Natural Selection

Question	Answer
G.D. and Heterozygote 4	G.D. decrease heterozygosity to decrease within a population over time Wright-Fisher Model Hetero. decrease by half in effective population size NZ Snapper stuck in lake
G.D. and Divergence 6	G.D. on island Eg 2 islands with 10 inhabitants each Begin - A1A2 heterozygous at neutral A locus Mating randomly and no migration/mutation = eventually islands fixed A1 or A2 SPECIATION EG Galapogos Island
No Foresight - No Purpose 3	No way to anticipate the future Favours changes that are immediately beneficial Evolution history if a lineage is contingent on genetic and environmental events
Natural Selection Depends On ... 2	Relationship between phenotype and genotypes/fitness = relation between fitness and genotype which determine whether or not evolutionary change occurs
Thomas Robert Malthus Principles of Population 4	Population growth food supply = famine or other checks on population Zone of between resources and population = in which nat. sel. by resource limitation occurs = in which less-fit forms are unable to survive
Fitness Ability of Individual (genotype) to survive (viability) and to reproduce (fertility) 2	Viability - probability of survival to reproductive age. Fertility - average number of offspring per individual that survive to reproductive maturity
Constraints to Natural Selection 2	HALDANE 1932 "Could produce a 'race' with the intellect of Shakespeare and stature of Carnea, but could not produce a race of angel"
Absolute Fitness 1	Average number of offspring (reproductive success) produced by individuals of a particular genotype
Relative Fitness 1	Average number of offspring produced by individuals of a particular genotype RELATIVE to other members of a population
Coat Colour of Oldfield Mice Peromysus polionotus 3	Light coated mice live on the beach Grey/ dark coated inland Variation within one population
Coat Colour of Oldfield Mice Genotype to Phenotype 4	Mc1R melacortin - 1 receptor gene Acts as a switch Contact with alpha-MSH melanocyte stimulating hormone - produce eumelanin = dark coat Contact with ASP agouti signal protein - produce phaeomelanin = light coat
Light Pocket Mice Dark Lava 4	60-98% survived probability of light phenotype to dark phenotype Selection co-efficient Larger = stronger action on nat. sel. = alleles change faster
Frequency-Independent Selection 9	Directional selection OVERDOMINANCE - heteroygote advantage (balancing selection) UNDERDOMINANCE - heterozygote disadvantgae Lead to FIXATION or ELIMINATION A1 dominant - initial increase in frequency most rapid - pace slows once common in pop. Co-do - dominant reaches fixation most rapidly Recessive - takes much longer to increase in freq. - Once common, fixation comes quickly
Overdominance 5	Heterozygote advantage Start at high/low freq., its freq. increases/decreases respectively Reach intermediate freq. (doesn't depends on initial freq.) so long as both alleles in pop. Hetero has higher fitness than homo. Direction of nat. sel. relies on allele frequency in pop.
Heterozygote Advantage Example 4	Sickle cell anaemia - Beta-haemoglobin locus Homo = severe anemia Hetero = middle anemia but parasite growth decreased Homo = normal
Underdominance 4	Heterozygote disadvantage No real world example within species/scare Practical implication of human autoimmune disease Lupus Chromo. rearrangements decrease fertility at meiosis in mouse/models
Positive Frequency Dependent Selection 5	Fitness associated with the trait (phenotype) increases as frequency of trait (genotype) increases in population Allele above critical threshold = reach fixation Allele below = lost from population Eg geographical ranges of butterfly Heliconics spps May favour genetic differentiation and long-term possibly speciation
Negative Frequency Dependent Selection (Inverse) 6	Fitness associated with trait (phenotype) increasesd as the freq. of trait of trait (genotype) decrease in population Balancing selection Allele starts at high freq. = phenotype common Low fitness = allele decline in freq. Allele starts low freq. = phenotype rare - high fitness = increased freq. Allele would eventually reach intermediate freq. of 2 polymorphs
Physical Constraints to Natural Selection 2	Ratio between fibia diameter and mass Fibia breaks down first when old limit on speed of horse by weight and strength of bone.
Convergent Evolution 3	Harvestman and cellular spider Convergent evolution of long thin legs = Distribute weight over large surface
Negative Frequency Dependent Selection Feeding Behaviour 3	Lake Tanganyika's scale eating cichlids LHS/RHS feeding Attack prey from behind - prey become more aware of one side = switch between morphs
Negative Frequency Dependent Selection Fihser's Sex Ratio 3	Sex ratio even in pop. Chromo. sex determination (mammals/birds) Each individual has mum and dad and contribute equally to ancestory of next gen = same average fitness
Negative Frequency Dependent Selection Fihser's Sex Ratio Explanation 9	Less female births than males = newborn female better mating than new male = have more offspring (females) = parents predispersed to have females = allele for female producing tendencies spreads = females become common 1:1 sex ration approached = Advantage for female sex dies away EVOLUTIONARY STABLE STRATEGY
Negative Frequency Dependent Selection Fihser's Sex Ratio Test 3	Samoan butterfly species 99% female and 1% male after infection with Wolbachia bacterium 2001 = varience that could produce many more males than females
Negative Frequency Dependent Selection Host-parasites 5	Host adapted and therefore resistant to parasites would have highest fitness Parasite population 'rare type' = advantageous and would be epected to spread Pare hosts adapted to increasingly common parasite have advantage over other hosts = maintain polymorphism = creat cycles of evolutionary change in host and parasite species
Co-evolution 4	MUTUALISM - evolutionary changes in each species benefit other species eg Humans and livestock Antagonistic co-evo. - evolutionary changes in each species decreases fitness for other species Evolutionary arms race
Predator-Prey Co-evolution 5	2 molluscs - one is predatory Sinistrofulgar (prey) and Mercenaria (predator) Different thickness of shell If predatory mollusc has thinner shell = breaks trying to get in
Predator-Prey Co-evolution 5	2 molluscs - one is predatory Sinistrofulgar (prey) and Mercenaria (predator) Different thickness of shell If predatory mollusc has thinner shell = breaks trying to get in
'Random' Selection 2	Chance or randomness when cause of event can result in several outcomes Can only specify probability/frequency of one/other outcome
Neutral Theory of Evolution 4	MOTTO KUMURA - neutral theory of molecular evolution in 68 Most variance in a population is selectively neutral Most changes in DNA or amino acid seq. over time and thus many molecular differences between populations related species are selectively neutral Differences due to GENETIC DRIFT
Genetic Drift 5	Process of random fluctuations in allele frequency due to sampling effect in finite populations G.D. and nat.sel. - 2 important causes of allele substitution G.D. in all natural populations as no such thing as an infinite population NAT.SEL. = ADAPTATION G.D. = NOT ADAPTATION
Genetic Drift and Natural Selection 3	Alleles at all loci are potentially subject to random to random genetic drift but not nat. sel. NEUTRALIST - SECTIONIST DEBATE - dispute about whether drift or selection is primary driver of evo. changes in sebset of mutations that reach high freq. in population G.D. is 'null hypothesis' to explain population different against which evidence for nat.sel. may be tested
Consequence of Genetic Drift 3	Finite pop. - allele freq fluctuate over time even without nat. sel. Some alleles fixed, others lost and fraction of hetero in proportion decrease over time Separate population diverse in term of allele freq. and in term of which alleles are present
Allele Freq. Fluctuate due to G.D. 7	Manx Cat breed Unsure what it was Picked up with ears without pain like a rabiit So said it was a cat-rabbit hybrid long ears, no tail, longer hind legs than forelegs Heterozygote lethal Small population = founder effect (G.D. and human selection)

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	Created by katy.lynock almost 11 years ago