Download Bio 1309 DNA as the The Ways of Change

Bio 1309
DNA as the The Ways of Change
Slide 1
DNA – What is it?
• DeoxyriboNucleic Acid,
• Large, complex
molecule in most living
cells (not in RBC)
• Double Helix
• Stores “Data” about you
• Involved in new cell and
organism reproduction
and protein creation
Slide 2
1
DNA - Structure
Always same width!
Slide 3
DNA – Reproduction vs Proteins
Slide 4
2
DNA & Cell Replication
• Cell makes a copy to
transmit information
from one generation
to the next
• DNA Replication
Slide 5
DNA & Cell Replication
• the cell divides and
each new cell get a
copy of the DNA
• new "daughter" cells
cells contain same
genetic info as the
parent cell
Slide 6
3
DNA Construction
• DNA – made of small
subunits called
nucleotides
• Four types of
nucleotides, each
contains a different
base= A, T, G, C
• A always pairs with T
• G always pairs with C
Bases:
A= Adenine
T= Thymine
G= Guanine
C= Cytosine
Slide 7
DNA – Nucleotide Bases
• DNA is made from the
same four nucleotides
for all organisms
Slide 8
4
DNA – Order Differences
• Nucleotides - like
beads on a string
• Differences in order
results in intra and
inter species
differences.
Slide 9
Slide 10
5
DNA - chromosome
•
•
DNA is organized as a chromosome w/ 2 strands
Each species - characteristic number of
chromosomes – 46 for example!
Slide 11
DNA & Genes
• chromosome
subdivided into
functional regions
called genes
• Each chromosome
has thousands of
genes
Slide 12
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DNA  Gene  Protein
• Each gene determines
the structure of one or
more proteins
• Each protein performs a
specific function in the
cell
Slide 13
DNA & Variations
• For any gene, there can
be variations
• Variations in a gene are
called alleles
• Example: freckles - an
allele that codes for
freckles and an allele
that codes for no
freckles
Slide 14
7
DNA& How It Works
in Eukaryotic Cells
• one allele from father
and another from
mother
• one or two alleles for
freckles = will have
freckles
• two alleles for no
freckles = no freckles
Slide 15
DNA is Universal
• Important facts about evolutionary history of life on
the earth:
– all living things have same basic DNA structure
– All organisms use DNA the same way
Slide 16
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Reproduction
• Parents pass a copy of
their DNA to each
offspring
• In asexual reproduction,
offspring from single
parent = offspring has
identical copy of DNA so
genetically identical to
their parents (remember
Bonnie Bassler?)
Slide 17
Asexual Reproduction
• genetic variation for
asexual reproduction,
only from mutation
• Offspring are copies, or
clones, of their parents
Slide 18
9
Sexual Reproduction
• Sexual reproduction =
new genetic
combinations so
offspring are genetically
different from their
parents
• Each provides ½ the
genetic information
Slide 19
Sexual Reproduction & Meiosis
• Sexual reproduction - more complex than asexual
• To prevent too many chromosomes in each new
generation, organisms make special reproductive
cells with 1/2 the regular chromosome number, yet
containing one full set of genes
• Called meiosis (a reduction division)
• Ploidy (haploid or diploid) refers to the chromosome number
state
Slide 20
10
Meiosisn
• Meiosis starts in diploid
cells in sex organs
– Ovaries in females
– Testes in males
• Diploid cells have two
full sets of
chromosomes
Slide 21
Meiosis = shuffling
•
•
Meiosis separates the chromosomes into two complete but separate sets
original chromosomes that came from each parent are shuffled and dealt
out randomly to the new cells being formed – known as recombination or
shuffling – for example:
Slide 22
11
Haploid Cells
• new cells with only one
set of chromosomes are
called haploid cells
– Eggs in females
– Sperm in males
Slide 23
Fertilization
• haploid egg fuses with
haploid sperms to
produce a new
individual called a
zygote
• zygote has two full sets
of chromosomes, it is
diploid
Slide 24
12
Sources of Genetic Variation
• Natural selection only
occurs if genetic
variation among the
individuals of a
population
Slide 25
Evolution and Genetic Variation
• Evolution happens
within a group of same
species individuals
• natural selection favors
traits that enable
individuals to best
survive and reproduce
in a given environment
– for example?
Thanks to Sheri Amsel
Slide 26
13
Where does Genetic Variation come from?
• Genetic variation stems
from two processes:
– Changes in the DNA
(mutations)
– Gene shuffling
(recombination) during
sexual reproduction
Slide 27
What is a Mutation?
• random and accidental,
permanent changes in
DNA
• Some are very small-only one unit of DNA
(one nucleotide) is
miscopied
Slide 28
14
Small Mutations-• change may seem
minor, but human
diseases such as cystic
fibrosis and sickle cell
anemia caused by this
kind of mutation
Slide 29
Larger Mutations
• larger errors in copying
that can involve large
parts of the DNA being
either lost, duplicated,
or put in the wrong
place where it does not
work correctly
Spontaneous – random change
Induced – chemical, radiation.
Point – change a single base
Nonsense – change a normal
codon into a stop codon
– Back-mutation – mutation is
reversed
– Frameshift – reading frame of
the mRNA changes
–
–
–
–
Slide 30
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Mutations- Explained
Slide 31
Environmental Sources of
Mutations
Direct Damage Caused by
Exposure of Cells to
Radiation or Harmful
Chemicals
• Exposure to ultraviolet
light from the sun,
radioactivity or certain
chemicals can change
the DNA molecules so
that they don't work
right
Slide 32
16
Recombination - heh
Slide 33
Recombination Possibilities
•
•
•
•
Humans = two sets of 23 chromosomes
> eight million different chromosome combinations each for eggs and
sperm
That means = at least 64 trillion possible combinations of egg and sperm,
or 64 trillion possible different genetic combinations for offspring from
two human individuals
64,000,000,000,000 ! (twelve zeros!)
Slide 34
17
Phenotypes?
• Alleles physical
manifestation, for
example - freckles or
not?
• Phenotypes were
envisioned by Darwin
when he used the term
trait
Slide 35
Genotype?
• actual alleles inherited from
parents
• For each gene, inherit one
allele from mother and one
from father
Slide 36
18
Example- Blood Typing
Slide 37
Studying Genetic Variation
Allele Frequencies
• An individual has two
alleles for a gene
– One from each parent
• Populations, on the
other hand, can have
many different alleles
for the same gene
Slide 38
19
Studying Genetic Variation
Allele Frequencies
• Let’s look at flower
color
• There are four possible
colors (alleles) of a
flower:
–
–
–
–
Red
White
Blue
Yellow
Slide 39
Studying Genetic Variation
Allele Frequencies
• In order to determine
how common an allele
is in a population,
scientists measure
allele frequency
– The word frequency
means the same as
proportion
Slide 40
20
Studying Genetic Variation
Allele Frequencies
• A percent is a type of
proportion - tells how
many out of 100
• Population geneticists =
scientists studying how
allele frequencies in
populations change
over time
Slide 41
Allele Frequency Oddities
•
•
•
Sometimes allele frequencies change in unexpected ways from one
generation to the next
In 1908, scientists developed a mathematical model to help explain how
allele frequencies can change over time - called the Hardy Weinberg
Equilibrium model
Hardy Weinberg Equilibrium model shows what happens in a sexuallyreproducing population that is not evolving
Slide 42
21
Hardy Weinberg Equilibrium model &
unchanging frequencies
• For allele frequencies staying the same from
generation to generation - set up a model of a
population that does not change to identify factors
that could cause changes in allele frequencies
• These factors are the underlying assumptions of the
model
• What are these assumptions?
Slide 43
Hardy Weinberg Equilibrium model assumptions
• Hardy Weinberg assumes:
– No mutations are occurring
– Large population size
– No movement of individuals and their alleles into or out of
the population
– Random mating, where each individual has an equal
chance of mating with another individual
– No natural selection
Slide 44
22
Hardy Weinberg Equilibrium model…
• model serves as
foundation for
understanding
evolution
• By varying these factors,
scientists can figure out
the various mechanisms
of evolution
Slide 45
Genetic Drift ?
• the change in the
frequency of an allele in a
population
• alleles in the offspring are
a sample of those in the
parents.
• chance plays a role in
determining whether a
given individual survives
and reproduces
Slide 46
23
Genetic Drift & allele frequency
• population allele frequency= fraction copies of one
gene that share a particular form
• genetic drift may cause alleles to disappear
completely from a population and reduces genetic
variation
Slide 47
Example:
Genetic Drift Simulation
Slide 48
24
Evolutionary Fitness
• In natural selection, the
environment acts on
populations to “select”
the individuals with the
traits (phenotypes) that
best help them to
survive and reproduce
• Limiting the gene pool?
Slide 49
Evolutionary Fitness
• Natural selection only
occurs when individuals
in a population differ in
reproductive success, or
evolutionary fitness
• Zimmer describes
evolutionary fitness as
“the rate at which a
genotype increases in a
population”
Slide 50
25
Evolutionary Fitness
• Focuses on genotypes
within a population –
not on individuals and
their offspring
Slide 51
Evolutionary Fitness & Offspring
• This means that when
comparing members of
the same population or
species to each other,
the ones with the most
offspring have the
highest evolutionary
fitness
Tribbles … thanks to Star Trek
Slide 52
26
Evolutionary Fitness – so what?
• an organism that is very physically "fit" may have a
very low evolutionary fitness if it does not reproduce
• It is true that individuals who are more physically fit
may have a higher chance of surviving in a difficult
environment, and that may also give them higher
evolutionary fitness.
• But not necessarily!!!
Slide 53
Studying Genetic Variation
Evolutionary Fitness
• Natural selection is not
survival of the strongest
• It is the survival and
reproduction of those
individuals best suited
to the existing
environment
Slide 54
27
Studying Genetic Variation
Evolutionary Fitness
• Even if the biggest and
strongest members of a
population survive, they
don't always reproduce
as well as smaller and
weaker members
Slide 55
Sexual Selection
• natural selection acts
on traits that contribute
to an organism's mating
success rather than
survival
• Example: Male cardinals
have bright red feathers
and females have duller
orange-brown feathers
Slide 56
28
Sexual Selection – brighter is better?
• Male bright color
attracts females, so the
brightest males have
more offspring
• This means= males with
bright red feathers have
higher evolutionary
fitness than males with
less colorful feathers
Slide 57
Sexual Selection - compromise
• Evolution is often a
compromise between
different kinds of
selection
• A trait that gives a
mating advantage to
the male increases his
evolutionary fitness
because he will mate
with more females
Slide 58
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Sexual Selection – might be dangerous!
• the same trait (red feathers?) might be a
serious liability when evading predators
•
A small reading that helps:
http://www.eebweb.arizona.edu/Animal_behavior/chase/chaseaway2a.htm
Slide 59
Sexual Selection – mating vs survival
• the fitness advantage of the trait (e.g. mating with
more females) must offset the survival disadvantage
of things like shortened lifespan
Yeah.
Yeah.
Whatever!
Slide 60
30
Studying Genetic Variation
Sexual Selection
http://www.pbs.org/wgbh/evolution/library/01/
6/quicktime/l_016_09_56.html
This link might not work…. Looking for a new
one.
Slide 61
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