Genetics, Populations, Evolution & Ecosystems Flashcards
Define phenotype. (2)
- Expression of genetic constitution of an organism/genotype;
- And its interaction with the environment;
Define genotype. (1)
- The genetic constitution of an organism;
If a gene is sex-linked on the X chromosome, why is the phenotype more common in XY organisms? (2)
- Males have one allele;
Accept males only need one allele. - Females need two recessive alleles
Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation (2)
- Crossing over;
- Independent segregation/assortment (of homologous chromosomes);
- Random fertilisation;
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why (2)
- Small sample size;
- Fusion/fertilisation of gametes is random;
- Linked Genes;
- Epistasis;
- Lethal genotypes;
Name the relationship between two alleles when both alleles appear in the phenotype (1)
Co-dominance
Name the type of gene interaction when one gene affected the expression of another (1)
epistasis
Explain what it means when two genes are linked (1)
on same chromosome.
Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results? Give the reason for your choice of statistical test. (2)
- Chi squared test;
- Categorical data.
Define gene pool (1)
All the alleles in a population;
Define species (1)
(Organisms that) can breed together /
interbreed and produce fertile offspring;
The conditions under which the Hardy-Weinberg Principle applies (5)
- No mutations (arise);
- Random mating;
- Large population;
- Population is isolated / no flow of alleles
into or out of population; - No selection / all alleles equally likely to be passed on to the next generation
What are the two equations used in the Hardy-Weinberg equation (2)
- P + Q = 1
- p2 + q2 = 2pq = 1
Describe allopatric speciation (5)
- Geographical isolation;
- Reproductive separation/isolation OR No gene flow
OR Gene pools remain separate;
Accept no interbreeding but must be a separate idea from mp5 which relates to definition of a species.
Reject no inbreeding. - Different selection pressures;
- Variation due to mutations;
- Different allele/s passed on/selected OR Change in frequency of allele/s;
- Eventually different species cannot (inter)breed to produce fertile offspring;
Why does speciation take a long time? (3)
- Initially one/few animals with favourable
mutation/allele; - Individuals with (favourable) mutation/allele
will have more offspring; - Takes many generations for (favourable)
mutation/allele to become the most common allele (of this gene)
Natural Selection in Resistant Strains (5)
- Some individuals in population naturally resistant/not killed by pesticide/antibiotic;
- Due to mutation;
- These survive when pesticide/antibiotic
applied/non-resistant ones are killed; - To reproduce and pass on allele/gene (for
resistance); - Increase in frequency of allele for resistance;
Describe sympatric speciation (4)
- Not geographically isolated;
- Mutation causes reproductive isolation
- Gene pools kept separate/no gene flow;
- Different allele/s passed on / selected OR Change in frequency of allele/s
- Cannot breed/mate to produce fertile offspring
Define community (1)
All / group of species / all / group of
populations / all the organisms;
Mark, Release, Recapture – Assumptions (5)
- No emigration/immigration;
- No losses to predation;
- Marking does not affect survival;
- Birth rate and death rate equal;
- (In this case) all belong to one population;
Mark, Release, Recapture – Outline the method (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 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;
Describe how you could estimate the size of a population using random sampling (4)
- Use a grid
OR
Divide area into squares/sections; - Method of obtaining random coordinates/numbers e.g. calculator/computer/random numbers table/generator;
- Count number/frequency in a quadrat/section;
- Large sample and calculate mean/average number (per quadrat/section);
- Valid method of calculating total number of plant, e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrants/selections/m2 in area
Why repeat/ large sample size
So /representative;
Why random
Avoid bias;
The scientist used percentage cover rather than frequency to record the abundance of algae present. Suggest why (1)
too many to accurately count / individual
organisms not identifiable / too small to
identify / overlap;
Describe use of systematic sample to count plants (5)
- Systemic sampling (placing quadrat) at
regular intervals along transect line; - Transect line from/to ……..;
- Count number/frequency in a quadrat/section;
- Large sample and calculate mean/average number (per quadrat/section);
Effect of increased plant/animal diversity on ecosystem (3)
- Increase in plant diversity leads to more
different types of food for animals; - Increase in variety of animals leads to
increase in predator species; - Increase in more different niche/habitat;
Define niche (3)
- Niche is the role that a species plays within a community;
- Includes food resources;
- No two species can occupy identical niche;
Predator-Prey Relationship (4)
- As pest numbers increase more food or predators, so they increase;
- Increased predation of pests reduces numbers;
- Low number of pests results in less food for predators, so their numbers decrease;
- Low predator numbers allow pest population to rise as fewer are eaten;
Succession (5)
- (Colonisation by) pioneer species;
- Pioneers/species/organisms change the
environment/habitat/conditions/factors; - (Environment becomes) less hostile for other/new species
Accept previous species out-competed. - increase in diversity/biodiversity;
- (To) climax community
Give two features of a climax community.
- Same species present (over long time) / stable community (over long time);
- Abiotic factors (more or less) constant (over time)
- Populations stable (around carrying capacity)
Suggest one reason for conserving woodlands (1)
- Conserving / protecting habitats / niches;
- Conserving / protecting (endangered) species / maintains / increases (bio) diversity;
- Reduces global warming / greenhouse effect / climate change / remove / take up carbon dioxide;
- Source of medicines / chemicals / wood;
- Reduces erosion / eutrophication.
