Transcript Microevolution

Microevolution
Evolution we can see
Begins
MICROEVOLUTION
• changes in gene frequencies and
phenotypic traits within
populations and species
Hi, I’m the narrator, and I’m here to help explain evolution to you.
And I’m NEMESIS, I am going to question this narrator guy
Previously, evolution evidence was examined and used to explain the world
around us. Ya, I remember all that stuff
We, however, must understand that EVOLUTION is a dynamic process and
continues to occur. What are you talking about, I am not evolving!
You are correct, individuals do not evolve, so you are stuck with the
genetics that were given to you by your mother and father. The
difference, is that populations of species actually are evolving.
Now come on, the animals in the zoo aren’t changing!
Yes, evolution is occurring right now as you read this presentation! The
difference is that you need to look at populations that produce a lot of
generations in a short period of time. Take for example bacteria that
have a doubling time of one hour. These bacteria make a new
generation in only one hour. Now think of how many generations they
can produce in only one day. Ok that’s 24 generations, so what?
Well comparing that to a 35 year generation time for humans, 24
generations would put you back in time to the middle ages.
So how do bacteria apply to me? Wait, I heard people in the middle ages
didn’t take baths
What it means is that evolution can occur much more rapidly for the bacteria
than for your species. Even though you may think you are very different from
bacteria, the same natural forces act upon them, and their genetics, as act upon
all living things. Ex. New bacteria are formed, grow, die and need food, stable
environmental conditions, metabolic chemicals.
Ya, but I don’t see bacteria evolving. What are they turning into, flies?
Well, here is where you are wrong. Bacteria are evolving, its just that they are
evolving in their biochemistry an not their body form. Take for example a
problem that the medical field is experiencing. Every time an antibiotic is
used to kill a population of bacteria, it is possible that one of the members of
that population may have received a mutation in its DNA that causes the
bacteria to survive even when the antibiotic is added. It may be that only one
bacterium survives, but if it does, it will take only 24 hour for that one
bacteria with a doubling time of 1 hour to turn into over 8 million antibiotic
resistant bacteria! Sure wish I made money like that.
Recognition of this problem has resulted in a tightening up of prescription
antibiotics by doctors. It is directly connected to evolution as the incidence
of bacteria with antibiotic resistance has dramatically increased in our
modern world.
I hate my doctor, he never gives me antibiotics when I have the flu!
Newsflash: Antibiotics are useless against a virus like the flu. As a matter of fact,
using antibiotics this way helps more bacteria gain resistance
Hey wait a minute, these are just bacteria, they are prokaryotic, and are a lot
different than our cells. Maybe this only applies to them.
Okay, another microevolution study deals with insect pests in agricultural
fields. It has been noted that specific pesticides applied to crops eventually
become useless at killing the insect pests. Now some might think that it is
because of a problem with the chemical, but it is not. The insect population
is actually evolving resistance to the pesticide. Initially all the insect pests
may have died, but after many times of application, a very small number of
pests survived due to tolerance to the poison. Eventually only these survivors
were reproducing, so the only genes passed on the next generation were
those of pesticide resistance. Due to insect rapid generation time and the
fact that one insect can lay thousands of eggs, the insects responded to the
environmental pesticide. Now, you must understand that the insects are not
doing any thinking, its simply evolution in action where the insect pests
without resistance die, but the pests with resistance thrive. If this were to
happen on a massive scale (the world) over a long time frame the genetics of
the insect pest would change. So smart guy, what do the farmers do with
these superbugs?
Currently, farmers alternate between pesticides so that no insect that
develops resistance one year can offer an advantage to its offspring in the
next year because even though they may be resistant to the current pesticide,
a new one will kill them in that next season. They better keep inventing new
pesticides!
Going back to what we discussed regarding bacteria, some bacteria have
developed multiple drug resistance MDR, and some resistance to all known
antibiotics. If you get sick with these, you have to fight the bacteria off by yourself.
Incidentally, there are limited different antibiotics currently available with very little
research into identifying new ones. Hah, you scientists are pretty short-sighted
What a jab, but for your information, science has to be funded, and interest
from the business and free market economy is centered on profit. From MDR
bacteria to cures for Parkinson’s disease (both rare) little money (comparatively
speaking) is allocated due to little return of profit to the business considering
the great expense of research. So that’s why there are so many cold remedies.
More money for the business with lots of sick people.
STOP STOP STOP JUST WAIT A MINUTE.
You haven’t sold me on this microevolution just yet! What about that
Hardy-Weinberg principle I just learned about. It says that the genetics of
the population does not change with time. You are telling me that it does!
Let me explain. The Hardy-Weinberg principle is indeed correct, but if you recall
there were certain conditions that had to be met before it would apply. All these
conditions are very rarely met in a real world situation Lets take a look at some:
Populations must be large says Hardy-Weinberg. Many populations are
dwindling and are now very small Ex endangered species Many populations are
separated by geography with small populations in isolated areas.
Mate randomly in the population says Hardy-Weinberg.
Some minority cultures historically did not mate into the general population and
this may continue today Or Some animal species show a consistent preference for
a particular body form or behaviour for their mate- sexual selection- leaving other
potential mates out of the reproductive cycle no matter what their attributes
No mutations occur says Hardy-Weinberg We are all exposed to mutations.
Just look at the incidence of skin cancer, a mutation directly connected to the UV
radiation of our cherished sun. The incidence of mutation to gametes, however
is low. ---This is a good thing as most of the time mutations will lead to
problems– but then again, maybe its worth the risk of problems if a mutation
could lead to something like resistance to the HIV virus– Mutations happen
rarely, but occur more in large populations and affect all life on the planet.-- They
are the source of new genetic diversity (new genes created)
No migration says Hardy-Weinberg
We see people enter and leave communities all the time. Animals, plant, they
also are constantly in flux
No natural selection says Hardy-Weinberg. Selection occurs all the time.
Ex. Animals that are slow are the first eaten by predators– eliminating their genes
for the future generations.
Now hopefully you can see what I am getting at. By providing the set of conditions
under which genetic change would not occur, the Hardy–Weinberg principle helps
identify key factors that can cause evolution, a change to the gene pool of a
population or a species. Can I swim in the gene pool?
For our first analysis, let us look at the population issue.
If a population dramatically is decreased in numbers, there is
a good chance that, just by random choosing, many genes
will be lost. Ex If all humans were to die in a nuclear war, but
10 survived they all could have a recessive allele (pretend its
blonde hair) Now all future humans will have only blonde
hair without exception. The population may expand to
millions, yet everyone will have blonde hair. In a less radical
situation, the allele frequency would change. Ex Of the 10
people left, one has brown eyes, the others blue. More blue
eyes would be found in this new population than were found
in the original human population. I like blue-eyed blondes.
GENETIC DRIFT – is the name given to the process
Do you realize that all cheetahs today are virtually identical
genetically ? In technical lingo locus homozygosity or monomorphic
You mean they are all like brothers and sisters? How could that happen?
Related to Genetic Drift is something called the BOTTLENECK EFFECT usually
caused by a dramatic, sometimes temporary, reduction in the size of a population .
I’ve been an a traffic bottleneck before– only a few cars get through! It was very
rapid, just like the one described because it was caused by an accident!
This EVOLUTIONARY BOTTLENECK is similar as only a few individuals survive the
“hard times”
When the population recovers, there are few individuals that contribute genes
to start the future generations. The result is that the species genetics are all
nearly the same.
Have you ever watched this sitcom? Its about seven
stranded castaways trapped on a tropical Island by a
severe storm. I’ve seen it on the retro channel.
Well if these castaways never get off the island no
matter how hard they try (the premise of the show),
they are stuck here to reproduce only with those
who are trapped here. Since it is a small sample,
numerous genetics would be absent that would
normally be found in the general population. The
result of this would be a population different than
the original because of the genetics of the original
castaways. This genetic drift effect is called :
This is called the
FOUNDER EFFECT
For our next analysis, we can look at the random mating scenario
Do you think that your brothers and sisters would be insistent on marrying
someone with the exact same genetics as your preferential mate?
Uh, like I don’t think so
You would expect that in large population, any selection you may require for your
mate would be cancelled out by the selections made by other people like you with
similar genetics. What, you mean everybody won’t marry blue-eyed blondes?
NEWSFLASH-- SEXUAL SELECTION -- NON RANDOM MATING – H-W VIOLATED!!
Sexual selection has resulted in some really obvious genetic preferences.
Ex. Male peacocks –female choose to mate only with flashy feather males-result --males look a lot different than females– sexual dimorphism
Male peacocks are the cool ones! Meet me at the club babe= SEXUAL DIMORPHISM
Sexual dimorphism produces striking differences in physical appearance of males and females
The non random mating may also involve closely related individuals preferentially
mating. In ancient Egypt the pharaohs married their sisters. This would disrupt
H-W if done on a large scale. Even Charles Darwin married his cousin. Mating of
closely related individuals or individuals that isolate themselves to a small
community will have a different genetic makeup than the population at large as a
result of this long term practice. Ex Amish communities I heard it’s legal to marry
your first cousin in Florida
One last point regarding sexual selection. If the males take on these colourful
feather patterns, it makes them stand out and thus more vulnerable to
predation.
Hold on, Sugar! Daddy's got a sweet tooth
tonight!" ...
So even though sexual selection favours inherited traits that enhance mating
success they may also reduce an individual’s chances of survival.
BURP
Next, lets examine the mutation scenario
Mutations are the only source of additional genetic material and new alleles.
That’s okay God, give me the good genes, I’ll pass on the mutations.
Mutations are random changes to the genetic code, and thus they are much
more likely to be neutral or harmful than they are to be beneficial.
See, I was right, no mutations in my genetics please–they could be harmful!
Any mutation that occurs in a gamete has the potential to be passed on to
later generations, and thus enter the gene pool. Maybe wearing my tight
jeans could cause my sperm to mutate—Uh oh.
Evidence suggests that the gene for blue eyes was a result of a mutation.
Okay, I like blue eyes, maybe mutations can be good.
Without mutations, only the brown eye characteristic of humans would exist
NEWSFLASH -- One MUTATION= AN ENTIRELY NEW SPECIES--- POLYPLOIDY
Polyploidy, the most dramatic form of mutation, provides an organism with an
immediate doubling of genetic material. This means that in one generation, it is
different and forms a new species from the original --They are genetically
incompatible. This only occurs in plants and has played a major role in
the evolution of plants. Crazy stuff; Isn’t corn polyploid? I’m eating double DNA
• Harmful mutations occur frequently but they are
selected against and, therefore, these mutant alleles
remain extremely rare.
• Beneficial mutations are rare but they are selected
for and, therefore, these mutant alleles accumulate
over time.
• Lethal mutations are least likely to influence the
evolution of a species (they kill the individual)
Cowabunga
Dudes!
Lets look at migration next.
Hey, that’s like what the Canada goose does.
Not exactly, migration means you move into or out of a population, you just
don’t fly south for the winter. I know, my dad immigrated to Canada.
We know that it is virtually impossible to separate populations, even
though there may be vast boundaries between them. In humans, look at
the example of vast oceans separating continents and isolating various
subpopulations of humans. Humans explored across them, and now the
world population is really one big population, where migration to or from
anywhere is possible. If you think that other forms of life can’t do the
same thing, think again! Ya, I watched that Jurassic Park Movie. You just
can’t stop those dinosaurs
MIGRATE WITH THE FLOW—THE GENE FLOW
Gene flow is the movement of alleles from one population to another
through the movement of individuals or gametes. So go where your flow
may take you, find a mate reproduce and move your genes to some exotic
location, or if you are a homebody, wait until they come to you from
somewhere far away. Either way, you would contribute to gene flow –
changing the genes of the original population.
Lastly, an analysis of natural selection. However, before we
approach this topic we have to understand something about genetic
variations . Hey this is like Darwin’s book “The Origin of Species by
Natural Selection” I actually know something!
NEWSFLASH: DIVERSITY WITHIN A SPECIES-KEY TO GENETIC HEALTH OF POPULATIONS
“I want to luxuriate in the racial deliciousness of our country...We are a nation that
celebrates racial diversity.” Cory Booker - Mayor Newark, New Jersey
Does he want to compliment us or eat us?
The general idea is variation within species (aka diversity) is a great attribute.
Evolutionary speaking, it is a genetic strength – not a weakness. Why and what’s aka?
Diversity within a species better prepares the whole species for survival. Selective
forces can change and traits that may seem advantageous today are not necessarily
adaptive in the future. (aka is also known as) You mean the scrawny guy’s genetics are
important too?
Exactly, If the whole population rid itself of particular genetics (Ex fur) to adopt
those that are preferred because of some new selective pressure (Ex hot
temperatures) it would leave the population vulnerable to being wiped out if
conditions changed (Ex sudden Ice age) Fur keeps you warm but PETA hates it!
NEWSFLASH: HETEROZYGOTES IN A POPULATION MAINTAIN RECESSIVE ALLELES
Now for the
natural selection discussion
It’s about time
Within a population, there is a vast possible number of genes and gene
combinations. These lead to differences that we call variations. In ostrich,
for example, you have some tall, some short, but most are average size. As
you approach either height extreme, there are very few ostrich. Only a few
giants or “tom thumb” sized ostrich. The graph representing the population
would be bell shaped. Kind of like our class average is supposed to be!
You would not expect the population to change if it was in H-W
equilibrium. This bell shaped curve would be constant, but natural
selective pressures could change this population dramatically.
If the ostrich were forced into dense jungle, larger ostrich would be at a
disadvantage (taller individuals hit more branches slowing their speed)
avoiding predatory tigers. This means that ostrich may not reproduce, thus
eliminating its tall genes from the population. Over time and many tiger
meals, the population would shift to a shorter variety ostrich. . I prefer steak.
On the other hand, if the ostrich were placed in open savannah, (where it
actually lives) it would be an advantage to be a fast runner. Taller ostrich with
longer legs would be able to avoid the predators. Small ostrich would become
the meals and small ostrich genes would be lost. The population would shift to
taller ostriches. I heard ostrich are faster runners than humans.
These ostrich examples offer three different
mechanisms of speciation (the creation of new
species)
Hey, where
did they all
go? I’m not
going to
remember
them if
they move
so fast!
Stabilizing selection
Directional selection
Disruptive selection
Stabilizing Selection means that the extremes
on the curve are selected against.
That’s a polite way to say they die
The population
becomes more
uniform in their
genetics.
DIRECTIONAL SELECTION results in a shift of the
population genetics because individuals with more
extreme conditions are favoured.
Sounds kind of like the tall basketball player that gets
all the girls.
The population
phenotype average has
shifted to the right. This
usually occurs when a
population experiences a
change in habitat or
environmental
conditions.
DISRUPTIVE SELECTION favours individuals at
opposite extremes
Disruptive selection
is a significant evolutionary
mechanism for the
formation of distinctive
forms within a population.
Distinctive groups may
eventually become isolated
breeding populations
with separate gene pools.
Hey that means new
species can be created once
they separate!
This usually occurs
when a population
experiences a change
in habitat or
environmental
conditions.
I think I’m starting to understand now. I just have one more thought.
Can’t behaviours, just like body forms be inherited? I know that a lot of
animals can be identified by their mating rituals.
You are correct. Behaviours also can be passed via genetics. It’s a
little different than in humans because we learn behaviours –This is
not something we get from our genetics.
However, in the case of the animal behaviour we are talking about, it
is due to something we call instinct.
That’s all
folks!
The end