Evolution Flashcards
What was JP Lamarck’s theory for how evolution occured?
Desire incurred physical change - for example, a giraffe has a long neck because it’s short necked ancestors desired the fruits at the top of the tree, so the next generations had long necks.
What is evolution?
the genetic change in allele frequency over time in a population
what is the only consistent force that incurs evolution?
natural selection
what is the evidence for evolution?
- fossils
- imperfection in modern organisms
- molecular genetics
- being able to observe natural selection in action via timelapses of bacteria
what is an example of “bad design” as proof of evolution?
humans - left recurrent pharyngeal nerve
- distance from brain to larynx is only 30cm, but this nerve is 1m long, as it loops all the way around the aorta.
- this is due to the layrnx evolving from the brachial arch, and while the brachial arch changes over time with evolution, the nerve stays in the same place.
what is the correct word to describe the action of natural selection?
“tinkering”
what is convergent evolution?
distantly related species show similar adaptations due to similar selection pressures, but often with different underlying genetic factors.
what are some examples of animals NOT displaying convergent evolution?
- kangaroos hopping for locomotion
- elephants having a prehensile trunk
what are some examples of natural selection in action?
- lizards in a hurricance
- lizards before hurricane irma were measured, and after they were measured again. On average, it was discovered that the remaining lizards had longer arms, bigger toe pads, and shorter hind legs.
how do molecular genetics prove evolution?
- DNA is the sole universal carrier of the genetic code
- evolution can be reconstructed by showing the change in allele freq. in a species
- shows existence of a universal common ancestor
what is LUCA?
- Last Universal Common Ancestor
- all life can be traced back to LUCA
what is eukaryogenesis?
- a one time event, probably around two billion years ago
- (probably) archaebacterium engulfed a heterotrophic eubacterium, which eventually became mitochondria
what is speciation?
biological definition - a population of reproducing organisms that is isolated from other populations
what are the problems with the biological definition of speciation?
- doesn’t apply to organsims that can reproduce asexually
- doesn’t apply to extinct organisms (dinosaurs)
- difficult with bacteria that have horizontal gene transfer
what is allopatric speciation?
via physical isolation, one population of a species becomes a different species
what is stabilising selection?
selection acts against both extreme phenotypes and favours the intermediate - bell curve is thin and in the middle of the graph
what is disruptive selection?
two extreme phenotypes are selected for, whereas the intermediate is selected against - curve has peaks on far left and far right of graph and dip in the middle of the graph
what is directional selection?
when individuals with one specific phenotype on one side of the mean are selected for - curve is shifted to the far left or the far right
what is genetic drift?
the process by which random effects can cause major changes in small populations - e.g. in a small field of red and white flowers, by chance, only the red ones reproduce - leads to the next generation only having red flowers
- process can occur via a founder effect/ bottlenecking event where population is drastically reduced
in what environment does sympatric speciation occur?
when there are no physical barriers seperating a population, and all members are in close proximity to one another.
sympatric speciation seems to occur spontaneously
what are some genetic factors regarding speciation?
- requires a sampling effect (e.g. genetic drift or genetic bottlenecking event) combined with long periods of time
- essentialy random events
- speciation = branching process - 1 species can give rise to more than 2 others
what are some prezygotic barriers (barriers before mating) to prevent interbreeding?
PRE mating attempt
- habitat isolation - if two individuals are geographically isolated
- temporal isolation - timing of critical reproductive events prevents organisms from interbreeding
- behavioural isolation - courtship behaviour is different, which leads to no mating attempt occuring - negative rizz between species :(
POST mating attempt
- mechanical isolation - genitals are different shapes, and do not fit together, resulting in mating being impossible
- gametic isolation - egg and sperm both join together but no zygote is created due
what are some postzygotic barriers (barriers after mating) to prevent interbreeding?
-reduced hybrid viability - hybrids are produced but fail to develop to reproductive maturity
-reduced hybrid fertility - hybrids are produced but fail to produce functional games (hybrid is sterile)
- hybrid breakdown - F1 hybrids are fertile, but F2 hybrids fail to develop properly
what is Fitness?
the relative probability of survival + reproduction of a given genotype
i.e. capability of passing down your genome
what is Altruism?
when one organism benefits another, normally at their own expense
what is Hamilton’s Rule?
‘natural selection of genes that lead to social activity via the sharing of these genes between performer and recipient.’
altruism has a cost (c) to the performer
receiving altrusim has a benefit (B) to the recipient
R = degree of relatednes
RB > C
What are Transposons?
mobile genetic elements - sequences of DNA that can move in the genome
how are transposons agents of evolution and disease?
- movement of transposons can cause mutations
- any character that prevents transposition (e.g. methylation) are favoured to prevent mutation
what is horizontal gene transfer?
the movement of genetic information between organisms, e.g. the spread of antibiotic resistance in bacteria
what are some examples of mutations that we can use to track evolution?
SNP’s - single nucleotide polymorphisms
Indels - insertions and deletions
How are DNA sequences compared?
- sequences are aligned
- each row = 1 DNA sequence
- each coloumn = bases in alignment
- asterisk is drawn in the sequences match up
e.g.
A C A G A C - G A
A C A T A C A G A - asterisks are not drawn under coloumns where bases are not in alignment
what is population genetics?
study of changes in a gene pool of a population
what is a polymorphic gene locus?
- a gene that codes for more than one allele
- different alleles are called polymorphisms
what is the hardy-weinberg equation?
p^2 + 2pq + q^2 = 1
p^2 = genotype frequency of A1 homozygote (dominant allele)
2pq = genotype frequency of A1A2 heterozygote
q^2 = genotype frequency of A2 homozygote (recessive allele)
how do you calculate genotype frequency?
- determine population size (e.g. 100)
- determine number of individuals with desired genotype(e.g. 40 people with A1A1 genotype)
- divide no. of A1A1 individuals by no. of total population (40/100)
therefore genotype freq. = 0.4
how do you calculate allele frequency?
- determine total number of desired allele (A1 is in both p^2 and 2pq, so therefore its value is doubled (e.g. 2 X 40) AND you have to add the number of heterozygous individuals.
e.g. (2 X 40) + 50 - divide this value by the total number of alleles (population size X 2, as there are 2 alleles per individual in this example)
therefore final equation is ((2 X 40) + 50) / 200
what is assortative mating?
individuals mating preferentially with unrelated partners of similar phenotype (e.g. tall men + tall women mating)
- positive assortative mating decreases heterozygosity and increases homozygosity (only for genes affecting phenotype)
- negative assortative mating will have opposite effect
how can fitness (w) be measured?
- a genotypes relative reproductive success
- e.g. if A1A1 has 8 offspring, WA1A1 = 1
- if A1A2 has 4 offspring, WA1A2 = 0.5
- if A2A2 has 2 offspring, WA2A2 = 0.25
