Transcript Evolution PowerPoint II

Evolution PowerPoint II
 Sources of
variation and the
results of genetic
variation.
Lesson Goals.
 Students will be able to:
 Describe where the genetic variation in a
species comes from.
 Understand the results of genetic
variation.
 Explain how changing environmental
conditions affect the rate of evolution.
 Predict what will happen to a species
that cannot adapt to a changing
environment.
Sources of variation
 There are two possible
sources of variation within
a population.
 1. Mutation: A mutation
is the change in the base
sequence of DNA.
 Mutations that occur in the
gametes (sex cells) can be
passed on to the offspring
in sexual reproducing
organisms.
 Nearly all mutations are
harmful.
Beneficial mutations
 While the majority of mutations are
not beneficial, sometimes random
changes in the DNA give an individual
a competitive advantage.
 An example of a beneficial mutation
occurred in peppered moths.
 Lets take a look at what happened
with these now famous moths.
Peppered moths
 Before the industrial revolution, the
dominant color of the peppered moth was a
very light color.
 This allowed them to blend in with the tree
trunks, which were also light colored.
 Pollution caused the trees to be covered
with soot, darkening them and making the
white moth stand out and become much
more vulnerable to predation.
 A mutation for dark colored moths which
once had a low adaptive value now had a
much higher one.
Genetic shuffling
 In sexually reproducing species, the far
greater source of variation is comes from
the shuffling of genes during meiosis and
fertilization.
 Asexual reproducing species lack this
source of variation in virtually all cases.
 Some unicellular organisms DO exchange
genetic material with each other, but they
do not need to in order to reproduce.
 This process is called conjugation.
Evidence for evolution.
 There are several different sources of
evidence for evolution.
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Fossil Records
Homologous Structures
DNA similarities
Genetic changes within species
Fossils
 Remains of animals and plants found in
sedimentary rock deposits give us an
indisputable record of past changes through
time. This evidence attests to the fact that
there has been a tremendous variety of
living things. Some extinct species had
traits that were transitional between major
groups of organisms. Their existence
confirms that species are not fixed but can
evolve into other species over time.
Homologous structures
 Many groups of species share the same
types of body structures because they
inherited them from a common ancestor
that had them. This is the case with the
vertebrates , which are the animals that
have internal skeletons. The arms of
humans, the forelegs of dogs and cats, the
wings of birds, and the flippers of whales
and seals all have the same types of bones
(humerus, radius, and ulna) because they
have retained these traits of their shared
common ancient vertebrate ancestor.
DNA
 All of the tens of thousands of types of
proteins in living things are made of only
20 kinds of amino acids. Despite the great
diversity of life on our planet, the simple
language of the DNA code is the same for
all living things. This is evidence of the
fundamental molecular unity of life.
 The DNA code is most similar between
closely related species. Humans and
Chimpanzees share over 98% of their
genes.
Genetic change within a species
 This process of natural selection resulting
in evolution can be easily demonstrated
over a 24 hour period in a laboratory Petri
dish of bacteria living in a nutrient
medium. When a lethal dose of antibiotic
is added, there will be a mass dieoff. However, a few of the bacteria
usually are immune and survive. The
next generation is mostly immune
because they have inherited immunity
from the survivors.
Video
 Isn't evolution just a theory?