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2023-25 Biology > 7: Genetics, populations, evolution and ecosystems > Flashcards

7: Genetics, populations, evolution and ecosystems Flashcards

1
Q

Describe the process of succession [6]

A
  • (Colonisation by) [named] pioneer species;
  • Pioneers cause change in environmental abiotic / biotic factors (give an example);
  • Pioneers make the environment less hostile for new species;
  • New species change/make conditions less suitable for previous species;
  • Change/increase in diversity/biodiversity;
  • Stability increases [population/richness/abiotic factors];
  • Climax community [represented by…..];
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2
Q

Explain how succession results in a wide variety of fish living on coral reefs. [2]

A
  • Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; OR Increase in species richness / biodiversity
  • Provides more/different habitats/niches OR Provides greater variety/types of food OR becomes less hostile;
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3
Q

Describe random sampling
[estimation of population density]
[5]

A
  • Use a grid / split area into squares/sections OR Map the area
  • Method of obtaining random coordinates / numbers, e.g. random number generator;
  • Count number/frequency of plants in a quadrat;
  • Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
  • Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in area;
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4
Q

Describe systematic sampling [3]

A
  • Transect/lay line/tape measure (from one side of the dune to the other);
  • Place quadrats at regular intervals along the line;
  • Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;
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5
Q

Which type of sampling would you choose?

On a beach

A

RANDOM

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6
Q

Which type of sampling would you choose?

Along a beach

A

SYSTEMATIC

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7
Q

Which type of sampling would you choose?

In a wooded habitat

A

RANDOM

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8
Q

Which type of sampling would you choose?

On a coral reef

A

RANDOM

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9
Q

Which type of sampling would you choose?

Investigate how the distribution of species changes across a sandune away from the sea.

A

SYSTEMATIC

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10
Q

Describe how you would determine the mean percentage cover for beach grass on a sand dune. [3]

A
  • Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
  • Large number/sample of quadrats; (min 20)
  • Divide total percentage by number of quadrats/samples/readings;
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11
Q

Describe the mark, release, recapture technique [4]

A
  • Capture sample, mark and release;
  • Appropriate method of marking suggested / method of marking does not harm fish;
  • Take second sample and count marked organisms;
  • No in No in Population =
    (No in sample1 × No in sample2) divided by Number marked (recaptured) in sample 2;
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12
Q

The mark-release-recapture method can be used to estimate the size of a fish population.

Explain how. [4]

A
  • Capture/collect sample, mark and release;
  • Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival (of fish);
  • Allow (time for) fish to (randomly) distribute back into population before collecting a second sample;
  • (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured;
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13
Q

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes [2]

A
  • Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
  • Fish may remain in one area OR fish may congregate
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14
Q

Describe how you would determine how many quadrats to use when investigating a habitat. [5]

A
  • Calculate running mean/description of running mean;
  • When enough quadrats, this shows little change/levels out (if plotted as a graph);
  • Enough to carry out a statistical test;
  • A large number to make sure results are reliable and representative;
  • Need to make sure work can be carried out in the time available;
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15
Q

What is meant by carrying capacity?

A
  • Maximum number of individuals of each species an ecosystem can support.
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16
Q

Suggest two reasons for conserving rainforests.

A
  • Conserve/protect species/plants/animals/organisms OR For (bio)diversity;
  • Conserve/protect habitats/niches OR Provides/many habitats/niches; or conserve land for indigenous communities;
  • Reduces climate change;
  • Source of medicines/drugs/wood;
  • Reduces erosion/eutrophication;
  • (For) tourism;
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17
Q

Define: POPULATION

A

A group (of organisms) of the same species in the same area at the same time, that can interbreed to produce fertile offspring.

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18
Q

Define: Community

A

All the individuals of all the different species within the same area at the same time.

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19
Q

Define: Species richness.

A

The number of different species in a specific area at a specific time. (that make up a community)

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20
Q

What are the features of a CLIMAX COMMUNITY?

A
  • Stable populations of all species (unless environment changes)
  • Stable species richness (composition may change due to competition)
  • Stable Abiotic factors (unless environment changes)
  • Stable Biotic factors (unless invasive species introduced)
  • Wide variety of niches / habitats
  • Some fluctuations in birth / death rate due to change in dominant species
  • Stable NPP
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21
Q

Evolution may lead to….

A

SPECIATION

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22
Q

What is the PRIMARY SOURCE of genetic variation?

A

MUTATION

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23
Q

Variation in phenotypes within a population, is caused by:
1. ?
2. ?

A
  1. Expression of genotype;
  2. (and) interaction with the environment.
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24
Q

How can evolution be measured?

A

Changes to allelic frequencies over time

24
Q

Describe the process of succession [5]

A
  • (Colonisation by) pioneer species;
  • Pioneers cause change in environmental abiotic / biotic factors (give an example);
  • Pioneers make the environment less hostile for new species;
  • New species change/make conditions less suitable for previous species;
  • Change/increase in diversity/biodiversity;
  • Stability increases [population/richness/abiotic factors];
  • Climax community;
25
Q

Describe what is meant by speciation (allopatric) [5]

A
  • Geographical isolation;
  • Separate gene pools so no interbreeding (between populations);
  • Variation due to mutation;
  • Different environmental/abiotic/biotic conditions /** selection pressures; **
  • Selection for different / advantageous, features/characteristics/mutation/ allele;
  • Differential reproductive success / (selected) organisms survive and reproduce;
  • Leads to change in allelic frequencies;
  • Cannot breed/mate to produce fertile offspring.
26
Q

Describe what is meant by speciation (sympatric) [5]

A
  • NOT Geographical isolation;
  • Leads to **reproductive isolation **
  • Separate gene pools so no interbreeding (between populations);
  • Selection for different/advantageous, features/characteristics/mutation/ allele;
  • Differential reproductive success / (selected) organisms survive and reproduce;
  • Leads to change in allelic frequencies;
  • Cannot breed/mate to produce fertile offspring
27
Q

Name 4 reproductive isolation mechanisms [4]

A
  • Temporal (Timing)
  • Ecological (Habitat / niche)
  • Behavioural (Courtship)
  • Mechanical (Gamete release)
  • Gametic (can’t fuse)
  • Hybrid (infertile offspring)
28
Q

Define ‘genetic drift’.

A

Random change to allelic frequency within a (small) population.
E.g., Natural disaster (Forest fire) = Genetic bottleneck
Founder effect= small inbreeding population

28
Q

Define ‘gene flow’

A

The transfer of new alleles into different genepools. This may increase genetic diversity.

29
Q

Define ‘genepool’

A

All the alleles of all the genes within a population. (Same area at the same time).

30
Q

Describe how bacteria can become resistant to antibiotics [5]

A
  • Variation/variety within the population;
    • Mutation forms advantageous allele that leads to a protein that provides resistance from antibiotic (AR);
  • Bacteria with advantageous allele to survive in presence of antibiotic;
  • (Differential) reproductive success / adapted organisms reproduce(by binary fission);
  • Increase in frequency of AR allele within the population;
  • Plasmids with AR allele replicated and shared with other bacteria.
31
Q

What is meant by a genome?

A
  • (All) the DNA in a cell/organism;
  • ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
  • ‘the total number of DNA bases in a cell/organism’
32
Q

State three causes of genetic variation [3]

A
  • Mutation
  • Crossing over
  • Independent segregation (of homologous chromosomes)
  • Random fusion of gametes / fertilisation / mating
  • Produces new combinations of alleles.
33
Q

Explain how a single base substitution causes a change in the structure of a polypeptide [3]

A
  • Change in (sequence of) amino acid(s)/primary structure;
  • Change in position of hydrogen/ionic/disulfide bonds;
  • Alters tertiary structure;
  • No longer complementary / unable to bind to target molecule.
34
Q

What is meant by the term Genotype?

A
  • The genetic constitution of an organism.
35
Q

What is meant by the term phenotype [2]

A
  • Expression of genetic constitution / genotype / allele(s);
  • interaction with environment;
36
Q

What is meant by the term dominant allele?

A

Always expressed within the phenotype.
(even when heterozygous)

37
Q

What is meant by a recessive allele?

A
  • Only expressed when homozygous / not expressed in the heterozygote / not expressed if dominant present;
38
Q

State the rules for dominant alleles. [3]

A
  • Affected offspring MUST have at least one affected parent.
  • Unaffected parents ONLY have unaffected offspring.
  • If both parents are affected and have an unaffected offspring, both parents must be Heterozygous
39
Q

State the rules for recessive alleles. [1]

A
  • Unaffected parents can have an affected offspring (if they are Heterozygous)
40
Q

Define codominance

A
  • Both alleles (equally) expressed within the phenotype;
41
Q

How do multiple alleles of a gene arise?

A
  • mutations;
  • which are different / at different positions within the gene;
42
Q

Define epistasis

A
  • The expression of one gene alters/affects the expression of another gene within the phenotype.
43
Q

Define (Autosomal) gene linkage

A

Genes are on the same homologous pair of chromosomes (not the sex chomosomes)

44
Q

Independent segregation is:

Random or Rare?

A

RANDOM

All possible allele combinations are produced in equal numbers

45
Q

Crossing over is:

Random or Rare?

A

RARE

Only occurs between homologous chromosomes

If genes are linked…. new recombinant allele gametes are produced in very low numbers.

46
Q

An organism has the following genotype, the genes are linked.

AaBb

Assuming no crossing over takes place (as this is a rare process), what are the gamete genotypes produced.

A

AB & ab in equal numbers.

*Crossing over could produce fewer Ab & aB gametes.

47
Q

What are the Expected offspring phenotype ratios from heterozygous parents:

  1. Monohybrid
  2. Dihybrid
  3. Epistasis
  4. Autosomal linkage
A
  1. 3:1
  2. 9:3:3:1
  3. 9:4:3 or 15:1 or 9:7
  4. 3:1 (if no crosiing over) (no other pattern other than 4 phenotypes and recombination of alleles being the fewest)
48
Q

Define Sex linkage

A
  • The expression of an allele dependant on the gender of the individual as the gene is located on the sex chromosomes. (X chromosome)
49
Q

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why. [2]

A
  • (Recessive) allele is always expressed in males / males have one (recessive) allele;
  • Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;
50
Q

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

A
  • Small sample size;
  • Fusion/fertilisation of gametes is random;
  • Linked Genes / Sex-linkage / crossing over;
  • Epistasis;
  • Lethal genotypes/allele combinations;
51
Q

What is a gene pool?

A
  • All the alleles (of all the genes) in a population;
52
Q

What does Hardy Weinberg’s equation predict? [3]

A
  • The frequency/proportion of alleles (of a particular gene);
  • Will stay constant from one generation to the next/over generations / no genetic change over time;
  • Providing (2 from the following) no mutation/no selection/population large/population genetically isolated/mating at random/no migration;
53
Q

When would you use the Chi squared test?

A
  • Categoric data
  • To determine if there is a significant difference bewteen observed and expected ratios.
54
Q

P + q =

A

1

55
Q

What should the allele frequencies add up to?

A

1

P + q = 1

56
Q

Suggest why the sum of allele frequencies could be greater than 1.

A

More than one gene affects the expression of the phenotype.

(Alleles of more than one gene)

57
Q

Rules for pedigree diagrams:

A

Always:
1. Start at the bottom
2. Use the numbers of the individuals
3. Identify an offspring that has a different phenotype to BOTH of its parents
4. X Linked: Daughter (recessive) & Dad (must be recessive)
5. X linked: Son (dominant) & Mum (must be dominant)

2023-25 Biology (10 decks)

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