7- Molecular Evolution

Question 1

define fitness

Answer 1

how well a species can reproduce in an environment

Question 2

define natural selection

Answer 2

the effects of a wide range of factors on the frequency of heritable changes within a species

Question 3

define evolution

Answer 3

the change in heritable characteristics of populations over successive generations

Question 4

define modern synthesis

Answer 4

how evolution and genetics together explain the molecular processes underlying evolution

Question 5

what four main factors affect the frequencies of genetic variants?

Answer 5

mutation, selection, migration and genetic drift

Question 6

how does selection affect the frequency of a genetic variant?

Answer 6

positive selection occurs if a genetic variant contributes to the survival or gives an advantage to a species - e.g. disease resistance gene, altering appearance to attract more mates (increases fitness)

some regions of genomic sequences are conserved and resistant to change

Question 7

how does mutation affect the frequency of a genetic variant?

Answer 7

mutation introduces genetic variants. if it is deleterious, it is selective against (negative selection) and over time is removed from the population.

Question 8

how does genetic drift affect the frequency of a genetic variant?

Answer 8

genetic drift = frequency of a genetic variant changes due to chance, making the frequency more arbitrary

can occur through genetic recombination events

Question 9

how does migration affect the frequency of a genetic variant?

Answer 9

migration can result in admixture - when two individuals from different populations interbreed. this can result in a new pool of variants being introduced into an existing pool, which can change genetic frequencies.

Question 10

define sequence conservation

Answer 10

sequence conservation occurs when there’s very little variation in a DNA sequence over time as it’s vital to an organism’s survival ; remains conserved

Question 11

what chromosome is the alpha globin gene cluster on? how many genes and pseudogenes does it have?

Answer 11

on chromosome 16
3 genes
3 pseudogenes

Question 12

what chromosome is the beta globin gene cluster on? how many genes and pseudogenes does it have?

Answer 12

chromosome 11
5 genes
1 pseudogene

Question 13

what are the specific levels of conservation and where do they occur in genes?

Answer 13

three levels - high, intermediate and low levels of conservation

high = occurs in coding regions

intermediate = UTR regions, promoters

low = introns, with the base of codons that are subject to change (if changing a base won’t change the final protein produced)

Question 14

what is the importance/use of sequence conservation?

Answer 14

establish evolutionary profiles

identify important regions of a gene that may code for an important protein

Question 15

what is phylogenetics?

Answer 15

phylogenetics is the study of evolutionary relationships between biological entities - species, individuals, genes

Question 16

what are the 4 steps in establishing a phylogenetic model?

Answer 16

observing DNA sequences in a group of organisms

looking at conserved or very similar sequences to construct evolutionary relationships. the less changes, the more closely related two entities are.

learning about evolutionary pressures that may have separated different groups

developing an evolutionary model in the form of a phylogenetic tree. the more organism observed, the more detailed the tree will be.

Question 17

what is a phylogenetic tree and what can it be used for?

Answer 17

a phylogenetic tree illustrates how relate different species/ DNA sequences are - the closer two entities are, the more closely related

the distance between entities can be used to measure mutation rates as a result of evolutionary pressures and time.

Question 18

describe the relationship between molecular evolution with respect to the globin gene

Answer 18

there are many different globin gene clusters - alpha, beta, delta, epsilon, zeta, myoglobin - which have emerged as a result of divergence from gene duplication of one ancestral molecule. divergence occurs with mutations in one gene copy leading to different clusters binding to different transcription factors during different stages of pre- and post-natal development.

for example:
zeta and epsilon expression decreases to zero after 6 foetal week.
beta globin expression increases after 6 foetal weeks and maintains a high plateau from 12 foetal weeks onwards during foetal and postnatal development.
alpha globin increases prenatally and then maintains a constant high level (higher than beta) pre and postnatally. gamma.
gamma globin increases to peak at 20 foetal weeks and then declines to zero by post-natal 24 weeks.

Question 19

what is a pseudogene?

Answer 19

a pseudogene is a non-functional segment of DNA that structurally looks like a functional gene

occurs due to gene duplication where one cope carries out the original gene function and the other copy diverges through changes in its coding sequence - in this case, the changes render the gene non-functional.