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GEN > 3. MOLECULAR EVOLUTION > Flashcards

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
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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

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3
Q

What four factors can affect genetic variation?

A
  1. SELECTION
  2. MUTATION/GENE FLOW
  3. MIGRATION
  4. GENETIC DRIFT
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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
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5
Q

What is a mutation?

A
  • A mutation refers to a change or variation which arises in the genome
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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
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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
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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.
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9
Q

What are the three levels of sequence conservation?

A
  1. HIGH = coding regions (exons)
  2. INETRMEDIATE = Promoter, 3’UTR , 5’UTR
  3. LOW = introns, 3rd base of codon
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10
Q
  • What are two benefits of sequence conservation?
A
  1. Create evolutionary profiles for genes & gene families

2. Identify important gene regions

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11
Q
  • What is Phylogenetics?
A
  • Phylogenetics is the study of evolutionary relationships between species, organisms etc.
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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
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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
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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
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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

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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
  1. Anaemia - jaundice, fatigue
  2. Increased frequency of infection due to spleen damage
  3. 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

GEN (18 decks)

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