3 - Evolutionary genetics Flashcards
Darwin’s model of inheritance
increased use and disuse of parts ‘strengthened and enlarged certain parts, and disuse diminished them; and that such modifications are inherited’
Darwins model of inheritance
- ‘Gemmules’ - hypothesised organic particles containing heritable information
- distributed throughout the body carrying information specific to body parts
- before reproduction, gemmules combine to form complete sets of information
- modified gemmules inherited by offspring if environment changes parental traits
what’s the weissman barrier
- lamarckian inheritance not invalidated by Darwin, but by August Weissman
- he proposed only information in germ cells (e.g. gametes) is inherited
- changes to other cells (somatic cells) not passed on
- experiment removing tails of generations of mice
blending inheritance
dominant model in 19th century Europe, traits blend when inherited
- organisms appear to resemble a blend of parents characteristics
- not comparable with natural selection as variation would be lost
mendelian inheritance
- mendels pea experiments
- suggest inheritance is particulate
- offspring inherit two alleles of their traits
- these traits are recessive or dominant
give an example of mendelian inheritance in humans
e.g. ABO blood types and cystic fibrosis.
- (most human traits are not caused by single genes)
- most human traits are polygenic - so lots of variation and continuous
DNA
molecule containing heritable information in all cells in the body
-stored in a code of 4 types of nucleotides
- genes and environments interact to build an organism
gene
basic unit of heritable information: DNA sequence, may code for proteins/ RNA
- a genome: organisms DNA sequence
- organised into chromosomes (23 pairs in humans)
- most species diploid: 2 copies of genome in somatic cells
genotype vs phenotype example
albinism
where does variation come from
- mutation - genetic variation
- recombination - creates new combinations of existing genes
- mitosis (division of somatic cells - not inherited) (mutations can also cause cancer) and meiosis (division of germ cells - changes inherited)
is mutation random
rate varies, but mutations are random in relation to fitness, not more likely when organism ‘needs’ them.
mostly neutral or negative effects
epigenetics
environmental variation results in differences in gene expression, affects if how and when genes are switched ‘on’ and ‘off’.
reversible and does not change actual DNA sequence
epigenetic study
- high care and low care mice,
- possibly intergenerational trauma in humans
was Lamarck right?
no:
- epigenetic changes not from use and disuse
- epigenetic changes reversable
- genetic transmission more stable
- few well sustained case studies in humans
yes:
- it is not a Neo-lamarckian model of evolution
- does not mean you can alter your own DNA
CITE: Haig (2006)
do we need an ‘extended synthesis’
read up on this!
yes - Kevin Lala
no - Wray, Hoekstra et al
micro vs macroevolution
microevolution - small temporal and spatial scales, changes within species
macroevolution - large temporal and spatial scales, changes at species level
is evolution gradual?
READ UP! + some studies
phyletic gradualism vs punctuated equilibria
from micro to macro-evolution
- rates + patterns of evolution vary across time and between lineages
- variation in rates at macro-scale driven by micro-scale processes
- variation in mutation rate and natural selection strength
- can use phylogenetic comparative methods to test these hypothesis
