Transcript Mutations - 7sciencewithmcmillan

Artificial Selection
& Natural Selection
What is Artificial Selection?
Artificial selection is the process of breeding plants and
animals for particular traits. It is also called “selective
breeding”.
This selection process is "artificial" when human
preferences for specific traits have a significant effect on
the changes in a particular population or species.
Advantages of Selective Breeding
Selective breeding tries to establish certain traits that
animals will pass to the next generation.
These are traits that humans find desirable in
domesticated species such as disease resistance,
strength, calmness, more lean meat, endurance, etc.
Disadvantages of Selective Breeding
Breeding from too small a gene pool can lead to the passing on of
undesirable characteristics or even a collapse of a breed
population due to inbreeding.
Breeding for only one trait, over all others, can cause associated
problems.
Example 1: Certain roosters bred for fast growth or heavy muscles did
not know how to perform the typical rooster courtship dance. The
dance bonds the roosters to the hens. No mating dance led the
roosters to kill the hens after reproducing with them.
Example 2: Many “purebred” dog breeds inherit physical problems
that are common to their breed (hip displasia in German Shepherds,
respiratory problems in Pugs, etc.)
What is Natural Selection?
Natural selection is the process organisms better
adapted to their environment tend to survive and
produce more offspring.
This is observable.
“The Struggle for Existnce” and
“Survival of the Fittest”
The Struggle for Existence: members of each species
have to compete for food, shelter, and other life
necessities.
Survival of the Fittest: Some individuals with certain
traits better suited for the environment and will survive
to reproduce the next generation.
What is the difference between
natural selection & mutations?
Mutation= A random change
in an organism’s DNA.
Can be inherited – passed
down from a parent to their
offspring
Can be caused by
carcinogens (cancer causing
agents in the environment)
EXTREMELY RARE!
Mutation = a random change in an organism’s DNA
Most mutations are NEGATIVE
(harmful)
Negative mutations hurt the
organism’s chances for
survival
Mutated blood cell
(person with sickle cell
anemia)
Normal red blood cell
Some mutations are NEUTRAL
(not harmful, not helpful)
Neutral mutations do not affect the organism’s survival (the
mutation does not help or hurt the organism)
Very few mutations are POSITIVE
(helpful)
Helpful mutations provide an advantage which helps the
organism survive
In bacteria, a wide range of mutations can be shown to
provide a beneficial phenotype to the cell. These benefits are
often of sufficient phenotypic affect that they can undergo
strong positive selection. But the benefits are generally
temporary and limited. Some common examples of beneficial
mutations are those involved in bacterial antibiotic
resistance. These mutations potentially enable the bacterium
to survive exposure to various antibiotics, but the resistance
results from loss or reduction of pre-existing activities such as
enzymatic, regulatory, or transport systems.
Most mutations harmful
Some mutations can have no effect
(NEUTRAL)
Very few mutations are helpful
Darwin’s Theory of Evolution
by Natural Selection
The Theory of Evolution is the process
by which different kinds of living
organisms are thought to have
developed and changed from earlier
forms during the history of the earth.
Microevolution (natural selection;
changes within species)
Macroevolution (one species changes to
another species)
A theory is an idea or set of ideas that is
intended to explain facts or events.
Darwin’s Reasoning
Observed that a population can outgrow its resources which would lead
to competition for existence among offspring.
Observed that certain variations are more likely to survive and
reproduce (“natural selection”).
Assumed that the earth was very old.
Assumed that small changes over time can eventually lead to larger
changes over a long enough period of time (one species changes into
something different = “evolution”).
Evolutionary Terminology:
Descent with Modification: each living organism has descended, with
changes from other species over time.
Common Descent: all organisms are come from a single common ancestor
Common Descent
& Descent with Modification
Giraffe Theory
= An evolutionary explanation why giraffes have long necks.
•
Giraffes with longer necks had an advantage. They could reach leaves other
giraffes could not. Therefore, the long-necked giraffes were more likely to
survive and reproduce (greater fitness_.
These giraffes passed the long-neck trait to their offspring. Each generation,
the population contained more long-necked giraffes. Eventually, all giraffes
had long necks.
Giraffe Theory – HOWEVER…
•
Female giraffe necks are 2 feet shorter
than males. If longer necks were needed
to reach above the forage line, then
females would have starved to death.
•
NO EVIDENCE in the fossil record of
gradual increase the neck.
•
Giraffe “adaptational package”:
exceptionally large heart (3 x’s man’s
heart); blood pressure control; oversized
lungs; respiratory rate 1/3 of humans;
capillaries are very internal and 1/3 the
size of humans.
“Darwin’s Finches”
Darwin's finches are 13-14 different species of finches living on the Galapagos
Islands (considered an icon of evolution).
Each island has its own variety of finch, with the most importance difference
being the size and shape of their beaks used for different diets and lifestyles.
“Darwin’s Finches”
Some had large beaks used for cracking nuts and seeds, while others had slender
beaks suited for catching insects etc.
The explanation for this given by Darwin was that all the finches on the islands
came from one original pair of finches, and that natural selection is responsible
for the differences.
Because of the variations in the finches he inferred that all species on earth had
evolved from this process over billions of years.
Current Research
Researchers are now discovering that organisms can robustly adapt to
different ecological niches without major changes in their DNA
sequence.
A team of Princeton scientists have won a prestigious award for 20 years
of study of the finch's beaks. Just what was found?
The two scholars, Drs. Peter and Rosemary Grant observed how, under
drought (dry) conditions, birds with larger beaks were better adapted
than others, thus their numbers increased. But this trend reversed
when the conditions reversed and it became wet again. Furthermore, in
times of drought, the normally separate species were observed to crossbreed. They are related after all.
But is this really evolution? Even after the changes there is still the same
array of beak sizes and shapes. This is variation and adaptation, not
evolution. Actually, de-evolution has occurred; the observation is that
there are larger groupings of species into what may be more
reminiscent of the original kind. INTERPRETATION OF THE DATA IS KEY.