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Y13 Biology > 7. Populations, Evolution & Ecosystems > Flashcards

7. Populations, Evolution & Ecosystems Flashcards

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1
Q

What is meant by the term genotype?

A

Genetic constitution of an organism

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2
Q

What is meant by the term phenotype?

A

The expression of this genetic constitution (genotype) and it’s interaction with the environment

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3
Q

What are alleles and how do they arise?

A

Variations of a particular gene (same locus) —> arise by mutation (changes in DNA based on sequence)

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4
Q

How many alleles of a gene can be found in diploid organisms?

A

2 as diploid organisms have 2 sets of chromosome (found in homologous pairs)
- but there may be many alleles of a single gene in a population

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5
Q

Describe the different types of alleles

A

Dominant allele - always expressed (shown in the phenotype)
Recessive allele - only expressed when 2 copies are present (homozygous recessive)/NOT expressed when dominant allele present (heterozygous)
Codominant alleles - both alleles expressed/contribute to phenotype (if inherited together)

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6
Q

What is meant by the terms homozygous and heterozygous?

A

Homozygous - alleles at a specific locus (on each homologous chromosome) are the same
Heterozygous - alleles at a specific locus (on each homologous chromosome) are different

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7
Q

What do monohybrid and dihybrid crosses show?

A

Monohybrid cross - inheritance of one phenotypic characteristic coded for by a single gene
Dihybrid cross - inheritance of 2 phenotypic characteristics coded for by 2 different genes

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8
Q

How do you represent the alleles for blood type, same gene with different alleles?

A

As a capital letter to the power of another capital letter
I^A, I^B, I^O

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9
Q

What is the dominance for alleles for blood group?

A

IA and IB are codominant
IO is recessive to IA and IB

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10
Q

How do you determine the probability that the next child will be a certain sex with a disorder?

A

Find the probability of the having the disorder and then multiply by 0.5

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11
Q

Explain the evidence from a pedigree diagram which would show that the allele for x disease is dominant

A
  • diseased parents have a child without the disease
  • so both parents must be heterozygous/carriers of the recessive allele
  • if it were recessive, all offspring would have disease
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12
Q

Explain the evidence from a pedigree diagram which would show that the allele for disease x is recessive

A
  • Parents without disease have a child with disease
  • So both parents must be heterozygous/carriers of recessive allele
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13
Q

If 2 genes are on 2 different chromosomes and are not linked, what possible gamete combinations can occur?
e.g genotype AaBb

A

Gametes formed: AB, Ab, aB, ab

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14
Q

What is a sex-linked gene?

A

A gene with a locus on a sex-chromosome (normally X)

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15
Q

Explain why males are more likely to express a recessive X-linked allele

A
  • Females (XX) have 2 alleles —> only express recessive allele if homozygous recessive/can be carriers
  • Males (XY) have 1 allele (inherited from mother) —> recessive allele always expressed
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16
Q

Explain the evidence from a pedigree diagram which would show that the allele for Q disease on the X-chromosome is recessive

A
  • Mother without Q has a child with Q
  • So mother must be heterozygous/carrier of recessive allele
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17
Q

Explain the evidence from a pedigree diagram which would suggest that disease Q is caused by a gene on the X chromosome

A

Only males tend to have disease Q

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18
Q

Explain the evidence from a pedigree diagram which would show that the gene for disease Q is NOT on the X chromosome

A
  • Q father has daughter WITHOUT Q
  • Q father would pass on allele for Q in X chromosome of daughter, carrier of disease
  • Q mother has son WITHOUT Q
  • Q mother would pass on allele for Q on X chromosome so son would have disease Q
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19
Q

Explain how autosomal linkage affects inheritance of alleles

A
  • 2 genes located on the same autosome (non-sex chromosome)
  • So alleles on same chromosome inherited together
    > stay together during independent segregation of homologous chromosomes during meiosis
  • But crossing over between homologous chromosomes can create new combinations of alleles
    > if the genes are closer together on the autosome, they are less likely to be split by crossing over
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20
Q

In fruit flies, the genes for body colour and for wing development are not on the sex chromosomes. The allele for grey body colour, G, is dominant to the allele for black body colour, g. The alleles for long wings, L, is dominant to the alleles for short wings, l.
A cross was carried out between flies with grey bodies & long wings (heterozygous for both) and flies with black bodies & short wings.
The result of this cross was 225 offspring with a grey body & long wings and 220 with a black body & short wings. Explain these results

A
  • the 2 genes are linked/autosomal linkage
  • no crossing over occurs/genes are close together
  • so only GL and gl gametes produced
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21
Q

What is epistasis?

A

Interaction of (products of) non-linked genes where one masks/suppresses the expression of the other

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22
Q

Describe when a chi-squared test can be used

A
  • When determining if observed results are significantly different from expected results (frequencies)
    > e.g comparing the goodness of fit of observed phenotypic ratios with exprected ratios
  • Data is categorical (can be divided into groups, e.g phenotypes)
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23
Q

What is an autosome?

A

A non-sex chromosome

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24
Q

Suggest why in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios

A
  • Fertilisation of gametes is random
  • Autosomal linkage/epistasis/sex-linkage
  • Small sample size —> not representative of whole population
  • Some genotypes may be lethal (cause death)
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25
Q

Describe how a chi-squared value can be calculated

A

x^2 = (sum of) (O-E)^2 / E

O = frequencies observed
E = frequencies expected (multiply total n with each expected ratio as a fraction)

26
Q

Describe how a child-squared value can be analysed

A
  1. Number of degress of freedom = number of categories - 1
  2. Determine critical value at p = 0.05 from a table
    - if x^2 is greater than or equal to the critical value at p < 0.05, difference is significant so reject null hypothesis, so less than a 5% probability that difference is due to chance
    - if x^2 is less than critical value at p < 0.05, difference is not significant so accept null hypothesis, so there is more than a 5% probability that difference is due to chance
27
Q

What is a population?

A

A group of organisms of the same species in one area at one time that can interbreed

28
Q

What is a gene pool?

A

All the alleles of all the genes in a population at any one time

29
Q

What is allele frequency?

A

Proportion of an allele of a gene in a gene pool

30
Q

What does the Hardy-Weinberg principle state and what are the conditions under which the principle applies?

A
  • Allele frequencies will not change from generation to generation, given:
    > population is large
    > no immigration/emigration
    > no selection for/against particular alleles (natural selection)
    > no mutations
    > mating is random
31
Q

What is the Hardy-Weinberg equation?

A

p^2 + 2pq + q^2 = 1
p + q = 1

p = frequency of one allele of the gene (dominant)
q = frequency of one allele of the gene (recessive)
p^2 = frequency of homozygous dominant genotype
q^2 = frequency of homozygous recessive genotype
2pq = frequency of heterozygous genotype

32
Q

Explain why individuals within a population of a species may show a wide range of variation in phenotype

A
  • Genetic factors:
    > mutations = primary source of genetic variation
    > crossing over between homologous chromosomes during meiosis
    > independent segregation of homologous chromosomes during meiosis
    > random fertilisation of gametes during sexual reproduction
  • Environmental factors (depends on context, e.g food availability, light intensity)
33
Q

What is evolution?

A
  • Change in allele frequency over time/many generations in a population
  • Occuring through the process of natural selection
34
Q

Describe factors that may drive natural selection

A
  • Predation, disease and competition for the means of survival
  • These result in differential survival and reproduction, ie natural selection
35
Q

Explain the principles of natural selection in the evolution of populations

A
  1. Mutations - random gene mutations can result in new alleles of a gene
  2. Advantage - due to x selection pressure, the new allele might benefit its possessor (because …) —> organism has a selective advantage
  3. Reproductive success - possessors are more likely to survive and have increased reproductive success
  4. Inheritance - advantageous allele is inherited by members of the next generation (offspring)
  5. Allele frequency - over many generations, allele increases in frequency in the gene pool
36
Q

What is a gene pool?

A

The set of all genes, or genetic information, in any population, usually of a particular species

37
Q

Explain the effects of stabilising selection

A
  • Organisms with alleles coding for average/model variations of a trait have a selective advantage
  • So frequency of alleles coding for average variations of a trait increase and those coding for extreme variations of a trait decrease
  • So range/standard deviation is reduced
38
Q

Explain the effects of directional selection

A
  • Organisms with alleles coding for one extreme variation of a trait have a selective advantage
  • So frequency of alleles coding for extreme trait increase and those coding for other extreme variation decrease
39
Q

Explain the effects of disruptive selection

A
  • Organisms with alleles coding for either extreme variation of a trait have a selective advantage
  • So frequency of alleles coding for both extreme traits increase and average variation decreases
  • This can lead to speciation
40
Q

Describe speciation (how new species arise from existing species)

A
  1. Reproductive separation of 2 populations (of the same species)
  2. This can result in accumulation of differences in their gene pools
  3. New species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring
41
Q

Describe allopatric speciation

A
  1. Population is split due to geographical isolation (e.g new river formed)
  2. This leads to reproductive isolation, separating gene pools by preventing interbreeding/gene flow between populations
  3. Random mutations cause genetic variation within each population
  4. Different selection pressures/environments act on each population
  5. So different advantageous alleles are selected for/passed on in each population
  6. So allele frequencies within each gene pool change over many generations
  7. Eventually differet populations cannot interbreed to produce fertile offspring
42
Q

Describe sympatric speciation

A
  1. Population is NOT geographically isolated
  2. Mutations leads to reproductive isolation, separating gene pools by preventing interbreeding/gene flow within one population, e.g:
    > gamete incompatibility
    > different breeding seasons
    > different courtship behaviour preventing mating
    > body shape/size changes preventing mating
  3. Different selection pressures act on each population
  4. So different advantageous alleles are selected for/passed on in each population
  5. So allele frequencies within each gene pool change over many generations
  6. Eventually different populations cannot interbreed to produce fertile offspring
43
Q

Explain genetic drift and its importance in small populations

A

Genetic drift = a mechanism of evolution in which allele frequencies in a population change over generations due to to chance
- some alleles are passed onto offspring more/less often by chance
> regardless of selection pressures and whether alleles give a selective advantage
- so strongest effects in small populations as gene pool is small and chance has a greater influence
> e.g when population is sharply reduced in size = bottleneck effect
> e.g when a small, new colony forms from a main population = founder effect
- this can reduce genetic diversity - some alleles can become fixed or lost entirely

44
Q

What is a community?

A

All the populations of different species living in the same place (habitat) at the same time

45
Q

What is an ecosystem?

A

A community and the non-living (abiotic) components of its environment

46
Q

What does it mean by ‘ecosystems are dynamic’?

A

Their populations rise and fall over time

47
Q

What is a niche?

A
  • The specific role of a species within its habitat, e.g what it eats, where and when it feeds etc
  • Governed by its adaptation to both biotic and abiotic conditions
48
Q

Explain the advantage of species occupying different niches

A
  • Less competition for food/resources
  • If two species tried to occupy the same niche, one would outcompete the other
49
Q

What is carrying capacity?

A

The maximum (stable) population size of a species that an ecosystem can support

50
Q

List the factors that influence carrying capacity

A

ABIOTIC:
- light intensity, temperature, soil pH and mineral content, humidity
BIOTIC:
a) interspecific competition - between organisms of different species
b) intraspecific competition - between organisms of the same species
c) predation

51
Q

Explain how abiotic factors may affect population size/carrying capacity

A
  • If conditions favourable, organisms more likely to survive and reproduce —> increasing carrying capacity
  • e.g increasing light intensity increases rate of photosynthesis in plants
    > increase carrying capacity of a variety of plant species
    > so increases the number and variety of habitats, niches and food sources for animals
    > so increasing carrying capacity of a variety of animal species
52
Q

Explain how interspecific competition may affect population size

A
  • Reduces (named resource) available to both species, limiting their chances of survival & reproduction
    > reduces population size of both species
  • If one species is better adapted, it will outcompete the other
    > So population size of less well adapteds species declines, potentially leading to extinction
53
Q

Explain how intraspecific competition may affect population size

A
  1. As population size increases, resource availability per organism decreases, so competition increases
    > so chances of survival & reproduction decrease —> population size decreases
  2. As population size decreases, resource availability per organism increases, so competition decreases
    > so chances of survival & reproduction increase —> population size increases
54
Q

Explain the changes which occur in populations of predators and prey

A

Populations fluctuate in cycles, the predator population peaking after the prey (lag time):
1. Prey population increases so predators have more food
> so more predators survive and reproduce
2. Predator population increases so more prey killed & eaten
> so less prey survive and reproduce
3. Prey population decreases so predators have less food
> so less predators survive and reproduce
4. Predator population decreases so less prey killed & eaten
> so more prey survive and reproduce (cycle repeats)

55
Q

Describe how the size of a population of slow-moving/non-motile organisms can be estimated

A
  1. Divide area into grid/squres e.g place tape measures at right angles
  2. Generate a pair of random coordinates using a random number generator
  3. Place a quadratic here and count number/frequency of names species
  4. Repeat a large number of times (10 or more) and calculate a mean per quadrat
  5. Population size = (total area of habitat / quadrat area) x mean per quadrat
56
Q

Describe how the mark-release-recapture method can be used to estimate the size of a population of motile organisms

A
  • capture sample of species, mark and release
  • ensure marking is not harmful/does not affect survival
  • allow time for organisms to randomly distribute before collecting second sample
  • population = (number in sample 1 x number in sample 2) / number marked in sample 2
57
Q

What assumptions does the mark-releases-recapture method make?

A
  • limited/no immigration/emigration
  • sufficient time for marked individuals to mix/distribute evenly within the population
  • marking not removed and doesn’t affect chances of survival/predation
  • no/few births/deaths/breeding/change in population size (or birth & death rate are equal)
58
Q

Suggest why the mark-release-recapture method can produce unreliable results in very large areas

A
  • unlikely that organisms will distribute randomly/evenly
  • less chance of recapturing organisms (that were initially marked)
59
Q

Describe and explain how primary succession occurs

A

Succession = change in a community over time due to change in abiotic factors/species
1. Colonisation by pioneer species (first to colonise)
2. Pioneer species change abiotic conditions
> e.g they die and decompose, forming soil which retains water (humus/organic matter)
3. So environment becomes less hostile/more suitable for other species with different adaptations AND less suitable for previous species, so better adapted species outcompete previous species
4. As succession goes on, biodiversity increases
5. Climax community reached - final stable community (no further succession)

60
Q

Describe features of a climax community

A
  • same species present/stable community over a long time
  • abiotic factors (fairly) constant over time
  • populations (fairly) stable (around carrying capacity)
61
Q

Explain how conservation of habitats involves management of succession

A
  • Further succession can be prevented to stop a climax community from forming
    > by removing or preventing growth of species associated with later stages e.g by allowing grazing
  • Preserves an ecosystem at a certain point/in it’s current stage of succession (plagioclimax)
  • So early species are not outcompeted by later species and habitats/niches are not lost
62
Q

Describe the conflict between human needs and conservation as well as the importance of managing this

A
  • Human demand for natural resources is leading to habitat destruction/biodiversity loss
  • Conservation is needed to protect habitats/niches/species/biodiversity
  • Management of this conflict maintains the sustainability of natural resources
    > meeting current needs without compromising the ability of future generations to meet theirs

Y13 Biology (4 decks)

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