17. Selection & Evolution Flashcards
4 problems that may arise from artificial selection
- increase in homozygosity
- harmful recessive alleles may be expressed
- inbreeding depression / loss of hybrid vigour
- decrease in genetic variation
Bread wheat, Triticum aestivum, is a hexaploid that has developed from diploid wild grasses.
Outline the process by which T. aestivum has developed from wild grasses. [4m]
- cross between 2 wild grasses
- hybrid sterile
- chromosome doubling
- due to nondisjunction
- formation of tetraploid
- diploid gametes now formed
- new cross with diploid wild grass
- hybrid triploid
- hybrid sterile
- chromosome doubling into hexaploid
Explain how an environmental factor, such as the low concentration of oxygen in deep water, can act as a STABILISING FORCE in natural selection. [3m]
- in constant environment
- O2 concentration acts as a selective agent
- organisms best adapted to these conditions survive
- extreme phenotypes selected against
- narrow range of genetic variation
Explain how an environmental factor, such as the low concentration of oxygen in deep water, can act as an EVOLUTIONARY FORCE in natural selection. [3m]
- CHANGE in O2 concentration
- low O2 concentration acts as a selective agent
- some individuals in population are better adapted
- these are more likely to survive
- DIRECTIONAL SELECTION
+ populations develop in different conc. of O2
= DISRUPTIVE SELECTION
Breeding experiments in the lab show that M. lewisii and M. cardinalis can breed together and produce offspring. The F1 hybrid offspring are fertile.
Suggest, with reasons, what prediction can be made about the chromosome numbers of M. lewisii and M. cardinalis. [2m]
- same no. of chromosomes
- chromosomes (similar enough to) pair up
- meiosis can occur in hybrid
The F1 hybrids produce 50% fewer seeds than either of the 2 parent species.
Explain how the reduced production of seeds by the inter-species (F1) hybrids can act as a post-zygotic isolating mechanism. [2m]
- hybrids have fewer (F2) offspring
- outcompeted by parent species
- parent species are better adapted
- hybrid breakdown / hybrid line not sustained long-term
Suggest how copper ions reduce root growth. [2m]
- bind to membrane proteins
- inhibit active transport
- prevent uptake of mineral ions (eg. nitrates)
Explain why wild relatives of crop plants should be conserved. [2m]
- wild plants have greater variety of alleles
- could be useful for future breeding
- eg. of use - to cope with climate change / drought
5 conditions that must be present for speciation to occur
- Reproductive isolation
- Mutation
- Natural/directional selection
- Different environment/selection pressure
- Time
Explain why the experimental founder populations are at high risk of extinction. [3m]
- each island has a small population
- with low genetic diversity / small gene pool
- inbreeding depression
- environmental change may kill them all
