Download Hardy- Weinberg Principle A. conditions for genetic equilibrium

Evolution
Also, many plants, and some animals, form hybrids in nature.
Hooded crows and carrion crows look different, and
largely mate within their own groups—but in some areas,
they hybridize.
Should they be considered the same species or separate species?
• If two lineages of oak look quite different,
but occasionally form hybrids with each
other, should we count them as different
species? There are lots of other places
where the boundary of a species is
blurred. It’s not so surprising that these
blurry places exist—after all, the idea of a
species is something that we humans
invented for our own convenience!
gene pool - collection of genes for
all traits in a population
contains all the alleles
• allele frequency-
• Genetic equilibrium -
How do the three terms
relate???????
Hardy- Weinberg Principle
A. conditions for genetic
equilibrium
page 302 list the five
• The Hardy-Weinberg equation is a simple
but powerful tool for predicting the
allele frequencies within a population.
Its prediction of genetic equilibrium or no
frequency change under a specific set of
conditions also serves as strong evidence
for microevolution. As long as a population
does not meet all the prerequisite
conditions for genetic equilibrium, allele
frequencies must change over time, and
this is the primary process of evolution.
Mutations
Sickle cell anemia is the result of a point mutation,
a change in just one nucleotide
in the gene for hemoglobin.
This mutation causes the hemoglobin in red blood cells
to distort to a sickle shape when deoxygenated.
The sickle-shaped blood cells clog in the capillaries,
cutting off circulation.
Cancer usually results from a series of
mutations within a single cell. Often, a faulty,
damaged, or missing p53 gene is to blame.
The p53 gene makes a protein that stops mutated
cells from dividing. Without this protein, cells divide
unchecked and become tumors
Genetics of Huntington’s disease
Caused by a “stutter” or repeat of three bases, CAG,
that are normally in a repeat of 11-29 copies;
the mutation is an increase to 37-100 copies
“Good Mutations”
• Scientists believe that the reason for their survival was a genetic
mutation found in descendents of the survivors. The gene is called
CCR5-delta 32, or Delta 32 for short. Delta 32 is a gene that codes
for a protein on the surface of white blood cells which acts as a
receptor for other molecules involved in inflammation.
Essentially, since the CCR5 Delta 32's receptor's are "turned off", it
makes a person resistant or immune to certain viruses because they
cannot latch onto the receptors. People who have two copies of the
Delta 32 mutation were virtually immune to The Black Death, one
from each parent. Those who only had one copy of the mutated
gene were resistant to it. The Delta 32 mutation is more common in
people of Northern European descent. Smallpox - not The Black
Plague - is thought to be the reason for this gene mutation.
Smallpox epidemics were common in Europe and so some people
developed this mutation.
• Since the CCR5 Delta 32's receptor's are
"turned off", it makes a person resistant or
immune to certain viruses because they
cannot latch onto the receptors.
Migration
• Genetic drift affects the genetic makeup
of the population but, unlike natural
selection, through an entirely random
process.
a.An ant gets stepped on.
b.A rabbit gets swept up by a tornado.
c.An elephant drinks up a protozoa living in a puddle.
d.A plane crashes killing a Nobel Laureate.
Bottleneck effect – sudden events that
drastically reduce the population size.
Example: natural disasters, chance event
*survivors are usually not selected
based upon genotype but rather by chance.
Effects gene pool????
Founder effect
A small group of females is separated
from the original population and establishes
a new population.
( isolated from original & caused by chance)
Birds from mainland area move to an isolated island
far out to sea
Example: Many of the bird species
found on Galapagos Islands
Non random mating
Natural Selection
Natural selection at work
Orchids fool wasps into
"mating" with them.
Katydids have
camouflage to look like
leaves.
Non-poisonous king snakes mimic
poisonous coral snakes
The creosote bush is a desert-dwelling plant that produces toxins that
prevent other plants from growing nearby, thus reducing competition for
nutrients and water.
Artificial selection
Long before Darwin and Wallace, farmers
and breeders were using the idea of
selection to cause major changes in the
features of their plants and animals over
the course of decades. Farmers and
breeders allowed only the plants and
animals with desirable characteristics to
reproduce, causing the evolution of farm stock. This process is called
artificial selection because people (instead of nature) select
which organisms get to reproduce.
As shown below, farmers have cultivated numerous popular
crops from the wild mustard, by artificially selecting for certain
attributes.
• Artificial selection is the process of
changing the characteristics of animals by
artificial means. For example, animal
breeders, are often able to change the
characteristics of domestic animals by
selecting for reproduction those individuals
with the most desirable qualities such as
speed in racehorses, milk production in
cows, trail scenting in dogs.
Golden saddleback
only about 150 years old.
'barrel' more rounded
than in other breeds
• The Labradoodle was first deliberately
bred in 1989, when Australian breeder
Wally Conron first crossed the Labrador
Retriever and Standard Poodle for
Guide Dogs Victoria. His aim was to
combine the low-shedding coat of the
Poodle with the gentleness and
trainability of the Labrador, and to
provide a Guide Dog suitable for people
with allergies to fur and dander. Guide
Dogs Victoria continue to breed
Labradoodles today and Labradoodles
are now often used around the world as
Guide, Assistance, and Therapy Dogsas
well as being popular family dogs.
Disruption of the genetic
equilibrium leads to evolution
Some evolutionary changes
One example is vestigial structures.
A vestigial structure is a feature that was an adaptation for
the organism's ancestor, but that evolved to be non-functional
because the organism's environment changed.
Fish species that live in completely dark caves have vestigial, nonfunctional eyes. When their sighted ancestors ended up living in caves,
there was no longer any natural selection that maintained the function of
the fishes' eyes. So, fish with better sight no longer out-competed fish with
worse sight. Today, these fish still have eyes — but they are not functional
and are not an adaptation; they are just the by-products of the fishes'
evolutionary history.
homologous characters — characters in different organisms
that are similar because they were inherited from a common
ancestor from a common ancestor that also had that character.
Birds, bats, mice, and crocodiles all have four limbs.
Sharks and bony fish do not.
The ancestor of tetrapods evolved four limbs,
and its descendents have inherited that
feature — so the presence of four limbs is a homology
.
Biologists use a few criteria to help them decide
whether a shared morphological character
(such as the presence of four limbs) is likely to be a homology
Same basic structure
The same bones (though differently shaped) support the limbs of mice and crocodiles.
In the illustration of forelimbs at left, homologous bones are colored alike.
Bird and bat wings are analogous — that is, they have separate
evolutionary origins, but are superficially similar because they
evolved to serve the same function.
Analogies are the result of convergent evolution.
Interestingly, though bird and bat wings are analogous as wings,
as forelimbs they are homologous. Birds and bats did
not inherit wings from a common ancestor with wings,
but they did inherit forelimbs from a common ancestor
with forelimbs.
Formation of Species
• Read article
Geographic isolation
The Satin bowerbird builds a channel
between upright sticks, and decorates with
bright blue objects
MacGregor’s Bowerbird builds a tall tower of
sticks and decorates with bits of charcoal.
The evolution of different mating location, mating time, or mating rituals:
Genetically-based changes to these aspects of mating could
complete the process of reproductive isolation and speciation.
For example, bowerbirds (shown above) construct elaborate bowers
and decorate them with different colors in order to woo females.
If two incipient species evolved differences in this mating ritual,
it might permanently isolate them and complete the process of speciation.
pre zygotic


different mating times
different mating call
post zygotic
offspring die early
healthy but not fertile
Types of evolution:
Coevolution
The term coevolution is used to describe cases where two
(or more) species reciprocally affect each other's evolution. So for
example, an evolutionary change in the morphology of a plant,
might affect the morphology of an herbivore that eats the plant,
which in turn might affect the evolution of the plant,
which might affect the evolution of the herbivore...and so on.
• Hummingbirds and ornithophilous flowers have
evolved to form a mutualistic relationship. It is
prevalent in the bird’s biology as well as in the
flower’s. Hummingbird flowers have nectar
chemistry associated with the bird’s diet. Their
color and morphology also coincide with the
bird’s vision and morphology. The blooming
times of these ornithophilous flowers have also
been found to coincide with hummingbirds'
breeding seasons
This system is probably the
product of coevolution: the
plants would not have
evolved hollow thorns or
nectar pores unless their
evolution had been
affected by the ants, and
the ants would not have
evolved herbivore defense
behaviors unless their
evolution had been
affected by the plants.
Convergent evolution
Convergent evolution represents a phenomenon when two
distinct species with differing ancestries evolve to display
similar physical features.
Traits arising through convergent evolution are termed
analogous structures, in contrast to homologous
structures, which have a common origin
Convergent Evolution
A small mantispid and a preying mantis. Although they differ greatly in size, these two insects are
remarkably similar in appearance. They both have triangular heads with large eyes and a pair of raptorial
(grasping) front legs. Their other two pairs of legs are used for walking. They belong to two very different
insect orders. Although mantids were once placed in the order Orthoptera along with grasshoppers,
crickets and cockroaches, they are now placed in the separate order Mantodea. Mantispids belong to the
order Neuroptera, along with lacewings, snakeflies and antlions. Their remarkable adaptive similarity is
an example of convergent evolution.
Divergent Evolution
• group from a specific population develops
into a new species. In order to adapt to
various environmental conditions.
• Divergent evolution is the process of two or more related
species becoming more and more dissimilar. The red fox
and the kit fox provide and example of two species that
have undergone divergent evolution. The red fox lives in
mixed farmlands and forests, where its red color helps it
blend in with surrounding trees. The kit fox lives on the
plains and in the deserts, where its sandy color helps
conceal it from prey and predators. The ears of the kit
fox are larger than those of the red fox. The kit fox's
large ears are an adaptation to its desert environment.
The enlarged surface area of its ears helps the fox get
rid of excess body heat. Similarities in structure indicate
that the red fox and the kit fox had a common ancestor.
As they adapted to different environments, the
appearance of the two species diverged.
Kit Fox
Red fox
• What can speed up divergent evolution?
The next slides are cladograms
Look up the definition