Molecular Evolution Flashcards
What are the predictions that were made by Darwin’s Theory of Evolution by Natural Selection?
Evolutionary theory says tat man and apes descend from a common ancestor. Therefore intermediate forms must be present in the fossil record.
The theory of natural selection predicts that:
-Spontaneous natural variation occurs.
-These variations are stably inherited.
In natural selection, how does variation occur?
- mutations, due to changes in DNA sequence.
- mostly mistakes during DNA synthesis.
- rare because DNA synthesis is exceedingly accurate.
- most mutations are neutral or deleterious, a minority are beneficial.
In natural selection, how is selection involved?
- Observation of nature and the science of ecology that tells us that individuals are in competition with:
- predators
- prey
- members of their own species (intraspecific)
- new alleles may increase or decrease reproductive success.
What is relative fitness?
The average number of surviving progeny of a genotype (compared with competing genotypes) after one generation.
- if w<1, the frequency of the allele will decrease with each generation, untill the allele disappears (negative selection).
- if w>1, the frequency of the allele will increase with each generation, untill the allele reaches fixation (positive selection).
- fitness: how many offsprings will pass on your genes.
What are the small mutations that are possible?
- Base substituting
- Small insertion (causes frame-shifts, unless a multiple of 3 bases)
- Small deletion (causes frame-shifts, unless a multiple of 3 bases).
What are the large mutations that are possible?
- Large DNA duplications
- Large deletions
- Insertion of transposable elements=stuff in the genome that moves around- sequences can come out of one site and go into another site and cause a mutation.
- Viral insertions-retroviruses
- Chromosomes rearrangement- mutations on a very large scale.
How can molecular phylogeny be used?
- DNA mutations accumulate over time, so species that share a recent common ancestor will have fewer differences than species that are more distantly related.
- Sequence data can be used to generate evolutionary family trees.
- Medical implications: substances produced by fungi, which are toxic to bacteria, but not fungi, are called antibiotics.
What is an example of using molecular phylogeny to prove the theory of evolution?
-Suggested that HIV was introduced into the human population through a contaminated batch of polio vaccine.
-Some early types of polio vaccine were produced by growing polio virus on cultured monkey cells, which could have been contaminated by SIV.
What does molecular phylogeny tell us?
-Compared gene sequences from different strains of HIV, and from isolates of SIV from chimpanzees in different parts of Africa.
If you compare the molecular phylogeny of two species, why is it that consistently there is more differences (per unit of length of DNA), in intron sequences that in exon sequences?
-change in coding sequence is very likely to change the amino acid sequence -> non-functional protein, so the organism will either die or be less able to pass that on (less fit – negative selection will remove many of the mutations from the genome).
If you compare the molecular phylogeny of two species, why is it when you look at the coding sequences, there are more differences looking at every third nucleotide, compared to two?
-Wobbly 3rd base -> genetic code is redundant because more codons than there are AA, so several amino acids are coded for by more than 1 codon. When there’s more than 1 codon coding, the first 2 bases in the codon are specific, but the 3rd is optional because there’s some wobble when the tRNA binds to the codon -> changes in first 2 bases may change the amino acid but often a change in the 3rd base won’t change the amino acid. -Changing the amino acid -> sometimes codes for same a.a. but often not -> there’s strong NEGATIVE selection for changes in 1 st / 2 nd base of a codon, but much weaker selection for changes in 3rd base of the codon (because most often it won’t change the a.a sequence).
What is synonymous substitution?
Something that doesn’t change AA coded for by the codon.
What is non-synonymous substitution?
Changes the amino acid coded for.
LOOK AT NOTES TO SEE THE TABLE
LOOK AT NOTES TO SEE THE TABLE
How can gene duplication be involved in evolution?
- Gene duplication is a major driving force of evolution.
- Once a gene has been duplicated
- One copy can continue to maintain the original function
- While the other can evolve new functions.
- There are likely to be changes both in the coding sequence (i.e. in amino acid sequence) and in control sequences (so gene may be expressed in a different cell/ at a different time/ in response to something else).
Explain how hemoglobin is involved in evolution?
- Haemoglobins (Hb) are ancient in evolution.
- Duplication of an ancestral gene gave rise to myoglobin and haemoglobin.
- LOOK AT NOTES IN THE TABLE
- The ancestral globin gene has undergone multiple duplications and modifications to give rise to the α-globin gene complex on human chromosome 16, and the β-globin gene complex (chrom.11).
