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Glossary of Biology 101 exam 3

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Created by jkadlik

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
male vs male competition
male- female choosy
Sexual selection in males
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
1. Femalechoiceofmales.
2. Needvariabilityinfemalesinchoice abilities.
3. Choicemustconferfitnessadvantageto some females. Better choosers will have higher fitness.
4. Variationinchoicebehaviormustbe heritable.


Evolution from genetic point of view
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
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
p2 + 2pq + q2 = 1
Note that if allele frequencies are known, genotype frequencies can be calculated.
And vice versa

processes that cause evolution
• non-random mating
• mutation
• small population size (genetic drift)
• migration (gene flow)
• natural selection



founder effect:
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.
– prezygotic • behavioral • ecological
• temporal • mechanical

– postzygotic • gamete incompatibility • hybrid inviability/sterility • lowered fitness of hybrids


Conditions necessary for speciation
• genetic isolation – gene flow restricted or blocked
• evolutionary divergence
– genetic drift, natural selection, sexual selection.

Allopatric isolation
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
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
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
population size * growth rate
N * r
logistic growth
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)
– predation • including parasitism
– availability of resources • e.g. food, space
– accumulation of wastes – behavior change

density-independent factors
– 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
o natural selection
o genetic drfit
o gene flow
o mutation


heterozygote advantage
when heterozygous individuals have higher fitness than homozygous individuals
directional selection
allele frequencies move in one direction

tends to reduce genetic diversity

sometimes results in fixed/ lost alleles



stabilizing selection
reduces extremes

no change in average value

genetic variation reduced



disruptive selection
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
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
the movement of alleles from one pop to another
reduces genetic differences
mutations
production of new alleles due to errors in DNA

mutations restore genetic diversity

evolutionary mechanism for nat selection



inbreeding
mating with relatives

always violates assumtions of hardy weinberg principle

inbreeding depression
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



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