7.3 - Evolution may lead to speciation Flashcards
What is a gene pool? (1)
- All the alleles in a population
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 lowering times of the two species are different. Using this information, suggest how these two species of palm tree arose by sympatric speciation. (5)
- Occurs in the same habitat / environment / population
- Mutation/s cause different flowering times
- Reproductive separation / isolation / No gene flow / Gene pools remain separate
- Different allele/s passed on / selected / Change in frequency of allele/s
- Disruptive (natural) selection
- Eventually different species cannot (inter)breed to produce fertile offspring
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. Explain how different subspecies of giraffe may have evolved from a common ancestor. Use information from the passage in your answer. (5)
- No interbreeding / gene pools are separate / geographic(al) isolation
‘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
- Change/increase in allele frequency/frequencies
Lemmings often live in isolated populations. From time to time some lemmings move and join other populations. Explain how this movement is important in maintaining genetic variability in lemming populations which have large fluctuations in size. (2)
- Smaller populations have fewer different alleles / more homozygosity / less heterozygosity / smaller gene pool / lower genetic variability
- Migrants bring in new alleles / increase gene pool
James Bay is a large ocean bay in northern Canada. It was formed by the melting of glaciers. One species of lemming inhabits the eastern side of James Bay and another species of lemming inhabits the western side. Before the glaciers melted there was only one species of lemming present. Explain how two species of lemming evolved from the original species. (4)
- Geographical isolation of populations
- Variation present in population(s)
- Different environmental conditions / different selection pressures / different phenotypes selected
- Change in genetic constitution of populations / gene pools / allele frequency
Describe one way in which scientists could find out whether animals from two different populations belong to the same species. (2)
- Breed together
- If fertile offspring, then same species
Give two features of a climax community. (2)
- Same species present (over long time) / stable community (over long time)
- Abiotic factors (more or less) constant (over time)
- Populations stable (around carrying capacity)
Give two conditions for results from mark-release-recapture investigations to be valid. (2)
- Marking is not removed / marking does not affect survival / predation
- Limited / no immigration / emigration
‘accept ‘migration’ and descriptions of immigration / emigration - Sufficient time for (marked) individuals to mix (within the population)
- No deaths / breeding
- Sampling method is the same
Describe how you would investigate the distribution of marram grass from one side of the dune to the other. (3)
- Transect / lay line / tape measure (from one side of the dune to the other)
- Place quadrats at regular intervals along the line
‘accept references to stratified sampling / different seral stages - Count plants / percentage cover / abundance scale (in quadrats) / Count plants and record where they touch line / transect
The species that are present change during succession. Explain why. (2)
- Species / plants / animals change the environment / conditions / add humus / nutrients etc. / less hostile (habitat)
- Species / plants better competitors
In a population of snails, there is a range of phenotypic variation. State two possible factors that are responsible for the variation seen in snails. (2)
- Environmental influences / environment
- Genetic factors/genes/alleles/meiosis/mutation
The genetic variation in a gene pool is increased as a result of several factors. Identify one of these factors and explain how it gives rise to genetic variation. (2)
- Mutations
- Changes in the DNA base sequence give rise to new alleles
or - Meiosis
- New combinations of alleles result from crossing over / independent assortment
or - Random fertilisation
- The random fusion of gametes during fertilisation gives rise to new combinations of alleles in the zygote
List two different selection pressures that limit the size of a population. (2)
- Availability of resources/habitat/mates/food/water/ competition
- Predation / disease
- Temperature/rainfall / weather conditions
- Natural disasters / earthquakes/ floods/tsunamis/hurricanes
Describe the effect that stabilising selection has on a population. (2)
- Reinforces the average phenotype / selects against the extremes
- So that the mean value remains the same
State the meaning of the term genetic drift. (1)
- Allele frequencies of a population change by chance
