Biology 101 exam 3
Terms
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Frequency-dependent
selection: - the phenotype that yields the greatest fitness depends on how common each alternative phenotype is.
- sexual dimorphism
- pattern: seems to act more strongly on males; traits that respond to sexual selection are more elaborate in males.
- types of sexual selection
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male vs male competition
male- female choosy - Sexual selection in males
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1. MaledominanceorExtravaganttrait.
2. Needvariabilityamongmalesinthese traits.
3. Traitsconferfitnessadvantagetosome males. For some males in the population the benefit in reproduction must be above and beyond survival cost.
4. Variationmustbeheritable. - sexual selection in females
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1. Femalechoiceofmales.
2. Needvariabilityinfemalesinchoice abilities.
3. Choicemustconferfitnessadvantageto some females. Better choosers will have higher fitness.
4. Variationinchoicebehaviormustbe heritable. - Evolution from genetic point of view
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population: all of the individuals of a
species in a single place.
locus: a particular location on a particular chromosome; usually a gene.
allele: a variant form of a gene; a locus
typically has two or more alleles. - evolution from genetic point of view continued
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gene pool: total aggregate of all alleles in a population at any one time.
allele frequency: at a given locus (or loci), the proportion of a gene pool that is made up of a particular allele.
genotype frequency: at a given locus (or loci), the proportion of individuals that have a particular genotype - The Hardy-Weinberg model
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p2 + 2pq + q2 = 1
Note that if allele frequencies are known, genotype frequencies can be calculated.
And vice versa - processes that cause evolution
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⬢ non-random mating
⬢ mutation
⬢ small population size (genetic drift)
⬢ migration (gene flow)
⬢ natural selection - founder effect:
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colonization of new or isolated habitat by a few individuals. – important factor in evolution on islands
– in humans, can cause high incidence of inherited disorders, e.g. Ellis-van Creveld syndrome in Lancaster County Amish. - Reproductive isolating mechanisms prevent interbreeding.
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– prezygotic • behavioral • ecological
• temporal • mechanical
– postzygotic • gamete incompatibility • hybrid inviability/sterility • lowered fitness of hybrids - Conditions necessary for speciation
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• genetic isolation – gene flow restricted or blocked
• evolutionary divergence
– genetic drift, natural selection, sexual selection. - Allopatric isolation
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a population is sub-divided into two or more geographically separated parts.
– colonization of newly-formed islands.
– rising sea level isolates former part of mainland as an island.
– geological change, e.g. mountain building.
– formation of islands of habitat, e.g. after climate change.
– continental drift – plate tectonics - Per capita birth and death rates
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per capita birth rate:
1500 births ÷ 10,000 people = 0.15 births/person/year
per capita death rate: 500 deaths ÷ 10,000 people = 0.05 deaths/person/year - per capita growth rate
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r=b-d
(b = per capita birth rate,
d = per capita death rate) - Per capita growth rate (increase, decrease, stabilize)
- r > 0, population is growing r < 0, population is shrinking r = 0, population is stable
- Exponential growth rate
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population size * growth rate
N * r - logistic growth
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Population size increases at a increasing rate and then at a diminishing rate, until it reaches a limit called the carrying capacity (K).
dN/dt =rmaxN (K-N / K) - ⬢ density-dependent factors (effects increase as population density increases)
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– predation • including parasitism
– availability of resources • e.g. food, space
– accumulation of wastes – behavior change - density-independent factors
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– weather
• e.g. annual freezes, periodic droughts/floods, unpredictable storms, etc. - Vicariance
- a form of speciation that occurs when a population is subdivided by a geographic barrier.
- Colonization
- occurs when a subset of a population establishes a new population in a novel location.
- Dispersal
- occurs when a subset of a population moves to a novel location.
- four mechanisms that shift allele frequencies
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o natural selection
o genetic drfit
o gene flow
o mutation - heterozygote advantage
- when heterozygous individuals have higher fitness than homozygous individuals
- directional selection
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allele frequencies move in one direction
tends to reduce genetic diversity
sometimes results in fixed/ lost alleles - stabilizing selection
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reduces extremes
no change in average value
genetic variation reduced - disruptive selection
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eliminates phenotypes near the average value and favors extremes
tends to maintain the amount of genetic variation in a population
can lead to speciation - Genetic drift
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any change in allele frequency that is due to chance in a population
can lead to random loss / fixation
most pronounced in small pop - population bottleneck
- when a large population experiences a sudden reduction in size
- gene flow
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the movement of alleles from one pop to another
reduces genetic differences - mutations
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production of new alleles due to errors in DNA
mutations restore genetic diversity
evolutionary mechanism for nat selection - inbreeding
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mating with relatives
always violates assumtions of hardy weinberg principle - inbreeding depression
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loss of fitness that takes place when homozygosity increases and heterozygosity decreases
results from
o many recessive cells represent loss of function mutations
o many genes are under intense selection for heterozygote advantage