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
