topic 8 : origins of genetic variaiton Flashcards
what are the sources of new genetic variation
- mutations
- crossing over (metaphase/anaphase 1)
- independant assortment (metaphase/anaphase 1 & 2)
- random fertilisation
what is an allele
an alternative form of a gene
what does it mean if an allele is dominant
an allele that is always expressed the phenotype, even if only one of them is present (heterozygous) - present in homoxygous and heterozygous
what does it mean if an allele is recessive
an allele that is only expressed in the phenotype if two copies are present (homozygous) or if there is only one of the allele
what does phenotype mean
the observable characteristics of an organism
what does genotype mean
all the alleles present in a cell of an organism
what does codominance mean
both of the alleles contribute to the phenotype without mixing
what are multiple alleles
more than 2 possible versions of an allele
what are chi squared tests used for
used when both variables are categorical (eg. height gourps at short/average/tall and gender male /female)
also normally used to check for autosomal gene linkage
what does autosomal gene linkage mean
when 2 genes on the same chromosome are linked and inherited as if they were the same gene (eg. brown eyes and brown hair), not sex-linked
what happens if the closer the 2 genes in autosomal link are located
then they are less likely to be separated during crossing over (the characteristic will be carried out)
what does sex linked mean
they are on the X chromosome (this is why some health conditions are more common in men because they don’t have two X chromosomes -> only need one copy for it to be expressed
what are two examples of sex linked conditions
haemophilia (absence of clotting factors)
red-green colourblindness
why do frequencies of alleles change over time?
this is due to natural selection, which drives evolution
why does natural selection occur
it occurs due to various seleciton pressures
what is natual selection
process through which population of living organisms change and adapt
what are the three types of natural selection
stabilizing, disruptive and directional
what is stabilising natural selection
conserves phenotypes already existing in the population and hence reduces variation. selection is agains the extreme (more of the average features)
what is disruptive natural selection
increased diversity in a population. common when conditions are varied and small sub population evolve different phenotypes based on these conditions. Selection is for extreme phenotype (completely opposite)
what is directonal natural selection
normal natural selection which shows change from one phenotype to another which happens to be more advantageous for the envrionment
what is a population bottle neck
a serious event that causes the population to reduce by at least 50% resulting in a dramtic change to the gene pool and allele frequencies and hence genetic diversity.
what is genetic bottle neck?
sharp reduction in the size of a population due to environmental catastrophes like earthquakes, floods or diseases or human destruction like habitat destruction, overhunting or genocide
what is the main difference between genetic bottlenecking and natural selection
genetic bottlenecking is like natural selection, but it happens much quicker and it is much more extreme
natural selection favours more advantageous characteristics and the population is bigger.
what happens if there is less genetic diversity in a population
they are less likely to survive when met with different diseases or environmental conditions
what is founder effect
loss of genetic variaitonw hen a small gorup of individuals are isolated and they form a new population- . they evolve n have allele frequencies tthat are not representative of the original pop.
what is genetic drift
the allele frequencies are changing due to chance and not be a specific selection pressure.
compare and contrast stabilising selection with disruptive selection
differences :
-n stabilising selection selects against the extreme phenotypes/disruptive selection selects against the mean/median phenotypes
- stabilising selection maintains 1 population/disruptive selection results in 2 distinct populations
similarities ;
- both change the frequency of alleles
- both select against phenotypes (reduces the variation)
In 1994, there were only 20 gilbert’s potoroo individuals, 12 of which were in a captive colony.
a captive breeding programme was set up using :
- four adult females and one young female
- one adult male, two young males and one young male sill in its mother’s pouch.
explain why allele frequencies may cause problems in this population of potoroos
- population size is small due to the genetic bottle/founders effect
- gene pool is very small/genetic variation is reduced
- there is an increased likelihood of interbreeding which can cause problems.
state what is meant by the term biodiversity
the variation of alleles in a gene pool
explain why, in 2016, the genetic biodiversity of the lynx population in the area where they had been reintroduced was much lower than in the protected area
- only a small number was reintroduced so there is more interbreeding
- casuing a limited gene pool
what are the conditions for the hardy weinberg equation
- no mutation
- random mating
- large population
- no migration (in or out))
- no selection pressure
