Transcript Bottleneck effect - Madeira City Schools

A. What is a species?
1. From Latin word for “kind” or “appearance”
2. There are different concepts for which species is defined.
The most accepted is the “biological species concept”
a. a species is a population or group of populations whose
members have the potential to interbreed (mate) in
nature and produce fertile offspring.
3. Reproductive isolation – the existence of biological
barriers that do not allow two species to produce viable,
fertile, offspring.
Prezygotic barriers – can’t mate or fertilization can’t happen
a. Habitat isolation – rarely encounter one another
b. Temporal isolation – breed at different times
c. Behavioral isolation – courtship rituals not understood
d. Mechanical isolation – mating occurs, but structurally they
don’t “fit”
e. Gametic isolation – sperm does not recognize egg or can’t
survive in other species environment
Postzygotic barriers – hybrid can’t develop into viable, fertile adult
a. Reduced hybrid viability – development incomplete
b. Reduced hybrid fertility – hybrid is sterile
c. Hybrid breakdown – offspring weak or not viable
B. Causes for a population to evolve
1. Genetic drift = change in gene pool of a small population
due to chance.
a. Bottleneck effect = genetic drift resulting from an event
that drastically reduces population size
b. Founder effect = random change in the gene pool that
occurs in a small colony of a population
Example: “Founding population” of an island
2. Gene flow = gain or loss of alleles from a population by
the movement of individuals or gametes
a. migration of individuals into (immigration) or out of
(emigration) an area.
b. plant pollen
3. Mutation = random change in an organism’s DNA that
creates a new allele
a. raw material for evolution
4. Nonrandom mating = selecting mates (“sexual selection”)
rather than by chance
5. Natural Selection = differential success in reproduction
C. Speciation can take place with or
without geographic separation
1. Allopatric Speciation – “Allo”=
other; “patra”= homeland
a. gene flow is interrupted when a
population is divided into
geographically isolated
subpopulations.
b. population can be divided by
river, mountains, lake water
may decrease causing two
lakes
2. Sympatric Speciation – “Same
Country”
a. How can reproductive barriers
between populations evolve when
the members remain in contact with
each other?
b. Switching habitat, food source, or
other resource not used by the
parent population
c. When two species interbreed and
produce a hybrid that goes through
asexual reproduction which can
lead to mutations that make them
fertile with other hybrids and not the
parent.
D. Adaptive Radiation – the evolution of
many diversely adapted species from a
common ancestor.
1. Ancestor was introduced to various new
environmental opportunities and challenges.
2. Natural Selection caused different traits to be
selected for based on environment and
challenges ancestor faced.