Populations And Evolution Flashcards

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1
Q

Define gene pool

A

All the alleles of all the genes of all the individuals in a population at a given time / all the alleles in a population

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2
Q

Define allelic frequency

A

The number of times an allele occurs within a gene pool

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3
Q

What is the hardy weinberg principle

A

P squared + 2pq+ q squared = 1 (genotype frequency). Where p squared is homozygous dominant, q squared is homozygous recessive and 2pq is heterozygous. P +q=1 (allele frequency). Start with q squared (convert % in decimal) then square root to find q, find p by 1-q then find 2pq by 2xpxq

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4
Q

What are the assumptions for the hardy Weinberg principle to work

A

Proportion of dominant and recessive alleles remains same from one gen to next. Only happens if: no mutation, population is isolated so no gene flow in or out, population is large, mating in pop is random and no selection (alleles equally likely to be passed on). Allele freqs can change due to natural selection so hardy wenberh doesn’t apply

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5
Q

Examples when a new allele leads to increased reproductive success

A

Sickle cell allele more prevalent in areas with malaria as presence of allele is more resistant to malaria and having do dominant version means. There is enough healthy red blood cells to live normally

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6
Q

Define phenotypic variation

A

The difference in phenotypes between organisms of the same species

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7
Q

How can environment affect variation

A

Can affect phenotypes e.g sunlight hours, supply of nutrients, availability of water, temp range, 02 levels (abiotic factors affect growth). Example: plant with tall genes may never grow tall if lacking nutrients

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8
Q

Sources of genetic variation

A

1.Mutation is the primary source, 2. random fertilisation of gametes and 3. crossing over, independent assortment/segregation of homologous chromosomes in meiosis

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9
Q

What is genetic drift

A

The change in composition of a gene pool (allele and phenotype frequencies) as a result of chance or random events. Occurs faster and more significant in smaller populations, chance events have bigger impact on gene. Pool. Large less affected and maintain more stable allele frequencies. May result in loss of some alleles (including beneficial) and fixation/rise to 100% of others

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10
Q

Define evolution

A

Changes in allele frequency over time. Can be small scale/micro or large scale/macro (geological time and arise of new species)

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11
Q

What enables natural selection to occur

A

Genetic diversity is a factor enabling natural selection to occur. Genetic variation that exists within a population is heritable (genetic) and determined by presence of alleles

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12
Q

What are examples of selection pressures and what do they lead to

A

Predation, disease, intraspecific (competition between different species) competition and interspecific competition (within a species). Lead to differential survival and reproduction. Adaptations lead to differential reproduction in a species, allowing natural selection to occur

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13
Q

What are the principles of natural selection

A

Genetic variation exists within a population, new alleles arise by mutation. Environmental pressures lead to differential reproductive success in those with advantageous allele (more likely to survive and reproduce, passing alleles onto offspring). Over time, advantageous allele increases in frequency in population

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14
Q

How to find the actual frequency of an allele without hardy Weinberg

A

Number of alleles there are divided by the total number of alleles

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15
Q

Describe stabilising selection

A

An intermediate phenotype is favoured at the expense of extremes. Mean, median and mode stay the same but S.d. Decreases. Occurs when environmental conditions are stable. Extremes are selected against and allele freq of intermediate rise (e.g human birth weights)

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16
Q

Describe directional selection

A

When one phenotypic extreme is selected at the cost of the other. Shift in mean, median and mode. Happens in response to changes in the environmental conditions e.g. antibiotic resistance. Alleles for one extreme in increases as other decreases

17
Q

Describe disruptive selection

A

Natural selection maintains high frequencies of 2 different sets of alleles. Those with intermediate phenotypes selected against. Causes polymorphism (existence of 2 distinct phenotypes in a species. Happened in an environment that shows variation and shows bimodal distribution (2 camel hump shaped graph)

18
Q

How are new species formed

A

Via allopatric or sympatric speciation: the formation of a new species via isolation of the genetic pool from an existing species (prevents gene flow)

19
Q

Differences between sympatric and allopatric speciation

A

Allo: physical separation of a population, populations occupy different geographical areas sympatric: involves reproductive or behavioural separation, populations occupy same geographical areas

20
Q

The process of sympatric speciation

A

1.The process/speciation happened in the same environment/ state sympatric speciation has occurred 2.The change in x (flowering time/ behaviour..) arose through a chance mutation 3. The change in x lead to reproductive isolation so there was no gene flow between the two groups 4.Over time, variation occurred in the two populations due to mutations and Different alleles were selected and the allele frequencies of the 2 groups changed. 5.Eventually the two populations diverged so much/ became so different that they could not interbreed and produce fertile offspring, becoming 2 separate species . 6. This is an example of disruptive selection.

21
Q

The process of allopatric speciation

A

1The x were geographically isolated / allopatric speciation occurred. 2.The two populations became reproductively isolated so there was no gene flow between them. 3.The two populations were exposed to different selection pressures due to different environments/abiotic conditions. 4.Over time, variation occurred in the two populations due to mutations.
Different alleles were selected and their frequencies changed in the two populations. 5Eventually the two populations diverged so much that they could not interbreed and produce fertile offspring., becoming separate species 6. Example of disruptive selection

22
Q

How polyploidy results in sympatric speciation

A

Caused as a result of meiosis failure during gamete formation. If cells fail to undergo cytokinesis, chromosome no. Doubles in gamete (becomes diploid). Means offspring have additional sets of chromosomes (polyploidy). Speciation happens if offspring interbreed but cannot with original population