7: Genetics, populations, evolution and ecosystems Flashcards
Describe the process of succession [6]
- (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…..];
Explain how succession results in a wide variety of fish living on coral reefs. [2]
- 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;
Describe random sampling
[estimation of population density]
[5]
- 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;
Describe systematic sampling [3]
- 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;
Which type of sampling would you choose?
On a beach
RANDOM
Which type of sampling would you choose?
Along a beach
SYSTEMATIC
Which type of sampling would you choose?
In a wooded habitat
RANDOM
Which type of sampling would you choose?
On a coral reef
RANDOM
Which type of sampling would you choose?
Investigate how the distribution of species changes across a sandune away from the sea.
SYSTEMATIC
Describe how you would determine the mean percentage cover for beach grass on a sand dune. [3]
- 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;
Describe the mark, release, recapture technique [4]
- 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;
The mark-release-recapture method can be used to estimate the size of a fish population.
Explain how. [4]
- 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;
Suggest why the mark-release-recapture method can produce unreliable results in very large lakes [2]
- Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
- Fish may remain in one area OR fish may congregate
Describe how you would determine how many quadrats to use when investigating a habitat. [5]
- 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;
What is meant by carrying capacity?
- Maximum number of individuals of each species an ecosystem can support.
Suggest two reasons for conserving rainforests.
- 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;
Define: POPULATION
A group (of organisms) of the same species in the same area at the same time, that can interbreed to produce fertile offspring.
Define: Community
All the individuals of all the different species within the same area at the same time.
Define: Species richness.
The number of different species in a specific area at a specific time. (that make up a community)
What are the features of a CLIMAX COMMUNITY?
- 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
Evolution may lead to….
SPECIATION
What is the PRIMARY SOURCE of genetic variation?
MUTATION
Variation in phenotypes within a population, is caused by:
1. ?
2. ?
- Expression of genotype;
- (and) interaction with the environment.
How can evolution be measured?
Changes to allelic frequencies over time
Describe the process of succession [5]
- (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;
Describe what is meant by speciation (allopatric) [5]
- 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.
Describe what is meant by speciation (sympatric) [5]
- 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
Name 4 reproductive isolation mechanisms [4]
- Temporal (Timing)
- Ecological (Habitat / niche)
- Behavioural (Courtship)
- Mechanical (Gamete release)
- Gametic (can’t fuse)
- Hybrid (infertile offspring)
Define ‘genetic drift’.
Random change to allelic frequency within a (small) population.
E.g., Natural disaster (Forest fire) = Genetic bottleneck
Founder effect= small inbreeding population
Define ‘gene flow’
The transfer of new alleles into different genepools. This may increase genetic diversity.
Define ‘genepool’
All the alleles of all the genes within a population. (Same area at the same time).
Describe how bacteria can become resistant to antibiotics [5]
- 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.
What is meant by a genome?
- (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’
State three causes of genetic variation [3]
- Mutation
- Crossing over
- Independent segregation (of homologous chromosomes)
- Random fusion of gametes / fertilisation / mating
- Produces new combinations of alleles.
Explain how a single base substitution causes a change in the structure of a polypeptide [3]
- 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.
What is meant by the term Genotype?
- The genetic constitution of an organism.
What is meant by the term phenotype [2]
- Expression of genetic constitution / genotype / allele(s);
- interaction with environment;
What is meant by the term dominant allele?
Always expressed within the phenotype.
(even when heterozygous)
What is meant by a recessive allele?
- Only expressed when homozygous / not expressed in the heterozygote / not expressed if dominant present;
State the rules for dominant alleles. [3]
- 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
State the rules for recessive alleles. [1]
- Unaffected parents can have an affected offspring (if they are Heterozygous)
Define codominance
- Both alleles (equally) expressed within the phenotype;
How do multiple alleles of a gene arise?
- mutations;
- which are different / at different positions within the gene;
Define epistasis
- The expression of one gene alters/affects the expression of another gene within the phenotype.
Define (Autosomal) gene linkage
Genes are on the same homologous pair of chromosomes (not the sex chomosomes)
Independent segregation is:
Random or Rare?
RANDOM
All possible allele combinations are produced in equal numbers
Crossing over is:
Random or Rare?
RARE
Only occurs between homologous chromosomes
If genes are linked…. new recombinant allele gametes are produced in very low numbers.
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.
AB & ab in equal numbers.
*Crossing over could produce fewer Ab & aB gametes.
What are the Expected offspring phenotype ratios from heterozygous parents:
- Monohybrid
- Dihybrid
- Epistasis
- Autosomal linkage
- 3:1
- 9:3:3:1
- 9:4:3 or 15:1 or 9:7
- 3:1 (if no crosiing over) (no other pattern other than 4 phenotypes and recombination of alleles being the fewest)
Define Sex linkage
- The expression of an allele dependant on the gender of the individual as the gene is located on the sex chromosomes. (X chromosome)
Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why. [2]
- (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;
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why.
- Small sample size;
- Fusion/fertilisation of gametes is random;
- Linked Genes / Sex-linkage / crossing over;
- Epistasis;
- Lethal genotypes/allele combinations;
What is a gene pool?
- All the alleles (of all the genes) in a population;
What does Hardy Weinberg’s equation predict? [3]
- 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;
When would you use the Chi squared test?
- Categoric data
- To determine if there is a significant difference bewteen observed and expected ratios.
P + q =
1
What should the allele frequencies add up to?
1
P + q = 1
Suggest why the sum of allele frequencies could be greater than 1.
More than one gene affects the expression of the phenotype.
(Alleles of more than one gene)
Rules for pedigree diagrams:
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)
