Evolution and phylogeny

SL22018

3 domains of life

• bacteria

• archea

• eukarya

Non adaptive evolution

• genetic drift

• random mutations and random subsampling

• possibly advantageous, disadvantageous or neutral mutations

• despite advantageous chance may not select mutation so it goes extinct

• even a disadvantageou mutation might by chance be propagated

When was the origin of species published

1859

what 2 ideas did the origin present that were in conflict w the bible literalism

• the continuity of species- common ancestor, species going from one to another but not the process of it 

• evolution by natural selection- relationship between form and function

why wasnt the evolution by natural selection hypothesis accepted by 1900

• scientists didnt know how old the earth was and if it had enough time to evolve

• darwin emphasized artificial selection and how slow gradual effects can have major long term changes.

darwins estimate of how old the earth is

• darwin didnt know how old

• estimated with geologists for best guess

• 300 million years

thomsons estimate of age of earth

• knowing size and rate of heatloss from surface can calc age

• heat gradient known from mines- 50 feet deep = 1 degree hotter

• came up w estimate of around 20-40 million years

• he didnt know about radioactivity which threw off 

what is fishers fundamental theorem

rate of evolution = variance in fitness

why do cod mature faster and end up smaller

diesel engine powered fishing boats warming up water and fishing from the breeding grounds

jenkins objection to natural selection

• he theorised that blending inheritance was true and therefore no variation and no natural selection

• diluting beneficial trait and everyone ends up being the same

why does selection matter and inheritance dosent

because of mendelian inheritance

Types of selection

group selection- is the chance going to be good for the species

individual selection- is the change going to be goo dfor the individual

gene selection- is the change going to be good for the allele

RA fishers solution

1:! investment ratios are the stable solution from an individual point of view

even though the females put the most investment into next generation the males will have huge amount of offspring and therefore their genes get passed on

haplodiploid relationships

sisters are more related to eachother than they are to brothers

meiotic drive

genetic conflict

• non mendelian transmission of alleles to manipulate meiosis to be inherited more than 50%

• often costly to fitness

hamiltonian sex ratios

predictions based on local mate competition (males compete w brothers for mates favouring female based sex ratios)

heritability

proportion of total phenotypic variation of a continuous trait which is due to genetic variation

(if there is no variation in a trait then heritability has no meaning)

how can we measure heritability

• parent offspring regression

• using the difference between inbred lines derived from the same outbred stock

• twins (method of concordance and MZ’s separated at birth)

• selection experiments

parent offspring regression

estimates heritability by regressing offspring trait values on mid parent values, where the slope equals narrow sense heritabilitv

using inbred lines to estimate heritability

comparing trait variance within genetically identical lines (environmental) to variance between lines (genetic)

using twins to estimate heritability

comparing trait similarity in monozygotic versus dizygotic twins

heritability inferred from their difference in correlation

2 methods:

• condordance how much more similar are MZ twins to DZ twins

• MZ separated at birth

using selection experiments to estimate heritability

by measuring the response of a trait to artificial selection, using the breeders equation h2=R/S

polymorphism

when 2 or more alleles are present in a popn at appreciable frequencies

The problem of polymorphism

why genetic variation persists despite selection

• polymorphisms can be maintained by balancing selection, neutrality or mutation-selection balance making variation common overall but most alleles rare

the neutral theory of evolution

• proposes most evolutionary change at the molecular level is caused by genetic drift of selectively neutral mutations

• most molecular polymorphisms are neutral

• most fixed differences between species are neutral

• substitution rates are driven by mutation rate not popn size

• genetic drift dominates over selection for most molecular charges

problems with neutral theory

1. very little difference in polyorphism levels between species

2. neutral theory predicts a constant rate per generation time

3 theories for evolutionary change

• positive selection

• strict neutral evolution

• nearly-neutral evolution

non synonymous

changed gene and protein

synonymous

changed gene but not the protein

Ks

the number of synonymous subsitutions per synonymous site

ka

number of non synonymous substitutions per nonsynonymous site

how do you tell if a protein is neutrally evolving

Ka/Ks diagnoses whether mutations that change a protein are always neutral

dispersion index tests whether those mutations that are fixed are likely to spread by drift

orthologus genes

a gene found in different species that originated from the same ancestral gene through a speciation event, and typically retains the same or very similar function.

what is FOXP2?

A transcription factor involved in neural development and motor control (important for speech and language)

mutations in FOXP2 can cause speech and language disorders

what does FOXP2 tell us about language evolution

changes in FOXP2 likely contributed to speech motor learning, supporting the evolution of spoken language in humans