3. Adaptions and Natural Selection
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- nature chooses the designs that work best in any given circumstance and therefore shapes organisms to meet the challenges they face
favorable traits that accumulate over time
carrying two copies of each gene
half of the chromosomes
alternative versions of a gene that can occur at the same locus
two alleles match at a locus
two alleles differ at a locus
how do genes affect phenotypes
by coding for proteins
heritability depends on... 3
- 1. phenotypic variation
- 2. genetic variation
- 3. environmental variation
0 heritiability means
all variation is due to environment. none of the differences are caused by genetic differences.
constraints on NS perfection
- cost - it must pay for itself in reproductive success
- variation - selection only chooses what already exists
- time - if environment changes too quickly, NS cant keep up.
- track environmental changes and adjust phenotype accordingly
- ex. pupil size
a particular pattern of response to environment
adaptions that resist environmental influence
occur when the facultative responses of an organism are overwhelmed
heritability of facultative adaptions
low, they are environmental responses.
how does selection shape facultative responses?
- through the expression, through reaction norms.
- reaction norms can be highly variable
the front door to the next generation
a gene that increases the fitness of its average carrier will eventually spread.
the back door to the next generation
a gene could spread if it caused its bearer to decrease their own fitness in order to increase the reproduction of other bearers of the same gene
Hamilton's Kin selection theory
back door to the next generation
- benefit to recipient X probability that recipient and altruist have the same gene > cost to altruist
= organisms reproductive success + organisms effect on reproduction of its relatives.
altruist behavior is likely to occur when 1 2 3
- 1. cost is low
- 2. benefit is large
- 3. high coefficient of relatedness (r)
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