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Variation
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- 1What is discontinuous variation? Give an exampleWhen characteristics have no intermediate types and are clear-cut. They are controlled by single genes so are monogenic e.g. Speckled or black moth
- 2What is continuous variation?Many possible values for a characteristic, and are controlled by many genes so are polygenic e.g. height or weight
- 3What is inter-specific competition?When organisms of different species compete for the same resources e.g. space, water
- 4What is intra-specific competition?Competition between organisms of the same species. E.g. Animals compete for nesting sites or mates
- 5What is selection pressure?An environmental factor that can alter the frequency of alleles in a population when it is limiting
- 6Give examples of some selection pressuresAvailability of nesting sites, Day length (affects reproduction), Overcrowding allows diseases to spread, predation, temperature, human impact
- 7How does natural selection work?A selection pressure causes mutation in organisms which produces an advantageous allele. The advantageous allele gives the organism a survival advantage so it outcompetes the other organisms in the species. It then reproduces, passing on the advantageous allele to its offspring
- 8What is the gene pool?All of the alleles present in a population at a given time
- 9What is the allele frequency?The frequency of an allele is its proportion, fraction or percentage of all the alleles of that gene in a gene pool
- 10What occurs to a population in a stable environment?If a sexually reproducing population is in a stable environment and there is no mutation and no immigration or emigration, the frequency of all the alleles stays constant
- 11What is genetic drift?Chance variation in allele frequencies in a population
- 12What is the Hardy-Weinberg principle?Used to calculate the frequency of alleles in the human gene pool associated with genetic diseases
- 13What is the equation for the Hardy-Weinberg principle?p2 + 2pq + q2 = 1
- 14Calculate the allele and genotype frequencies for this example- Sickle cell disease affects 9 in 100 in some parts of Africa. It is a genetically recessive alleleq2= 0.09
q= square root of 0.09= 0.3
(q+p)=1
p=1-0.3= 0.7
p2= 0.7 x 0.7 = 0.49= 49% of the population are genotypically normal
2pq= 2 x 0.7 x 0.3 = 0.42 = 42% of the population are carriers - 15What are the conditions for the Hardy-Weinberg principle?Organisms- Organisms are diploid, Allele frequencies are equal in both sexes, they reproduce sexually, mating is random, generations do not overlap
Population- Population size is very large, no migration (immigration or emigration) and no selection - 16What is evolution?The change in a phenotype of a species of a population over time
- 17What is speciation?The formation of a new species
- 18What is the founder effect?The loss of genetic variation in a new population established by a very small number of individuals from a larger population
- 19What is stabilising selection?When an average phenotype provides a greater advantage than either extreme. The extreme values are selected out, so the standard deviation will be smaller but a higher peak. Example= Birth weight- small babies are susceptible to infection and lose heat rapidly. Large babies have complications exiting the birth canal
- 20What is Directional selection?In a changing environment, an extreme phenotype may become advantageous. Over time, other values are selected against and the average phenotype changes.
- 21What is disruptive selection?In some situations, the average phenotype does not provide an advantage and is selected against. Over several generations, a lower and higher value are selected. Example= A population of salmon has large and small males. Large males gain access to females by fighting but small males gain access by sneaking. Average males cannot do either so are selected against
- 22What is pre-zygotic isolation?When gametes are prevented from fusing and so a zygote never forms
- 23What are the different types of pre-zygotic isolation?Geographical, behavioural, morphological, gametic and seasonal
- 24What is geographical isolation?When a population becomes split by a physical barrier into separate demes.
- 25What is behavioural isolation?When different mating behaviour stops mating between the whole population, eventually forming two separate mating groups
- 26What is allopatric and sympatric speciation?Allopatric is the evolution of species from demes isolated in different geographical locations, sympatric is when they share the same location
- 27What is morphological isolation?In animals, the reproductive parts must be complimentary for the sperm to be transferred to the female. In plants, the pollinator must be the same. This is to prevent genes mixing
- 28What is gametic isolation?Occurs in open environments such as oceans- fertilisation is stopped by:
1. chemo-attractants secreted by female gametes are only recognised by male gametes of the same species
2. The pollen of many species can germinate on the stigma of another species but the pollen tube only penetrates a small distance down the style - 29What is seasonal isolation?Reproductive organs of different species mature at different times of the year
- 30What is post-zygotic isolation?Gametes fuse and a zygote forms. Even if the organism develops and grows, it is sterile so the genes of the parent species are kept separate and the species do not merge
- 31What are the types of post-zygotic isolation?Hybrid sterility, Hybrid inviability, Hybrid breakdown
- 32What is hybrid inviabilityFertilisation occurs but incompatibility between the genes of the parents prevent development of an embryo
- 33What is Hybrid sterility?In some cases, an embryo formed from the gametes of two species can develop. But if the chromosomes are not sufficiently similar, they are unable to pair up at prophase I of meiosis so gametes cannot form. This means the hybrid is sterile
- 34What is hybrid breakdown?Some F1 hybrids are fertile, but the F2 are sterlie
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- AS level Biology Fichas sobre Variation, creado por Seren Jones el 15/05/2018.
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- Seren Jones
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