Population Genetics Flashcards
(19 cards)
What is the gene pool
The sum total total of all genes and alleles in a population at a particular time
That is the genome
Refers to all DNA in an individual- the entire genetic complement in any organism
What are the assumptions that ensure Hardy-Weinberg equilibrium
- Large Population- less risk of random changes that would skew the distribution of alleles and genotype frequencies.
- Mating is random- there is an equal chance of any individual of any genotype mating with an individual of the same/ different genotype
- No mutations
- No migration/ emigration- population is isolated and there is no genes exchanged with other gene pools
- Differential selection is not occuring- no particular allele is at an advantage, therefore not more likely to survive and reproduce than others- all genotypes are equally favoured.
- Individuals are diploid- traits are inherited in typical Mendelian pattern
How is meiosis a source of variation
- Independent assortment- only one chromosome from each homologous pair enters a gamete- this depends on how they line up at the equator at the start of metaphase1- random and independent
- Crossing over- occurs at prophase1- facilitates the exchange of genetic material between homologous chromosomes- produce entirely new allelic combinations that werent present in either parental chromosome
- Cross fertilisation- male produce very large numbers of gametes, each with different chromosome and allele arrangements- females are more frugal with egg production as eggs are larger and require more investment- female only provides support and nourishment for a small number
-fusion of male and female gametes is entirely random
-mixes up allelic combinations but doesn’t produce genetic novelty- no new alleles produced
What is a mutation
A permanent change to DNA
What is base deletion
-When one base is removed from the sequence- results in a frameshift of the entire code beyond mutation- FRAMESHIFT MUTATION- significant consequence
-affects the rest of the base sequence and all following amino acids
-stop codon can be produced earlier in the sequence- results in a non functional protein produced
What is base substitiution
-When a base is replaced by another
-consequence is limited to one amino acid
-if the substitiution occurs in the third base, it may have no effect due to the degenerate nature-mutation described as neutral
-eg sickle cell anaemia
What is a chromosome mutation
-involve changes to large sections of DNA containing several genes or whole chromosomes
-large sections of chromosomes can break off during cell division and attach to another chromosome or get lost
-eg down syndrome
-turners syndrome
What is selection
The editing of genetically inheritable features, increasing the frequency of some whikst decreasing the frequency of others overtime
What is fitness
Descrribes how well an organism is adapted to its environment
What is a stabilising selection
-show a normal distribution, eg human height and weight
-average phenotypes are best adapted- more likely to survive and pass on genes to offspring
-extremes are less adapted and will be selected against
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What is directional selection
-average individuals are not the most adapted
-best adapted individuals have phenotypes that lie closer to or at one extreme
-most likely taking place if the environment is changing or a population or species colonises a new area
What is polymorphism
the presence of two or more genotypes, the rarest of which exceeds 1%, eg human blood groups or eye colour
What is a species
A group of organisms which are actively or potentiall capable of interbreeding to produce fertile offspring
What is speciation
The formation of a new species that are reproductively isolated from each other- unable to interbreed
What are the processes to speciation
- Original species becomes separated into two or more populations that become reproductively isolated from each other- breeding restricted to within the population
- Different forms of directional selection occurs in each isolated population, that results in the population becoming so different that they remain reproductively isolated even if they come into contact
-The initial isolation is usually geographical
-after separation, genetic divergence will occur between populations- different environmental conditions will encourage natural selection to act in different ways in the isolated areas
-in time, because of directional selection and genetic divergence- reproductive isolating mechanisms will develop that prevent interbreeding and gene exchange should the isolated populations overlap.
What are reproductive isolating mechanisms that can occur
-Barriers to the reproductive process- including mechanical barriers to mating and fertilisation, offspring fertility and reproductive cycles no longer synchronised
-Behavioural isolation- organisms have different behaviour patterns
-Ecological isolation- eg different habitat or food preferences, organisms breed at different times of the year
What is allopatric speciation
When two populations become geographically isolated- occurs when some of the population migrates due to geography changes- earthquakes
PPQ- Describe concisely the process of allopatric speciation
-The populations are isolated by geographical isolation mechanisms.
-This prevents interbreeding between the two groups
-Different selection pressures are experienced which allows the accumulation of genetic differences
