T7 Genetics, Populations, Evolution and Ecosystems Flashcards
In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r.
(a) Male fruit flies are more likely than female fruit flies to have white eyes.
Explain why. 2 marks
- Males have one allele;
Accept males only need one allele. - Females need two recessive alleles
OR
Females must be homozygous recessive
OR
Females could have dominant and recessive alleles
OR
Females could be heterozygous/carriers;
Ignore references to X and Y chromosomes.
Accept r as recessive allele and R as dominant allele.
If no reference to allele, accept for one mark male needs one
recessive gene whereas females need two recessive genes.
What is meant by the term phenotype? 2 marks
- (Expression / appearance / characteristic due to) genetic constitution / genotype /
allele(s); - (Expression / appearance / characteristic due to) environment;
- Accept: named characteristic.
- Accept: homozygous / heterozygous / genes / DNA.
- Ignore: chromosomes.
What does the Hardy–Weinberg principle predict? 3 marks
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 no mutation / no selection / population large / population
genetically isolated / mating at random / no migration;
The three principles for marking are:
What feature
What happens to it
Providing . . .
Accept: genotype / explanation of genotype
Accept: alternative wording, e.g. there is no gene flow / genetic drift
for genetically isolated
What is a gene pool? 1 mark
All the alleles in a population;
Accept: The number of alleles in a population.
Note: All or number of alleles in a species on its own is not enough
on its own.
Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different.
Using this information, suggest how these two species of palm tree arose by sympatric speciation. 5 marks
- Occurs in the same habitat / environment / population;
- Mutation/s cause different flowering times;
- Reproductive separation / isolation
OR
No gene flow
OR
Gene pools remain separate; - Different allele/s passed on / selected
OR
Change in frequency of allele/s - Disruptive (natural) selection;
- Eventually different species cannot (inter)breed to produce fertile offspring;
- Accept: are not geographically isolated / separated.
- Accept: same place
- Accept: no interbreeding but must be a separate idea from
mark point 6 which relates to definition of a species.
Note: Answers relating only to allopatric speciation = 3 max, mark
points 3, 4 and 6.
There are nine subspecies of giraffe. These subspecies evolved when populations of giraffe were separated for long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to six of these subspecies should be classified as different species.
(a) Explain how different subspecies of giraffe may have evolved from a common ancestor.
Use information from the passage in your answer. 5 marks
- No interbreeding / gene pools are separate / geographic(al) isolation;
Accept: reproductive isolation as an alternative to no interbreeding. - Mutation linked to (different) markings/colours;
- Selection/survival linked to (different) markings/colours;
- Adapted organisms breed / differential reproductive success;
Note: ’passed on to offspring’ on its own is not sufficient for
reproduction. - Change/increase in allele frequency/frequencies;
Biologists compared the mitochondrial DNA of the different subspecies of giraffe. They used the results from comparing this DNA to conclude that six of the nine subspecies are separate species.
Suggest how they came to this conclusion. 2 marks
- (Compare DNA) base sequence / base pairing / (DNA)
hybridisation;
Ignore: compare chromosomes / ‘genetic make-up’.
Accept: (compare) genes / introns / exons.
Note: reference to only comparing alleles is 1 max. - Different in six (species) /different in different species / similar in
three (subspecies) /similar in same species/subspecies;
Ignore: compare chromosomes / ‘genetic make-up’.
Reject: ‘ same alleles/ same DNA bases in three
species/subspecies’.
Note: mark point 2 can be awarded without mark point 1.
Lake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.
(a) Describe one way in which scientists could find out whether cichlids from two different
populations belong to the same species. 2 marks
breed together;
if fertile offspring, then same species;
Lake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.
During the last 700 000 years there have been long periods when the water level was much lower and Lake Malawi split up into many smaller lakes. Explain how speciation of
the cichlids may have occurred following the formation of separate, smaller lakes.
4 marks
isolation of two populations;
variation already present due to mutations;
different environmental conditions / selection pressures leading to
selection of different features and hence different alleles;
different frequency of alleles;
separate gene pools / no interbreeding
Many species of cichlids are similar in size and, apart from their colour, in appearance.
Suggest how the variety of colour patterns displayed by these cichlids may help to maintain the fish as separate species. 2 marks
selection of mate dependent on colour pattern;
prevents interbreeding / keeps gene pools separate;
The stream eventually recovered to reach a climax community.
Give two features of a climax community. 2 marks
- Same species present (over long time) / stable community (over long time);
- Abiotic factors (more or less) constant (over time)
- Populations stable (around carrying capacity)
The student used the mark-release-recapture technique to estimate the size of the population of sand lizards on an area of moorland. She collected 17 lizards and marked them before releasing them back into the same area. Later, she collected 20 lizards, 10 of which were marked.
(i) Give two conditions for results from mark-release-recapture investigations to be
valid. 2 marks
- Marking is not removed / marking does not affect survival / predation;
- Limited / no immigration / emigration;
Accept ‘migration’ and descriptions of immigration / emigration - and 4. Increase / decrease in population is not sufficient – there
must be a reason - Sufficient time for (marked) individuals to mix (within the population);
Accept – ‘For mixing to occur between samples’ - No / little births / deaths / breeding;
- Sampling method is the same;
Ignore ‘random sampling’
In northern India, there is a conflict of interests between farmers of livestock (eg cows) and people trying to conserve ibex (a type of wild goat).
When livestock are given extra food, their populations can grow too large and compete with ibex.
(a) Name the type of competition between livestock and ibex. 1 mark
Interspecific (competition);
The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The
soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The
sundew can trap and digest insects.
(a) Describe how you could estimate the size of a population of sundews in a small marsh. 5 marks
1. Use a grid
OR
Divide area into squares/sections;
Accept use of tape measures/map/area with coordinates.
Accept Belt transect.
2. Method of obtaining random coordinates/numbers e.g. calculator/computer
/random numbers table/generator;
If transect method used accept quadrats at regular intervals or current
mark point 2.
3. Count number/frequency in a quadrat/section;
Accept % cover in quadrat/section.
Ignore amount/abundance.
4.Large sample and calculate mean/average number (per quadrat/section);
Accept large sample and calculate mean %.
Accept large sample and method of calculating mean.
Accept many/multiple for large sample but ignore several.
If a specific number is given it must be 10 or more.
5.Valid method of calculating total number of sundews, e.g. mean number of
plants per quadrat/section/m2
multiplied by number of quadrats/sections/m2
in marsh;
Do not allow ‘scale up’ without further qualification.
Do not award if % cover determined.
The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The
sundew can trap and digest insects.
Suggest and explain how digesting insects helps the sundew to grow in soil with very low
concentrations of some nutrients. 2 marks
Mark in pairs 1 and 2, or 3 and 4.
Ignore carbohydrates, lipids or named carbohydrate/ lipid.
1. Digestion/breakdown of proteins;
2. Provides amino acids
OR
(Sundew can) produce a named (organic) nitrogen-containing compound e.g.
proteins, amino acids, DNA, ATP;
Ignore if nitrate or ammonium ions given as products.
3. Digestion/breakdown of named (organic) phosphate-containing compound e.g.
DNA, RNA;
4. Provides named (organic) phosphate-containing product e.g. nucleotides
OR
(Sundew can) produce a named phosphate-containing compound e.g. ATP,
DNA;
Accept phosphate as a named product.
Dengue is a serious disease that is caused by a virus. The virus is carried from one person to
another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation.
(a) Explain how using the SIT could reduce transmission of dengue. 2 marks
- Compete (with fertile males) to mate / for food / resources
OR
intraspecific competition; - Do not reproduce / breed
OR
Reduces population (of mosquitoes); - Must convey idea of competition.
- Accept: ‘fewer mosquitoes’ / ‘fewer offspring’.
Describe how the mark-release-recapture method could be used to determine the
population of mosquitos at the start of an investigation. 3 marks
- Capture / collect / sample, mark and release;
- Leave time for mosquitoes / Aedes to disperse before second sampling /
collection; - (Population =) number in first sample × number in second sample divided by
number of marked in second sample / number recaptured; - Accept: correct equation.
What is a species? 1 mark
(Organisms that) can breed together / interbreed and produce fertile offspring;
Need both aspects. Reject ‘inbreed’
Reject viable offspring
What is meant by uniformly distributed?
Same number (of organisms) in each region / (organisms) equally spread;
Allow other ways of expressing ‘region’ or ‘equally spread’, eg not
clumped together, same number per unit area
Genotype definiton 1 mark
Genetic makeup of an organism
What is adaptive radiation? 1 mark
When a population evolves to adapt to its local environment due to selection pressure
Definiton of a gene 1 mark
A section of DNA that codes for a polypeptide and a functioning mRNA
Definition of an allele 1 mark
A different form of a gene
What does Polygenetic mean? 1 mark
Two or more genes contribute to the phenotypic expression of a single characteristic e.g. skin colour
