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DNA and Genetics – Ch 11 and 12
The Importance of DNA
DNA answers these questions:
How do organisms reproduce & grow?
How do organisms heal themselves?
Why do we see differences in
organisms of the same species?
Before DNA was discovered, scientists
were concerned with the cause of
variability
• Eye and hair color
• Attached and detached
ear lobes
• Hair line
Scientists concerned with variability
in organisms thought that some
chemical caused the variability.
Even though they did not know what
the chemical (ultimately DNA)
looked like they knew some of the
mechanisms by which it acted.
Scientists used
experimentation like
Mendel’s pea plant crossing
to figure out the
mechanisms.
They called the variations in
characteristics Traits (Phenotype)
and the variations in the genes that
create the different traits are called
Alleles (Genotype).
Scientists discovered that for most
organisms, genes were passed
through a sexual process.
Heredity
• Every sexual organism
(including people)
have two genes for
every characteristic
• One will gene comes
from a male (father)
and one comes from a
female (mother)
Phenotype is your physical traits
and it is determined by Genotype
which is your genetic make-up.
Scientists Discovered that…
• Traits might be dominate or recessive
• For instance the brown eye allele (B) is dominate
over the blue eye allele (b). So, a person with the
alleles (Bb) will have brown eyes.
Alleles and Genes
B
b
Possibilities
BB
Bb
bb
homozygous
heterozygous
homozygous
Punnett Squares for Eye Color
B – Brown Eyes Dominate
b – blue eyes
Mother - BB
Father - bb
Complications to Heredity and the Simple
Dominant and Recessive Scheme
• Codominance
• Incomplete Dominance
• Polygenic Traits
• Multiple Alleles
Codominance – Do Punnett
Incomplete Dominance – Do Punnett
Multiple Alleles
Polygenic Traits – Traits are controlled
by more than one gene
A Scientist named Griffith helped us find
the molecule responsible for the traits.
Griffith’s Experiment
• Mice infected with the S strain pneumonia bacteria die
from pneumonia infection but mice infected with the R
strain pneumonia bacteria do not develop pneumonia.
Griffith cont’
Griffith thought that the bacteria may be
releasing a chemical poison
that killed the mice.
So he heat treated the bacteria to kill them.
Then, he injected the heat killed bacteria and the
chemicals in their environment to determine
whether the mice were dying from a poison. If
it was a chemical poison and not live bacteria,
the chemicals in their environment injected with
the bacteria should have still killed mice.
Griffith cont’
So it is not a chemical poison that
kills the mice.
Griffith does another experiment
which is mixing heat treated (killed)
deadly strain with the harmless strain
Griffith cont’
Griffith was also able to isolate both
harmless and deadly strains of bacteria
from the blood of these dead mice.
Griffith concluded that the harmless
strain had been "transformed" into the
lethal strain by a
"transforming principle".
Today, we know that the "transforming principle"
Griffith observed was the DNA.
While the deadly bacteria had been killed by heat
treatment their DNA survived. We know now that the
deadly bacteria have a protective coating (like armor)
that protects them from the host’s immune system.
Because the harmless bacteria still had access to the
deadly bacteria’s DNA, the harmless bacteria had the
instructions to build their own new protective coating
which made them deadly.
The exact nature of the transforming
principle (DNA) was verified in the
experiments done by Avery, McLeod
and McCarty and by Hershey and
Chase.
DNA
DNA …..
• Must be able to be passed along to the
next generation.
• The information must be easily read to
be useful.
• DNA must be easily replicated so cells
can replicate.
DNA is contains the
blueprints for all the proteins
in our body that regulate
chemical reactions and
provide structure
Structure of DNA
• Deoxyribonucleic Acid
– Phosphate
– Deoxyribose (Sugar)
– Nitrogenous Bases
• Adenine
• Guanine
• Cytosine
• Thymine
Bases (A, C, G, T)
Groups of Three Bases Code for Amino Acids (e.g. ATT)
Groups of Codons make Genes which determine a Trait
Groups of Genes are called Chromosomes
All Chromosomes is an organisms DNA
Genes  Chromosomes  DNA
DNA Molecules….
• Need to be very long to hold all the necessary
information. 1 meter of DNA in Human Nucleus
with roughly 4.5 billion base pairs.
• Coil into structures we call chromosomes
– Chromosomes are DNA wrapped around a protein
called histones
DNA
Proteins  DNA  Genes  Chromosomes
Humans have 46 chromosomes total with
23 being unique
Prokaryotes have one chromosome in
cytoplasm
Eukaryotes have more in nucleus
How do we make new cells with all
the Genetic Material (DNA)?
Recap of Mitosis
How is the DNA Replicated?
DNA Replicates – First
the strands are separated
by breaking the weak Hbonds hold the strands
together
Then, chaining proceeds
w/ complementary bases
(A & T and G & C)
creating matching strands
Enzymes called DNA Polymerase
help by separating the strands,
joining bases onto the separated
strands and proof-reading the newly
formed strands
How do parents only pass one set of
genes along when they have two?
The answer is Meiosis and
Sexual Reproduction
Meiosis is the reproduction and
division of gene sets or
chromosomes for the production of
sex cell or gametes
Normal Cell with its
two genes for a
SINGLE characteristic
Stages of Meiosis
(preparing of
gametes sex
cells)
Duplication of
Genes
1st Split
These would
be either eggs
or sperm
2nd Split
Sexual Reproduction –
Returning of 2N from 1N
Single (1N)
Chromosome
in each
gamete
(sex cell)
Zygote (2N)
which has two
chromosomes (sets
of genes) for each
characteristic
ZYGOTE will
DIVIDE VIA
MITOSIS and
Grow
What is the End Game for
DNA?
PROTEINS
First a part of the DNA (a gene) is
opened up that contains the
information for a particular protein.
Then another SINGLE
strand of genetic
material is made of the
code for the protein with
Thymine replaced by
Uracil
Transcription
(copying of DNA & Creating RNA)
&
Translation
(Making Proteins from RNA)
RNA – Ribonucleic Acid
Characteristics of RNA
• RNA is a single stranded, contains no thymine,
uracil replaces it. RNA is able to move
throughout the cell. It occurs in three forms.
– mRNA – messenger RNA takes information from
DNA (in the nucleus) to the ribosomes
– tRNA – transfer RNA bring amino acids to the
ribosomes for protein assembly
– rRNA-ribosomal RNA
Page 304 and 305 are great
for observing the function of all
types of RNA
Why make a copy of the
DNA?
Why make RNA?
Protein Synthesis
• The process of protein synthesis requires that
DNA be converted to mRNA (transcription) and
the information moved to the ribosomes on the
rough Endoplasmic Reticulum for assembly
(translation).
The DNA code
• The code functions in units of 3. There are
a minimum of 20 amino acids that need to
be coded for with only 4 letters that can be
used in the code. Therefore, the code has
be made of 3 letter “words”.
– DNA-triplets
– Also in groups of three
• mRNA-codons
• tRNA-anticodons
Other Terms You Should Know
• Introns – areas that do not code for proteins
• Exons – areas of DNA that code for protein
• Heterochromatin – areas of the chromosomes that
are heavily coiled and are no longer being used.
It is thought that these regions are not undergoing
transcription and are resting.
• Euchromatin – areas of chromosomes that are
used frequently.
The nucleus
Natural and Healthy Variation
Chromosomes not
Alleles and Cross-Over
MUTATIONS
Kinds of Mutations
• Gene Mutations
– Point mutations
• Wrong Base
– Insertions or Deletions are called Frameshift
Mutations
• DNA is read in groups of three which is a
CODON each of which spells out an amino acid.
If you insert or delete one base then all the
groups of three (amino acid) will be changed.
Chromosomal Mutations
• Remember, DNA is
sticky. During the
process of meiosis,
it gets snarled up
and breaks apart.
This causes new
combinations of
DNA to occur.
Oncogene
• An oncogene is a gene that is thought to cause
cancer. Some oncogenes are linked to viruses
(human papilloma virus), some are known to be
inherited, some are thought to be caused by
environmental factors. (Vaccination)
– Mutagen – factor in the environment that causes
DNA to change
– Carcinogen – an agent that tends to cause cancer
END