3. MOLECULAR EVOLUTION Flashcards
1
Q
Define Natural Selection
A
- Natural selection refers to the effects of selection pressures & other factors on the frequency of heritable changes such as genetic variants
2
Q
Define fitness in terms of evolution
A
- Fitness refers to the ability to reproduce
- Genetic variants that increase fitness will be selected for & vice versa
3
Q
What four factors can affect genetic variation?
A
- SELECTION
- MUTATION/GENE FLOW
- MIGRATION
- GENETIC DRIFT
4
Q
What is Selection?
A
- Selection refers to genetic variants that confer a positive advantage being selected & passed on to the offspring & vice versa
- The frequency of genetic variants increases in the population
5
Q
What is a mutation?
A
- A mutation refers to a change or variation which arises in the genome
6
Q
How can migration lead to admixture?
A
- Migration involves the movement of one population into another, which introduces new genetic variants into the gene pool which is known as admixture
- In the original population, these genetic variants may have been neutral but could be disease causing when introduced into a new population
7
Q
What is genetic drift?
A
- Genetic drift refers to the random change in the frequency of genetic variants over time (it tends to decrease)
- All genetic variants can undergo genetic drift but neutral variants are more likely to undergo genetic drift as they don’t confer any negatives or positives
- Another reason is that we don’t pass on all our genetic variants to offspring due to recombination events
8
Q
- What is sequence conservation?
A
- Sequence conservation - some sequences are conserved as they are resistant to changes or mutations. This is because changes in these regions could be detrimental to function e.g developmental genes.
9
Q
What are the three levels of sequence conservation?
A
- HIGH = coding regions (exons)
- INETRMEDIATE = Promoter, 3’UTR , 5’UTR
- LOW = introns, 3rd base of codon
10
Q
- What are two benefits of sequence conservation?
A
- Create evolutionary profiles for genes & gene families
2. Identify important gene regions
11
Q
- What is Phylogenetics?
A
- Phylogenetics is the study of evolutionary relationships between species, organisms etc.
12
Q
What are phylogenetic trees?
A
- Phylogenetic trees aim to show the relatedness between species
- Close = more related
- Distant = less related
- Distance could be due to time or evolutionary pressures
13
Q
What is gene duplication & how does it occur?
A
- Gene duplication involves copying or duplicating a gene. It occurs due to unequal crossing over, where there’s recombination of similar but not identical sequences
- The duplicated gene will evolve a new function that is beneficial to the original or it will act as a pseudogene
- The original gene will continue to carry out it’s original function
14
Q
What are the two clusters of globin genes?
A
- there are 2 alpha & 2 beta gene clusters
- alpha = chromsome 16, 3 normal genes, 3 pseudogenes
- beta = chromosome 11, 5 normal gene, 1 pseudogene
15
Q
*How does globin gene expression change with time?
A
HbF is more common before birth but HbA is more common after birth. Beta levels increase before birth, gamma levels fall & alpha remains high
16
Q
How did the globin gene clusters evolve?
A
- Globin gene clusters evolved through gene duplications & mutations
17
Q
What are pseudogenes?
A
- Pseuodgenes are genes with no function, they can accumulate mutations which prevent them from carrying out their function.
- Pseudogenes reduce the risk of mutations occurring in more important genes.
18
Q
*What changes in genes cause Sickle cell disease?
A
- A single base change from GAG to GTG causes a substitution from Glutamic acid to Valine at position 6 in the beta globin gene
- Sickle cell disease is an autosomal reccessive disorder meaning that two copies of the gene are needed
- HbS is the Hb that arises as a result of this base change
19
Q
*What are the three main symptoms of Sickle Cell disease?
A
- Anaemia - jaundice, fatigue
- Increased frequency of infection due to spleen damage
- Acute pain episodes due to oxygen crisis
20
Q
Why did natural selection allow the SCD gene to eb passed on?
A
- Two copies of the SCD gene would lead to sickle cell disease & decrease fitness individuals would not live long enough to have children.
- BUT, one copy of the SCD gene provides immunity from malaria which is known as HETEROZYGOTE ADVANTAGE
- SCD is common in areas where malaria is prevalent, natural selection would have removed this variant but it confers the advantage of malaria resistance
