Download How Does a Population in “Hardy-Weinberg equilibrium” change

How Does a Population in “Hardy-Weinberg equilibrium” change ?
(687)....or.......How does a population evolve ?
Rattlesnake example...page 687
Mechanisms/Processes that drive change include......
1. Mutations :
2.
-
might create NEW alleles for a trait
-
might provide an advantage to organisms carrying it, so they
reproduce more and their alleles become more common in the
population
Ex. Bacterial resistance to antibiotics
-
provide more diversity to face environmental changes, what
wasn’t an advantage before may become an advantage later
Ex. Water fleas (“Daphnia”) mutated allele enables
survival when water warms to 25 or 30 degrees, others die
Genetic Drift :
happens in really small populations....how common each allele is
(it’s “frequency”) changes a lot by chance alone...
2 scenarios making this happen....
Bottleneck effect its less likely all of the alleles in the parent population will
show up in the next generation. ( not all reproduce ).
Some alleles become common quickly, while others are
lost (drift)...less variation in the next generation
Ex.
Northern elephant seals hunted down to 20
animals in the 1800s, now bounced back to
30 000....but studies of 24 loci show NO
variation.
Whooping cranes in NWT : 12 to 177
Endangered species with really small
populations
Founder effect A small number of organisms colonize a new
environment. Their gene pool doesn’t contain all the
alleles of the parent population. (Drift)
3.
Gene Flow :
new alleles are brought into a gene pool, or some genes leave
if there’s a significant amount of gene flow between two
populations, the gene pool blends into one over time, and
combined with selection, some diversity is lost
Ex. Our own population ?
4.
Non-Random Mating :
inbreeding creates more homozygous organisms
5.
-
ex. self pollination in plants, or isolated populations
-
assortative mating, selecting a mate that has a similar phenotype
as you, less diversity over repeated breedings
ex.
Dog breeding....may lead to increase in frequency
of conditions like hip dysplasia
Natural Selection :
- 3 types........
Stabilizing selection -
the environment favors the “in the middle”
phenotypes, and selects out the extremes
Ex.
Human birth weight
Directional selection -
one extreme phenotype is selected over all
others
Ex.
Small forest dwelling prehistoric
horse species producing large open
grassland horse species
Fat on penguins
Disruptive selection -
6.
the extreme phenotypes at both ends of a
population are favored, the “in the middle”
phenotypes are removed
Sexual Selection :
smaller motile sperm (increased numbers) and enlarged nonmotile egg , creating competition between males that go looking
for eggs. Leads to lots of diverse ways of attracting mates and
species sexual behavior.
Ex.
Different bird plumage between genders
(Sexual dimorphism)
Courtship displays / rituals
How Species Form...”Speciation”
(page 708)
A species is a group of related creatures capable of breeding to produce fertile offspring.
New species may form by way of two main pathways....both due to natural selection working on a
pop’n....
Transformation the build up of small changes over time
Divergence A new species forms from a parent species that continues to exist.
To remain a distinct species, a pop’n must have barriers to prevent interbreeding, like...
Geographical barriers -
a topographic feature keeps pop’ns separate....like a river or
canyon ( allopatric speciation )
Biological barriers -
Keep reproduction separate, even when living in the same
area, like...
Pre-Zygotic Barriers (prevent mating or egg fertilization)
Behavioral isolation-
songs, dances, pheromones are
species specific
Habitat isolation-
even though they live together,
habitat preferences mean
different species encounter
each other less often
Temporal isolation-
timing barriers ( day, season,
year of mating varies)
Mechanical isolation-
your gear doesn’t mesh
Gametic isolation-
sperm / egg incompatible
Post-zygotic Barriers -
(Prevents
hybrid zygotes from
reproducing......)
Hybrid inviability, sterility, or breakdown
Processes Giving Rise to Species :
Sympatric speciation -
reproductive isolation.
Ex. Plants with unique chromosomal structure,
animals having non-random mating
Polyploidy in offspring -
will only successfully mate with another polyploid,
new species that can’t breed with parent organism
Allopatric speciation -
population split into groups by geography
Adaptive radiation, or divergent evolution a species colonizes new areas different enough for N.S. to form a variety of species
from a common ancestor. Ex. Galapagos finches
Convergent evolution Two unrelated species eventually turn out similarly in similar environments. Ex.
Bird and bat flight
Coevolution Two species interact to control the evolution of the other, like plants and pollinators,
predators and prey, parasites and hosts.
The speed of evolution :
2 theories :
gradualism and punctuated equilibrium
Gradualism slow accumulated changes, not supported as much in the fossil record.
Punctuated equilibrium (Gould - Eldridge hypothesis)
Sudden bursts of speciation ( < 50 000 yrs) interrupt long periods of time
where species seem relatively unchanged.
Theories on the Origins of Life :
Chemical Evolution -
pros/cons, page 730
( the Haldane - Oparin hypothesis )
Inorganic chemicals could, under the right atmospheric conditions, become
rearranged to make organic chemicals.
Tested by Stanley Miller in 1953
methane, ammonia, hydrogen, and water inside a setup, sparks to mimic
lightning...after a week, organic molecules present....including amino acids
This is not life, but more tests show nucleotides and RNA form too. Self
replicating molecules must have existed before any life forms.
The Panspermia theory :
life originated elsewhere, and traveled to Earth, introduced by meteors, or by
other beings.
The Gaia Theory :
chemical evolution first, then the Earth living as a large organism controlling
populations and maintaining homeostasis....James Lovelock...1960's
Intelligent Design Theory :
A supernatural being created all life, since life and all of its processes are too
complex to be the result of random chance over long periods of time.
( Creationism )
Serial Endosymbiosis Theory ( SET ) :
(The Lynn Margulis hypothesis)
Eukaryotic cells included into their structure smaller free living bacteria like
life forms, ( aerobic bacteria to mitochondria, photosynthetic bacteria to
chloroplasts ), which allowed them to survive in more environments.