Variation and Evolution (C2) Flashcards
What is continuous variation? shape of graph?
- phenotypes are controlled by a number/more than one gene e.g height, hair colour, skin colour
- environmental factors do have an effect (a plant may not grow tall despite having the alleles for tallness due to lack of sunlight)
- bell shapes curve, no gaps
What is discontinuous variation? shape of graph?
- phenotypes are controlled by a single gene e.g tongue rolling, ear lobes, blood type
- environmental factors have NO effect - the phenotype will remain the same regardless of external factors
- random variable graph, gaps between/distinct categories
What is non-heritable variation?
- where the environment can affect the way an organisms genes/phenotypes are expressed
- this variation cannot be passed on to offspring (unless an epigenetic change occurs - transcription of DNA/histone proteins is modified, the sequence is not but the expression is altered)
- e.g diet/nutrients, exercise, temperature, light
What is heritable variation? Increased by?
• this is genetic variation - sexual reproduction establishes new combinations of already present alleles, mutations may produce new alleles (can impact natural selection) may be passed on to offspring
• variation may be increased by;
crossing over in prophase I,
independent assortment in metaphase I and II,
mixing of two parental genotypes at fertilisation
What is the effect of inter and intra specific competition on breeding success and survival?
• competition places selective pressures on the survival of different phenotypes and hence breeding success (essentially driving natural selection)
What is selective pressure? selective agency examples? affects on organisms alleles?
• environmental factors which can alter allele frequencies of alleles present at a particular gene locus in a population
• SELECTIVE AGENCIES exert selection pressure
e.g supply of food, climate, breeding sites, human impacts
• organisms with well adapted phenotypes have alleles giving them a SELECTIVE ADVANTAGE therefore more likely to survive (having higher breeding success) than less well adapted, whose alleles are SELECTED AGAINST
What is the ‘gene pool’?
The total of all alleles for all of the genes in a population
( gene = portion of DNA that determines a certain trait, an allele is a specific form of a gene ie the gene for hair colour; the allele for brown hair)
What is genetic drift?
• can cause variation in allele frequencies due to CHANCE
natural selection is selected upon whereas genetic drift is due to chance
What is meant by allele frequency?
allele frequency refers to;
how common an allele is in a population
What is the Hardy Weinberg principle used for? what does it state? conditions needed?
• used to estimate frequencies of dominant or recessive alleles or of different genotypes of a characteristic in a population
• it states;
that the frequencies of dominant and recessive alleles, and genotypes will remain constant from one generation to the next, IF certain conditions remain true
- a LARGE population (100+ individuals)
- NO SELECTION for or against any phenotype
- RANDOM mating throughout the population
- NO MUTATIONS
- the population is ISOLATED, i.e. no immigration or
emigration
What is the Hardy Weinberg equation? which letter represents what?
p2 + 2pq + q2 = 1
where:
p = frequency of the DOMINANT ALLELE (i.e A)
q = frequency of the RESSESIVE ALLELE (i.e a)
(p + q = 1)
p2 = frequency of AA (homozygous dominant) 2pq = frequency of Aa (heterozygous) q2 = frequency of aa (homozygous recessive)
What is the concept of speciation?
when populations of a species become isolated new species can form - this is speciation
- evolution, in terms of speciation, will not take place if the conditions, under which the Hardy-Weinberg principle applies, do not change
- speciation, formation of a new species, can occur due to:
- GENETIC DRIFT in isolated population
- the FOUNDER EFFECT of disproportionate allele frequencies in small populations
- NATURAL SELECTION
What is the concept of isolation? types?
the separation of species, where demes (little populations/sub units to a species) become isolated form each other due to a barrier to reproduce
isolation can be:
- ALLOPATRIC isolation
- SYMPATRIC isolation
What is the definition of a species? when are two species distinguished/a new one formed?
• a group of phenotypically similar organisms that can INTERBREED to produce FERTILE offspring
*species are not classed as the same if they can not successfully interbreed to produce fertile offspring
What is the founder effect?
- when a new area is colonised by individuals from a population those individuals may have a gene pool which, due to chance, have brought different allele frequencies from the original gene pool
- through chance changes in allele frequencies (GENETIC DRIFT) or different SELECTION PRESSURES the founder population could become even more different from the original population - effect is more significant is smaller pops
