defintions Flashcards
population genetics
a field in biology which aims to investigate genetic differences within and between populations. This is key to modelling and studying evolution. evolution used to be studied using fossils, however these are not good for studyting invertebrates and plants
theory
a widely accepted set of principles that have been devised based on observations and expactations
population
a group of randomly mating individuals of the same species, in an area.
natural selection
the idea that lots of intraspecies variation exists due to random DNA mutation, and more organisms are born than can survive. those with phenotypes which help them gain food, fend off predators or aboid stress are selected by the environment to pass on their genes
Charles Darwin and Russel Wallace
involves observing something, predicting something, experimentation and then testing the results statistically to see if the observed results support the prediction.
may involve measurments of DNA, morphology etc
the organisms which are studied are usually yeast or drosophila, arabisopsis
variation
a difference in a trait between two entitys
qualitative/discrete; a trait which falls into discrete catagories; flower colour, sex etc. usually controlled by a single gene/a few genes
quantitative/continuous; a trait which doesn’t fall into discrete categories and has a wide range of possible values. these traits are controleld by many traits and the environment.
when plotted graphically, the trait follows normal distribution
gene
a sequence of DNA which is expressed as a polypeptide
allele
a variant form of a gene which has arose through mutation wild type(+) is the most common homozygote/heterozygote
locus
the position of a gene on a chromosome
genotype
an organisms combination of alleles
Aa, 12, AB, A1 A2
hardy Weinberg principle
things that can deviation fro Hardy-Weinberg equilibrium
an equilibrium which is checked for. if the equilibrium is not present then this means selective forces are acting on the population
inbreeding; mating between closely related individuals or selfing of plants
surplus of homozygote
population structure; metapopulation is divided into subpopulations. this occurs when the migration force which mixes populations is less than the force which is diversifying populations
suprlus of homozygotes
non random mating
a)assortative mating (positive assortative mating); similar organisms mate more than would be expected. tall humans and other tall humans
homozygous suprlus
b)dissasortative mating (negative assortative mating); non similar individuals mate more than would be expected.
animals with different immune systems
defecit of homozygotes
selection against a genotype; if theres ever a defit of a genotype, one possible explanation is selection against that genotype. very vague; use other explanations if possible
hybridisation; closely related species produce an offspring; homozygous surplus
discuss processes which determine genetic variation in populations
1) mutation; increases diversity; very weak force
- many generations needed for mutation to become prominent
- 90% are disadvantageous, 1% advantageous
- easily lost by drift
2) migration; increases diversity; strong force
- only a few individuals need to migrate to prevent difference accumualting between populations
3)natural selection; decreases diversity
4) genetic drift; decreases diversity; random undirected changes in allele frequency which occur from generation to generation; strongish force in small populations
fixation/loss of allele
biston betularia
peppered moth whos colour is determined by a single gene
additive
the fitness of a heterozygote falls inn between the fitness of the homozygotes
overdominance
aka; heterozygote advantage
the heterozygote has a higher relative fitness than both homozygotes
how is genetic variance in a population measured
work out the expected heterozygosity
if there are only 2 alleles then just work out 2pq
if theres more than two alleles then do 1-p^2-q^2-r^2
discuss different levels of heterozygosity
individual heterozygosity of a single locus in a subpopulation; Hi
expected heterozygosity in a subpopulation Hs
expected heterozygosity in a total population Ht
when theres no HWE in place, what happens to the expected heterozygosity (He) and the observed heterozygosity
they’re different
discuss wrights F statistic
measure of population structure
- 0= extremely different populations
- 2= moderately different populations (scale isint linear)
- 0=identical populations
microsatellite markers
highly repetitive DNA such as tandem repeats (TATATATATA) which vary from species to species so can be used to study how genetically similar organisms are and their evlutionary history.
these are non fucntional sequences of DNA so mutate very frequentlyand have no selection pressure
gene analyser
a machine with many gel electrophoresis gels. it is used to analyse multiple samples, for example multiple samples of PCR’d microsatellite markers
british red squirrels
ancestry was investigated using single squirrel hairs from hancock museum;
british squirrel mDNA reveaked that infact most british squirrels have european ancestryl swedish halotype appeared in 1960’s
squirrel microsatellites were investigated to look at genetic variaiton between sub populations:
squirrels can travel up to 1.5km
british population is fragmented into subpopulations
squirrels can use keilder forest as a biological coridoor between cumbria and scotland
things that effect the amount of genetic variation in a population
mating system used
mobility of species
presence of fragmentation
why are some populations small
why do these populations have low levels of variation
what are the effects of having low genetic variation
limited resources
founder effects
bottleneck
strong effect of genetic drift
inbreeding depression; related individuals breed and have offspring which are less fit; cheetah bottleneck in 1969 and declining diversity ever since; they now have structural abnormalities and unusual shaped sperm
inability to adapt to changing environments such as presence of disease
inability to evolve
northern seal population once went down to a few hundred; the populaiton is now stable at 10,000 but there are concerns it wouldnt survive if a new disease emerged
founder effect
when a small number of individuals start a population
- genetic drift strong
- new population has different allele frequencies to aprent population; rare alleles for example. dversification occurs
- amish population was started by 200 german immigrants; dwarfism genes leading to polydactyl an short stature
bottleneck
a sudden dramatic reduction in population size
regular events like seasonal variaition
irregular events like disease
pressure such as humans destroying habitats
metapopulation
when a group of species exists in a number of smaller popualtions isolated from eachther because the species doesnt like to swell in the intermediate space
- mountain sheep only exist at high quality patches of land, and the use the land between to move about
- ponds in the middle of a habitat
- mountains in the middle of a desert
- within subpopulations there are low levels of variation, but the metapopulation as a whole has large amounts of variation
haplodiploidy
males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid
eusociality
cooperative brood care, some individuals are non productive and aid rearing of others/are workers, parents and offspring have overlapping generations
parthogenesis
when males develop from unfertilised eggs
monogynous
polygynous
monogynous; having one reproductive female (one queen bee)
polygynous; having more than one reproductive female (multiple queen bees)
ant characteristics
eusocial (live i colonies with nonreproductive workers and a isngle queen)
haplodiploidy
plasticity
change in phenotype in response to environment. when a water buttercup is underwater the leaves change shape and become thinner
heritibility
the portion of variation which is inherited
0=all variation due to environment
1=all variation due to genes
broad sense heritability; how genetics effects phenotype
narrow sense heritability; how additive geneticsdetermines phenotypic differences
how can heratibility be measured
I) look at how selection effects phenotype; number of abdominal bristles on drosophila goes up if you select for high bristle number; must be genetic influence
ii) do regression between parent and offspring
iii) look at similarity of related individuals
ideal population
one with random mating, equal sec ratios, no selection, all members have equal contribution to the next generation
effecttive popualtion
the size of an ideal population
eusocial
solitary
eusocial; one queen to many drones
solitary; one male to one female
what is key to being defined as a population
random mating
