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a level biology > 3.7 genetics populations evolution and ecosystems > Flashcards

3.7 genetics populations evolution and ecosystems Flashcards

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1
Q

what is meant by species?

A

organisms that can breed to produce living, fertile offspring

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2
Q

what is meant by population?

A

group of organisms of the same species in a given area at a particular time and can potentially interbreed

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3
Q

what is meant by community?

A

a variety of species interacting in a common locations

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4
Q

what is meant by gene pool?

A

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

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5
Q

what is meant by allele frequency?

A

the frequency of a particular allele within the gene pool

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6
Q

what is meant by homozygous?

A

alleles of a particular gene are identical

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7
Q

what is meant by heterozygous?

A

alleles of a particular gene are different

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8
Q

what is meant by selection?

A

the process by which organisms that are better adapted to their environment tend to survive and breed at the expense of those less well adapted

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9
Q

what is meant by phenotypic variation?

A

genetic factors and environmental factors

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10
Q

what is meant by genetic variation?

A

meiosis, sexual reproduction, main factor - mutations

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11
Q

what is a normal distribution curve?

A

most traits are normally distributed, the most common result (mode) is near the average (mean) and the middle value (mode), when selection occurs the normal distribution curve may change shape

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12
Q

what is directional selection?

A

change in environment, changes in mean, extreme is selected for, e.g. antibiotic resistance

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13
Q

what is stabilising selection?

A

selection against both extremes, phenotypic variation decreases, environment has remained stable, e.g. birth weight

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14
Q

how do differences between the reproductive successes of individuals affect the allele frequency in populations?

A

there is a random mutation of alleles within the gene pool, if this allele is advantageous in the specific environment then the individuals with this mutation are better adapted. These individuals can grow rapidly and live longer compared to individuals with other alleles. This means they can reproduce and pass on this allele so the offspring also survive and reproduce better. The advantageous allele increases at the expense of the individuals with the less advantageous allele, change in the allele frequencies (evolution) in a population occurs.

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15
Q

what are selection pressures?

A

environmental factors that limit the population of a species, determine the frequency of all the alleles in the gene pool, vary from time to time and place to place, but every organism is subject to selection so certain factors may increase the chance of selection occurring

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16
Q

what are the examples of selection pressures?

A

predation, natural disaster, competition, disease

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17
Q

what are the selection pressures for stabilising selection?

A

selection pressure against both extremes, mean stays the same

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18
Q

what are the selection pressures for directional selection?

A

selection pressure for an extreme, mean changes

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19
Q

what is exponential growth?

A

the rate increases in proportion to the growing total number or size

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20
Q

evolution only occurs by natural selection if…

A

organisms reproduce, have sufficient resources, genetic variation within the population is present, phenotypic variation within a population is present, greater diversity = adapt to change

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21
Q

in order for populations to survive and increase exponentially they must…

A

have a suitable population size, minimise intraspecific competition, have a higher reproductive success

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22
Q

what factors make exponential growth unlikely?

A

high death rates from predation, low parental investment, lack of resources

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23
Q

why are death rates in a population not completely random/exponential growth unlikely to occur?

A

the organism will be better adapted to the environment i.e. camouflaged, suited to prevailing conditions i.e. catch food, resist disease

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24
Q

why is variation essential?

A

changing environments, new diseases, new predators, new competitions

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25
what is disruptive selection?
least common form of selection, opposite to stabilising selection, favours the extremes at the expense of the intermediate phenotypes,
26
when does disruptive selection occur?
when an environmental factor i.e. temperature takes two or more distinct forms summer=warm winter=cold
27
how is fur length an example of disruptive selection?
5 degrees in winter (long fur), 15 degrees in summer (short fur), results in two different species, each active in each season, one active in summer so only breed with others active in summer, producing short haired cubs, one active in winter only breed with others active in winter
28
why is disruptive selection important?
most important for causing evolutionary change, could result in two distinct species
29
how is coho salmon an example of disruptive selection?
large males and small males have a selective advantage, small males sneak up to females so reproduce and pass on their alleles, large males are fierce competitors so attract the females and reproduce passing on their alleles, intermediate sized is selected against as has no selective advantage
30
what is speciation?
the evolution of new species from existing species, enables evolutionary change and diversity due to reproductive isolation, genetic differences (mutations), geographical isolation, differences in two populations gene pools
31
which form of speciation is more common?
allopatric speciation
32
what is allopatric speciation?
a barrier occurs, preventing migration between populations, the environment of each new range may be different, different mutations occur in each range, different selection pressures, selection favours different advantageous characteristics, no gene flow/mixing of alleles can occur, changes in allele frequency, unable to interbreed even if barrier removed, adaptive radiation, takes millions of years
33
what is adaptive radiation?
the diversification of a species into forms adapted to different ecological niches
34
what is sympatric speciation?
less common than allopatric, same locations, reproductive isolation, breeding seasons or food preference
35
how is the apple maggot fly an example of sympatric speciation?
only lay eggs inside Hawthorns fruits (native to North America), apple trees introduced, some flies lay eggs in apples, mates are found by searching site where they were raised, raised in apples mate with flies raised in apples
36
how is seasonal breeding an example of sympatric speciation?
intermediate populations have no advantage
37
what is genetic drift?
genetic change due to chance, by chance fewer descendants of one phenotype are left behind
38
why does genetic drift occur in small populations?
a small variety of alleles (lower genetic diversity), not equal chance of each allele being passed on or if a mutation occurs, one allele/mutation is passed on very quickly, increase in allele frequency, speciation is more likely
39
what is the Hardy Weinberg principle?
a mathematical equation used to calculate the frequency of the alleles of a gene in a population, a statistical analysis, establishes the frequency of the dominant and recessive alleles and the frequency of heterozygous carriers in a population
40
what is the Hardy Weinberg equation?
p squared + 2pq + q squared =1
41
what does p squared represent?
number of individuals that are homozygous dominant (AA)
42
what does 2pq represent?
number of individuals that are heterozygous (aA or Aa)
43
what does q squared represent?
number of individuals that are homozygous recessive (aa)
44
what is the Hardy Weinberg principle based on?
the principle that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next
45
what are the key conditions for the Hardy Weinberg principle?
no new mutations, population is isolated, no selection bias, population studied is large
46
why must there be no new mutations for the Hardy Weinberg principle?
no introduction of new alleles
47
why must the population be isolated for the Hardy Weinberg principle?
movement encourages interbreeding reducing genetic difference
48
why must there be no selection bias for the Hardy Weinberg principle?
natural selection = advantageous alleles favoured
49
why must the population studied be large for the Hardy Weinberg principle?
prevents effects of random events effecting allele frequencies or changes due to chance
50
why must mating be random for the Hardy Weinberg principle?
prevents the selection of particular alleles
51
what is systematic sampling?
studies the distribution of a species
52
when is systematic sampling important?
gradual changes occur across a habitat, transitions within communities occur, zonation is present
53
what are the two types of transects?
belt transects and line transects
54
what is a line transect?
string or tape, organisms over which the line passes are recorded, usually using a quadrat
55
what is a belt transect?
strip of meter wide tape, second placed parallel to the first, species between the two belts are recorded
56
how would a scientist decide which type of transect to use in their investigation? (4 marks)
they would use a line transect if they needed to be quick also a line transect would be suitable if they were investigating the range of species. However a belt transect provides more data, tells you more about abundance and range, and shows distribution more clearly as there is more data.
57
what do transects show?
change in the number of species over a given area, not a comparison between two areas, used to show a trend
58
how do you use a transect?
1) place a transect (tape measure) down across a given area 2) place a quadrat down at equal intervals along the transect 3) carry out a second transect in a different part of the sample area but still close by your first sample 4) calculate a mean across the three transects studied 5) plot a graph and describe the pattern shown
59
describe how ecologists could have used quadrants and transects to obtain the data from which the graph was drawn?
first they would use a tape measure to produce a transect and then place quadrats down at equal intervals. they would count the number of seeds per square metre, they would then repeat the transect three or more times in different directions from the tree to calculate the mean
60
what is meant by abundance?
the number of individuals of a species in a given time, there are two main methods to measure the abundance
61
what are the two main methods used to measure the abundance?
frequency and percentage cover
62
what is frequency? (measuring abundance)
the likelihood of a particular species occurring in a quadrat
63
what is percentage cover? (measuring abundance)
estimate of the area within a quadrat that a particular plant species covers
64
how do you calculate percentage cover (measuring abundance)?
(number of squares species occurs/number of squares in total) x100
65
what are the positives to using frequency to measure abundance?
often expresses as a %, useful where a species is easier to count, a quick idea of the species present
66
what are the negatives to using frequency to measure abundance?
lacks information on the density, no detailed information distribution of a species, can be quite time consuming
67
what are the positives to using percentage cover to measure abundance?
useful when a species is abundant or difficult to count, data can be collected quickly, gives a representation of distribution identity
68
what are the negatives to using percentage cover to measure abundance?
less useful where organisms occur in overlapping layers, can be less precise, often subjective
69
what is mark, release, recapture?
a method used to measure the abundance of more motile species
70
what is the process of mark, release, recapture?
1) capture a sample of a species using an appropriate technique technique e.g. pitfall taps to capture ground insects, and count them 2) mark them in a harmless way e.g. by putting a pot of paint on them or removing a tuft of fur 3) release them back into their habitat 4) wait a week then take a second sample from the same population 5) count how many of the second sample are marked
71
how do you use mark release recapture to calculate population size?
(number caught inn first sample x number caught in second sample) / number marked in second sample
72
what assumptions must be made when using the mark release recapture method?
1) the marked sample has had enough time and opportunity to mix back in to the population 2) the marking hasn't affected the individuals chance of survival (by making them more visible to predators and the marking is still visible 3) there are no changes in population size due to births, deaths and migration during the period of the study
73
how do you take a random sample?
choose a small area within the area being investigated to sample, samples should be random to avoid sampling bias e.g. divide area into a grid and select coordinates using a random number generator, use an appropriate technique to take a sample of the population, repeat to reduce likelihood of results due to chance, estimate the number of individuals in the whole area by taking the mean of data collected in each sample and multiplying it by the size of the whole area
74
what are quadrats and transects used for?
investigating non-motile organisms (ones that don't move about e.g. plants) and slow moving organisms e.g. limpets
75
what are quadrats?
a quadrat is a square frame usually divided into a grid of 100 smaller squares by string, placed on the ground at different points within the area being investigated, the species frequency (how often a species is found) or the number of individuals of each species is recorded in each quadrat, the percentage cover can also be measured by counting how much of the quadrat is covered by the species, counting squares more than half covered, this is a quick way to investigate populations and you don't have to count all the individual organisms

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