra repeat

Question 13

Admixing and gene flow

Answer 13

Genetic admixing occurs when previously diverged or isolated genetic lineages mix. Admixture results in the introduction of new genetic lineages into a population

Question 14

Example of natural selection

Answer 14

• 1.6 - 1.8% of the Eurasian genome
• One gene of the BNC2 is involved in skin pigmentation, light skin is an advantage at higher latitudes because it is more efficient at generating vitamin D from sunlight, so could be an explanation for this.
• Chromosome regions with reduced Neanderthal ancestry are enriched in genes
• Genes involved in reproduction showed a 5 fold reduction of Neanderthals DNA compared to the rest of the genome, implying active natural selection

Question 15

Current genetic structure of Europe

Answer 15

• In genetics, principle component of analysis (PCA) can be used to produce new composite variable (principle components) that give an insight into how genetically similar people within the study population are to each other. Making it a useful tool for studying population structure and historical migration patterns