Download Natural selection (and evolution)

Natural selection and
Evolution
What is this all about?
video
Traits
• Traits are passed from one
generation to the next
• That means that all the
information to produce all of
your traits was contained within
the single cell that was you when
you were conceived.
• What determines your traits?
Proteins
• Proteins determine our traits
• Each protein is a sequence of amino
acids. Which amino acids and in which
order determines the structure and
function of the protein.
• How are proteins produced?
Hemoglobin: a protein that is 146 amino acids long
Val
His
Leu
Thr
Pro
Glu
Lys
… 139 more
DNA
• DNA is the blueprint or recipe book
for making proteins (and therefore
traits). This is what is passed on
from one generation to the next.
• How does DNA code for proteins,
thus traits?
DNA
Proteins
Traits
DNA is arranged as a double helix
•It is composed of four types of nucleotides:
A  Adenine
T  Thymine
G  Guanine
C  Cytosine
From this four letter alphabet different amino acids are
specified.
Nucleotides
• DNA is composed of nucleotides: the
information part of the DNA. There are only
4 types of nucleotides in DNA: A, T, G, and C
A = adenine
T = thymine
G = guanine
C = cytosine
• From this four letter alphabet different
amino acids are specified
More on DNA
•
•
•
•
•
•
A-T
A-T
T-A
C-G
G-C
T-A
every three nucleotides
(codon) codes for one of the
20 amino acids
(and there are 1000s
of nucleotides in a
strand of DNA)
There are also sequences of 3 nucleotides that specify
where to start and where to stop reading along the DNA to
make the protein. This is called translation.
THE GENETIC CODE
Thymine (T) is replaced with Uracil (U) in messenger RNA.
More on DNA
•
•
•
•
•
•
A-T
A-T
T-A
C-G
G-C
T-A
So another definition
of DNA is a sequence
of 1000s of nucleotides
in a double strand that
is the recipe for amino
acids and therefore proteins
Three processes
• REPLICATION
– Synthesis of two
DNA molecules from
DNA template
• TRANSCRIPTION
– Synthesis of RNA
molecule from DNA
template
• TRANSLATION
– Synthesis of a
protein from RNA
template
Genes are translated into proteins
based on a triplet code
Transcription
Codon =
3 bases
Translation
Protein =
many amino
acids strung
together
Amino acid
• DNA is composed of
nucleotides
Recap
– There are only 4 types
of nucleotides
• Every 3 nucleotides
codes for an amino acid
– There are 20 different
amino acids
• Strands of amino acids
form proteins
• Proteins are
responsible for traits
and adaptations…
Video on DNA translation
Video2 on DNA translation
Chromosomes
• So what is a chromosome?
Chromosomes
• So what is a chromosome?
– Strands of DNA, all tightly wrapped up
and existing in a cell’s nucleus
• [Humans have 46 chromosomes, 23
from each parent?]
Genes
• So what is a gene?
Genes are a particular segment of DNA,
that code for a protein (usually).
Junk DNA
Genes
• So what is a gene?
– A section of DNA that encodes
information for building a protein (or
RNA molecule)
– Each chromosome can have thousands of
genes on it.
Mutations
• What is a mutation?
Mutations
• What is a mutation?
– A change in the sequence of nucleotides in a gene.
– They are random, caused by
• Chemicals, radiation, copying errors
– They change the protein that is specified
• May be beneficial, neutral, harmful, or lethal
Alleles are variants of genes
Sickle cell disease
• Occurs due to a mutation in the gene that codes
for the hemoglobin protein. protein that carries
oxygen in red blood cells.
• Causes the normally round red blood cell to
change into a sickle shape that no longer carries
oxygen as well. This can be lethal. Red blood cells
of affected individuals distort in shape, break
down or clog blood vessels and cause pain, poor
circulation, etc
Val
His
Leu
Thr
Pro
Glu
Lys
… 139 more
Val
His
Leu
Thr
Pro
Val
Lys
… 139 more
Sickle cell disease
• Alleles: different versions of genes.
–
–
–
–
Sickle cell allele (h)
“normal” allele (H)
Sickle Cell Anemia (hh): often lethal
Sickle Cell Trait (Hh): symptoms vary,
usually very little effects.
Mom
H
Dad
h
H
h
HH Hh
Hh hh
Sickle cell disease
• Is having the sickle cell allele good or
bad?
Sickle cell disease
• Is having the sickle cell allele good or
bad?
– It depends on the environment!!
– The sickle cell allele confers genetic
resistance to malaria, one of the biggest
killers of infants in areas with malaria.
• So, where do you think you find
populations with the highest incidence
of the sickle cell allele? Malaria areas
PBS Video
Some more genetic diseases mapped
List
Gene pool
• Gene Pool: all of the alleles and their
proportions in a population.
Gene pool
• Gene pools change over time.
80%
20%
Environmental Change –
Pesticide introduced
0%
100%
Resistant Gene
Gene pool
• A change in a gene pool over time is
called what?
Evolution
• Genetic Evolution: a change in a gene pool
– Note: this operates at the population level!
Another definition is a genetic change in a
population.
Mechanisms of evolution
• What causes gene pools to change?
Mechanisms of evolution
• What causes gene pools to change over time?
• 1. Mutations: produce new alleles and new
genes.
–
–
–
–
are random
cannot be predicted ahead of time
create genetic variety
may be beneficial, neutral, or harmful to the
individuals that inherit them
Mechanisms of evolution
2. Migration (immigration/emigration).
– Technical term is gene flow.
– The movement of alleles between
populations as a result of movement of
individuals from one population to another.
Mechanisms of evolution
3. Chance: when chance, rather than traits
determine reproductive success. Example:
disaster that kills part of a population.
Small populations are more susceptible to
big evolutionary change due to chance.
Technical term is Genetic Drift.
Mechanisms of evolution
• 4. Natural Selection. When traits
determine reproductive success; traits in
more reproductively successful individuals
get passed on more into the next
generation.
Natural Selection
• Natural Selection. Alleles that confer
“success” are more likely to be passed on
to future generations and will increase
their % relative to other alleles over time.
Technical term for “success” is
differential reproductive success.
Example of Natural Selection
Resistant Allele
• Gene pools change over time.
Alleles
80%
20%
Environmental Change –
Pesticide introduced
0%
100%
Non-Resistant
Allele
Example of natural selection
• Beetles and pesticide resistance
– The resistant and non-resistant alleles were due to past
mutations that created genetic variety in the beetles
but were neutral until now (pesticide spraying time).
– The pesticide acted as a new environmental selection
pressure that selected for the resistant allele.
– This selection pressure, causing individuals with the
resistant allele to out-survive and out-reproduce
individuals without the resistant allele, resulting in an
increase in individuals with the resistant allele in the
next generation.
Natural Selection
http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_14
Natural selection flowchart
New Genes
Random
Recombination
New combinations of existing genes
Sexual reproduction
Genetic Variability—Gene Pool
Current mix of genes in population
Environmental Selection Pressures
Reproduced
Genes
Mutation
Examples: climate, predation, mate selection
Differential Survival
Differential Reproduction
Some genes and gene
combinations help the individual
survive better than other
individuals.
Some genes and gene combinations
help the individual reproduce better
than other individuals
Natural selection flowchart
• Mutation and recombination create
genetic variety in gene pool of a
population.
• Mutations: create new alleles/genes.
• Recombination: sexual reproduction
mixes alleles and creates new
combinations of alleles.
Variation
arises from
Mutation:
new genes
Sexual Recombination:
new gene combinations
Natural selection flowchart
• Environmental selection pressure:
affects the survival and reproduction
of individuals in a population
differently (think back to the
beetles)
Natural selection flowchart
• Environmental selection pressure
leads to differential survival and
differential reproduction of
individuals with more successful
alleles. This is passed on to future
generations and changes the gene
pool through time.
“evolution: survival of the
fittest”
• Isn’t that what we were taught in
school? Well, its wrong.
• This is an example of science being
misinterpreted by the public.
“evolution: survival of the
fittest”
• What does fittest mean?
– To a biologist?
– To the public?
“evolution: survival of the
fittest”
• What does fittest mean?
– To a biologist?
• = differential reproductive success
– To the public?
• = biggest, strongest, ….
“evolution: survival of the
fittest”
• What does fittest mean?
– To a biologist?
• = differential reproductive success
– To the public?
• = biggest, strongest, ….
• ALL that really matters is whether or
not your genes are passed on to
future generations ….
Artificial Selection
Types of evolution
• 1. Divergent evolution
• 2. Convergent evolution
• 3. Co-evolution
Divergent Evolution
• 1. Divergent evolution
– Two different populations of a species that
experience different selection pressures may
as a result become genetically different from
one another
• Once in a very great while, the two populations will
become so different that they cannot reproduce
together anymore (this then becomes speciation).
Divergent Evolution
Divergent Evolution
Divergent Evolution
Species and Speciation
Review: Definition of Species:
One or more populations whose members
actually or potentially interbreed under
natural conditions and that are
reproductively isolated from other such groups.
Divergent Evolution
http://www.biology-online.org/images/darwin_finches.jpg
Divergent Evolution
Convergent Evolution
• 2. Convergent evolution
– Start with two very different species;
they experience similar selection
pressures and through time come to look
and/or behave similarly.
Convergent Evolution
Fish
Reptile
Mammal
What is the
similar
selection
pressure?
Convergent Evolution
Convergent Evolution
What is the
similar
selection
pressure?
http://www.votawphotography.com
/photo/Animals/animals.htm
Speed to catch prey
(cheetah) and speed
to win races and be
bred.
http://www.hundekosmos.de/images/greyhound_517.jpg
Convergent Evolution
Placental
Mammals
Marsupial
Mammals
Convergent Evolution
“Ant eaters” of the world
Convergent Evolution
Many plants look like cacti because they also have
evolved to store and defend water but they are not
cacti – for example, the ocotillo is not a cactus, it is a
shrub in a different plant family.
Types of evolution
• 3. Co-evolution
– Two species that interact with each other
(predator/prey; mutualistic; parasite/host;
…) and act as selection pressures on one
another
– “Evolutionary Arms Race”
Long legs
Good hearing
Sharp eyesight
Coevolution
Coevolution
Bird Bites
Eye Spot
Real Eye
What type of myth does this
illustrate?
What type of myth does this
illustrate?
• That need
creates the
genetic change
What type of myth does this
illustrate?
What type of myth does this
illustrate?
Good and bad gene
myth. (only
differential
reproductive
success).
Vicious cycle
• Pesticide resistance cycle
• Antibiotic resistance cycle