Cellular Control, (Pt 4) Bio

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Cellular Control, (Pt 4) Bio
2013-04-25 12:57:14
cellular control biology a2 genetics

Population genetics,roles of genes and environment in evolution, what is a species?, natural and artificial selection
Show Answers:

  1. What is a gene pool?
    The complete range of alleles (genetic information) present in a population.
  2. New alleles are usually generated by ___ in genes. How often an allele occurs in a population is called the ___ ___. The __ __ in a population changes over time - this is ___.
    • mutations
    • allele frequency
    • allele frequency
    • evolution
  3. Why did scientists start to look at population genetics? Also, what is population genetics?
    • As they studied evolution, they realised that populations, rather than individuals, are the functional units in this process.
    • Scientists realised that they needed to consider the frequency of alleles in the population
    • In population genetics, biologists focus on the genetic structure of populations. They measure changes in alleles and in genotype frequency from generation to generation.
  4. To measure the frequency of an allele, we need to know: (2)
    • The mechanism of inheritance of a particular trait (is it codominant, recessive, dominant? etc)
    • How many different alleles of the gene for that trait are in the population
  5. For traits that show codiminance, the frequency of the heterozygous phenotype is the same as the frequency for the ___ ___. Give examples to show why the frequency of codominant alleles can be found in population.
    • heterozygous genotype
    • eg. MN blood group must contain one M and one N
    • M blood will mean genotype MM
    • N blood means genotype NN.
    • (If one allele is recessive, then it's frequency cannot be directly determined, so Hardy-Weinberg principle must be used).
  6. So, why do we not need the Hardy-Weinberg principle to calculate frequency of codominant alleles?
    Because both alleles contribute to the phenotype, the genotypes of all phenotypes are known.
  7. What 4 assumptions does the Hardy-Weinberg principle make? (In other words, it only works under certain conditions, what are they?)
    • Population is very large (this eliminates sampling error)
    • Mating within population is random
    • There's no selective advantage for any genotype
    • There's no mutation, migration or genetic drift.
  8. Individuals have ___, populations have __ ___.
    • genomes
    • gene pools
  9. What are the 2 Hardy-Weinberg equations?
    • p+q = 1
    • p2+2pq+q2 = 1
    • [where p=frequency of dominant allele; q=freq of recessive allele; p2=freq of homozygous dominant genotype; q2=freq of homozygous recessive genotype; 2pq=freq of heterozygous genotype]
    • Don't forget, frequency is in forms like 0.6, 0.1 etc
    • By using these equations, you can work out the allele frequency and the genotype frequency. (esp for genotype frquency, might need to use both equations)
  10. What factors can alter the amount of genetic variation within a population? (5)
    • Size of population
    • Randomness of mating
    • Mutation
    • Competition
    • Selection
  11. Give examples of environmental factors that limit the growth of a population and keeps it steady/stable.
    • Space (for plants to grow, or animals to feed)
    • Availability of food
    • Light
    • Minerals and water 
    • Some are abiotic and some are biotic
    • [Over time the population size will fluctuate around a mean level.]
  12. Explain, with examples, how environmental factors can act as a stabilising force of natural selection.
    • When environment isn't changing much, individuals with alleles for characteristics towards the middle of the range (average) are more likely to survive and reproduce. It reduces range of possible phenotypes. This is called stabilising selection
    • Eg. The selection pressure of predators increases chance of alleles for agouti coat for mice being passed on, whereas black or white coat mice are more likely to be eaten.
  13. Explain, with examples, how environmental factors can act as an evolutionary force of natural selection.
    • When there's a change in the environment, individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This is called directional selection .So the allele frequency in gene pool is shifted.
    • Eg. Climate might change and ground might be covered in snow. Then those rabbits with white fur would now have a selective advantage. The frequency of these alleles in gene pool would change,as would the phenotype.
    • "Directional selection leads to evolutionary change, so it is an evolutionary force of natural selection".
  14. A large population of organisms may be split into sub-groups by various ___ ___. List the different types of these. Give examples of each.
    • Isolating mechanisms
    • Ecological (geographic) barriers, such as a river or mountain range
    • Seasonal (temporal) barriers, such as climate change 
    • Reproductive mechanisms, members may no longer be able to physically mate - their genitals may be incompatible or breeding seasons/courtship behaviour may vary.
  15. What is the result of these isolating mechanisms? And what is its role in evolution of new species?
    • This leaves two sub-populations, isolated from each other.
    • In each case different alleles will be eliminated or increased within each sub-population. 
    • Eventually the sub-populations will not be able to interbreed and will be different species.
  16. REMEMBER: when answering questions about selection, always refer to increasing chances of favourable ___ (don't say ___ ) being passed on to offspring.
    • alleles
    • genes
  17. What is genetic drift?
    • The change in allele frequency in a population, due to some alleles being passed onto the next generation (by chance I think) and some being passes on less. This causes some phenotypic traits to become rarer or more common.
    • Also called allelic drift
  18. ___ ___ and ___ ___ work alongside each other to drive evolution, but one process can drive evolution more than the other depending on the ___ ___.
    • Natural selection
    • genetic drift
    • population size
  19. Evolution by genetic drift causes large changes in ___ populations. Why?
    • smaller (sometimes when there's a genetic bottleneck when large pop become suddenly smaller due to disaster etc).
    • Because as population decreases, chance has greater influence - the degree of fluctuation of allele frequency will increase. (In extreme cases, genetic drift may lead to chance elimination of one allele from population).
    • In larger populations, however, chance factors tend to even out across the whole population because there is more of them.
  20. What are the two concepts of species we need to know about?
    • Biological species concept 
    • Phylogenetic (evolutionary) species concept
  21. What is the biological species concept?
    • A group of similar organisms that can interbreed and produce fertile offspring and is reproductively isolated from other such groups.
    • Problems: When biologists want to classify living organisms that do not reproduce sexually.
    • They may not be able to observe their reproductive behaviour (you don't know if they produce fertile offspring together - because they might be extinct, practical and ethical issues, asexual reproduction).
    • Some members of same species may look very different (eg. the male and females look very different)
  22. What are some of the problems with the biological species concept?
    • When biologists want to classify living organisms that do not reproduce sexually.
    • They may not be able to observe their reproductive behaviour (you don't know if they produce fertile offspring together - because they might be extinct, practical and ethical issues, asexual reproduction).
    • Some members of same species may look very different (eg. the male and females look very different)
  23. What is the phylogenetic species concept?
    • A groups of organisms that have similar morphology (shape), physiology (biochemistry), embyology (stages of development) and behaviour, and occupy the same ecological niche.
    • (I think, maybe study of evolutionary connection between organisms and their DNA is also included, and in this sense, called cladistic species concept too? CHECK).
  24. Give some advantages and disadvantages of biological species concept and phylogenetic species concept.
    • Biological species concept: gives clear-cut definition (it can either inter-breed or not). But limited because it can only be used for sexually reproducing organisms and because we often don't have enough info.
    • Phylogenetic species concept: Allows us to determine species of non-sexually reproducing organisms (such as bacteria) and exitinct ones from fossils etc. (But not as rigorous and open to subjectivity?)
  25. List the similarities between natural selection and artificial selection. (2)
    • Both change the allele frequencies in the next generation - the alleles that code for the desirable characteristic will become more common in the next generation.
    • Both may make use of random mutations when they occur - if random mutation produces allele that gives desirable phenotype, it will be selected for in the next generation.
  26. List the differences between natural selection and artificial selection. (4)
    • In natural selection, organisms that reproduce are selected by environment; but in artificial this is carried out by humans.
    • Artificial selection aims for predetermined result (eg higher yield of milk), but in natural selection the result is unpredictable.
    • Natural selection makes species better adapted to environment, but artificial selection makes species more useful for humans.
    • Artificial selection is much quicker than natural selection in bringing about changes.
  27. How has artificial selection been used to produce the modern dairy cow?
    • Farmers select a female with very high milk yield and a male who have produced daughters with high milk yields (in progency tests) (or had mother with v.high milk yield).
    • Only few good-quality bulls need to be kept as semen from bull can be collected and used to artificially inseminate many cows.
    • Some elite cows given hormones so they produce many eggs.
    • Eggs fertilised in vitro and embryos implanted into surrogate mothers. These embryos could also be cloned to make many more offspring.
    • In these ways, a few elite cows can produce more offspring than they would naturally.
    • Then, offspring with highest milk yields selected again and bred together, and this is continued over several generations.
  28. Give 4 examples of characteristics that are desired in wheat.
    • Resistance to fungal infections
    • High protein content
    • Straw stiffness (and resistance to lodging - so bending over in wind etc)
    • High yield
  29. How has artificial selection been used to produce bread wheat, Triticum aestivum?
    • Wheat plants with high wheat yield and other desirable characteristics are bred together. Best offspring bred together. Continued over several generations to produce plant with very high yields.
    • Artificial selection was used to produce wheat that has 6 sets of chromosomes (6n) instead of the usual 2n by breeding those with the mutation to double chromosome number - so cells become bigger - better.
    • (Wild wheat crossed with wild grass. A sterile hybrid is produced.By mutation, its chromosome number doubles, and now it becomes fertile, select this and bread with another grass etc..)