genetic drift stimulation

trends in genetic drift data

smaller populations fix alleles fasters with pop 5 being 100% fixed by gen 36

larger populations show slower or resist fixation within 80 generations due to more allele buffering so variation maintained over generations

fixation increase over time with generations but at a slower rate for larger populations

accuracy

how close a measurement is to the true value

miscount number of fixed generations or stopping at the wrong generation

fixed by stopping and recording exactly at each generation

validity

extent to which an experiment measures what it is designed to measure

computer randomness may not fully mimic biological randomness or processes and does not account for other real life factors like mutations or migrations

to improve choose a simulation that allows for mutation, migration and selection pressures to be included to better reflect how populations evolve

reliability

extent to which an experiment measures what its designed to measure consistently

limited number of colonies (10) may not show full range of outcomes and rather reflect an abnormality

repeat entire sim several times and take average to reduce impact of random outliers and increase the number of colonies

selection pressures definition

environmental factors that influence survival and reproductive success of organisms. favour certain phenotypes over others leading to changes in allele frequency within a population over time

reduce variation making population more susceptible to extinction or limiting adaptive potential.

in small population genetic drift can override natural selection

selection pressures

density dependent factors: predator, availability of resources, nutrient supply, disease

density independent factors: abiotic factors like temp, c02 levels

density dependent - how the growth rate of a population is affected by its own density

natural selection

non random selection of random variation that arises from mutations.

occurs when factors in environment confer a selective advantage on specific phenotypes to enhance survival/ reproduction as it changes allele frequency over time

charles darwin 3 observations of natural selection

1. variation: all members of a species vary. these variations were passed on from one generation to the next

2. birth rate: all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase leading to overcrowding and competition

3. natures balance: although birth rate of organisms was very high, each species number tended to remain at a relatively constant level

vocsic sample answer

variation in the presence of — would have existed in the population. there would have been a struggle for existence in —- due to more offspring being produced that can survive to maturity. those with —- would have been able to —- and would have survived selection pressures and reproduce due to survival of the fittest, passing on alleles for — to offspring. those without —- would’ve died or failed to reproduce so over time the population would’ve become more alike

genetic drift

random change in allele frequencies within a populations gene pool overtime due to chance events. non selective mechanism of evolution and doesnt depend on alleles advantage or disadvantage. fixation means allele reaches 100%

more significant in small populations beause each individual allele make up a larger population of gene pool and can lead to loss or fixation of alleles over time. in large pop allele frequencies change more slowly as random fluctuations have less impact

founder effect

type of genetic drift that occurs when a small group of individuals become isolated from a larger population and form a new population. may have reduced genetic variation and a gene pool not representative of original population

bottleneck effect

form of genetic drift that happens when a large population suddenly reduces in size due to a catastrophic event. surviving population has reduced genetic variation and may not represent original gene pool

gene flow

movement of alleles from one population to another through processes like migration or interbreeding. between adjoining groups the amount of genetic exchange can increase so populations become more genetically similar as alleles mix or decrease or stop which means populations diverge genetically and may eventually lead to speciation

allele frequency

proportion of specific allele among all alleles for a gene in a population

speciation

evolutionary process in which there is a formation of new species due to genetic divergence. often thru isolation or selection pressures

species

breeds that produce fertile offspring

principal of evolution

variation: there is variation of characteristics within a species

overpopulation: more offspring of a species are produced than can possibly survive to maturity

competition: there is a struggle for existence or competition for survival - some will not survive to reproduce

survival of the best fit: individuals with characteristics best suited to that environment have more chance of surviving and reproducing due to selection pressures

inheritance: favourable characteristics are passed onto the next generation

change in allele frequency: in the gene pool the proportion of alleles that produce favourable characteristics gradually increase

heterozygous advantage sample answer

1. heterozygous individuals for —- have survival advantage

2. in populations where —- is present

3. homozygous individuals for —- will likely die of —-

4. homozygous normal individuals will likely die of —-

5. heterozygous individuals are more likely to survive to reproduce ensuring allele remains in the gene pool

sickle cell anaemia

single gene mutation that gives red blood cells an abnormal shape which gives resistance to malaria as it is caused by an endoparasite which reproduces inside rbc

in areas with common malaria there is higher incidence of people who are heterozygous. these invididuals produce enough normal blood cells to avoid the more severe affects associated with sca but also produce enough sc to confer an increased resistance to the malarial parasite.

a condition where both alleles are beneficial is known as heterozygous advantage

barriers

geographical - river, mountain, lake canyon

reproductive - mating patterns

temporal barriers (time) nocturanl, seasons

anatomical barrier - sex organs are incompatable

physiological - sperm and egg incomptabilbe

title

Effect of Population Size on the Number of Colonies /10  with Fixed  alleles Over Generations in a Genetic Drift Simulation

aim

to investigate how population size affects the rate and extent of allele fixation due to genetic drift over multiple generations

hypothesis

smaller populations will experience faster and more frequent allele fixations over generations due to stronger effects of genetic drift, whereas larger populations will retain genetic variation for longer

method

used a computer simulation of genetic drift based on drosophilia eye colour with bw allele

fixed 5 population sizes 5, 10, 20, 40, 80

ran 10 colonies for each population size

recorded number of colonies where the allele was fixed 0/100% at generations 10, 20, 40, 80

simulation set to stop when fixed

support for hypothesis

yes the data supports the hypothesis as alleles fixed faster and more frequently in smaller populations due to stronger genetic drift

fixation

100% of individuals in the population have the same allele meaning there is no variation left at that gene locus

conclusion

this simulation demonstrates that genetic drift causes alleles to become fixed more rapidly in smaller populations. as population size increasees, the impact of random events on allele frequencies decreases, making fixation less likely within the same number of generations. the data supports the hypothesis and aligns with biological theory. limitations in validity, reliability and accuracy should be addressed in future simulations through increased colony numbers, strict timing control and inclusion of other evolutionary forces