Evolutionary Forces Drift and Migration Flashcards
melanocytes
produce pigment melanin to be transported to surrounding keratinocytes
keratinocytes
exposed to UV radiation and secrete signals that bind to MC1R molecules on the surface of melanocytes
MC1R location
surface of melanocytes
skin color is determined by (3)
- MC1R allele type: eumelanin or pheomelanin
- amount of melanin produced
- proportions of eumelanin and pheomelanin
MC1R type of receptor
GPCR transmembrane snake
high UV on folate and vitamin D
decrease folate- babies
increase vitamin d
low UV on folate and vitamin D
more folate
less vitamin D-rickets
evolution
change in allele frequencies of a population across generations
type of natural selection refers to
HOW allele frequencies change over time
4 types of natural selection
- directional
- stabilizing
- disruptive/diversifying
- frequency-dependent
directional selection
shifts the mean to a side
stabilizing selection
maintains the middle and acts against extremes
directional selection
finches beaks keep getting larger over time
stabilizing selection with human birth weight
too small-die, too big-complications for mother and child, so needs to be in the middle of the extremes
disruptive selection
acts against the mean phenotype
example of disruptive selection with flies feeding on hawthorn and apple fruits
life cycle for flies that coordinate with a specific tree, not both, would make them more advantageous
frequency-dependent selection
fitness value of a specific trait depends on how common/rare it is in a population
positive frequency dependent selection
more common phenotypes have higher fitness
negative frequency-dependent selection
more rare phenotypes have higher fitness
negative selection can maintain
diversity for phenotypes within a population
positive frequency-dependent selection example with heliconius butterfly
morph that is common is less likely to die because birds know that they are poisonous
if a morph is rare, the bird might not think it is poisonous and it gets killed
negative frequency dependent selection example with grove snails
more common shell types are eaten more often as they become the search image for birds than rare shell types
genetic drift
allele frequencies within a population change by chance alone
genetic drift is an evolutionary force that does not
lead to adaptation
genetic drift sampling error
is higher with a smaller sample
genetic drift random change in allele frequency is due to
imperfect sampling from one generation to the next
factors that cause genetic drift(2)
survival events in nature
random reproduction
genetic drift occurs in all
real populations
genetic drift is especially important in
small populations
consequences of genetic drift (2)
harmful alleles may increase and advantagous ones lost
large effect in small populations
bottleneck effect
size of population is decreased signficantly for at least one generation
founder effect
loss of. genetic variation when a new colony is formed by a very small number of individuals from a larger population
founder effect example
amish–changes allele frequencies
-ellis-van creveld syndrome
gene flow
migration in population genetics from one population to another
gene flow can (2)
add new alleles
change frequencies of existing alleles
gene flow often constrains
local adaptation
gene flow prevents
populations from genetically diversing
factors affecting gene flow(3)
habitat fragmentation-highway bridge
species mobility-plants
location-islands
