Download DNA and Genes - Mr. Boettcher`s Class

DNA and Genes
Section 3.1 pp. 39 - 45
Learning Outcome
•I Can explain the differences, and roles
involved with chromosomes, genes, and
DNA
DNA is the Substance responsible for
inherited genetic variation
• Last class we learned about the Heritable Characteristics
• Heritable characteristics: characteristics that are transmitted from
generation to generation, such as eye color
• You have also learned that through the two different types of sexual
reproduction (asexual, and sexual) that offspring will either be identical to
their parent, or display traits from both parents and increase variation
• This variation is a result of the different Genes passed on by the parent
• A gene is a segment of DNA (deoxyribonucleic acid), responsible for a
specific trait of an organism
A• (1866)
Brief
History
into
DNA
Heritable Traits: a scientist monk named Gregory Mendel, noted that parents inherited parents’
traits, and that some traits were more common than others. These traits became known as dominant and
recessive traits. Mendel is known as the father of Genetics
• 6 Principles of Genetics derived
• 1) Traits are passed from one generation of a species to the next generation
• 2) Genes are the units of hereditary and determine traits of living things
• 3) Living things that reproduce sexually inherit genes in pairs, with one set
being contributed by both parents
• 4) Some genes are dominant, while others are recessive
• 5) Dominant genes tend to mask or hide traits of recessive genes when
offspring inherit a pair of genes where one is dominant and the other is
recessive
• 6) Genes may display incomplete dominance that is they may be neither
dominant nor recessive
DNA Debuts
• 1869: a 25 year old Swiss doctor
Friedrich Miescher was studying
lymph gland cells in Germany. He
was able to categorize the proteins
found present in the pus from the
bandages, but also found acidic
material inside the various cells
nuclei. In further study he
discovered that every cell
contained it and speculated that it
may carry hereditary information
• This material came to known as
deoxyribonucleic acid (DNA)
DNA a Transformer
• (1928) Fredrick Griffith
discovered that bacteria could
slot in genes from dead bacteria
(this led to genetic
transformation which underpins
most of the genetic engineering
done today)
• He took dead, disease
causing bacteria, and mixed
them with non-harmful
bacteria
• What he discovered was
that the non-harmful
bacteria, became harmful
DNA was in fact the Genetic Material
• (1944) Due to the complexity of genes, many
scientists had a hard time believing that DNA
could make up the genetic material in an
organism. Many believed the answers had to be
found in the different proteins (as their were
many different ones to choose from, and lots of
room for variation)
• Then Oswald Avery Set everyone straight
• He conducted experiments based off of Griffith’s, but
destroyed a different component each time
• Through a process of elimination he was able to
determine that DNA was indeed the carrier of genetic
material
• Although scientists were still skeptical till another team
of scientists were able to confirm his finding in 1952
The Shape of DNA
• (1953) James Watson and
Francis Crick were able to
produce the first model of
what the structure of DNA
would look like
• The Model resembled a
Spiraling Ladder
• They were awarded a Nobel
Prize for their discovery
Deceit
• Watson and Crick would not have discovered
the shape of DNA if had not been for the help
of a woman named Rosalind Franklin
• Rosalind Franklin was conducting her own
study on the shape of DNA using X-ray
Crystallography (taking x-ray images)
• Watson and Crick had been stumped until
viewing her Photo 51, which allowed them to
picture the shape as a spiraling ladder
• Sadly Franklin did not receive credit in the
discovery until after she had passed (1958) due
to high exposure of radiation
Chargaff’s Rules
• Developed two key rules in understanding the shape of
DNA
• First Rule
• Number of Guanine units equals the number of Cytosine
units, as well as the number of Adenine units equals the
number Thymine units
• These are the four bases that help make up DNA
• So A = T, and G = C
• This strongly hinted towards base pair make up
• Second Rule
• Composition of DNA varies from one species to another, in
particular the amount of A, G, T, and C.
• This help add strength to the argument that DNA had the
complexity needed to be responsible for genetic material
Gene Sequencing
• (1977) Fredrick Sanger
• Was a British Biochemist that
crafted a way to document
the nucleotide order known as
Sequencing
• Now scientists not only knew
the language, they could
actually put the words down
in the right order
Where are Genes Found
• Remember Grade 8 when we
referred to the Nucleus as the
“Command Center”
• We called it this because it
houses all of our DNA in each
and every cell, which means its
where all the genes are located
• Genes are made up of DNA, and
are responsible for determining
all of the specific traits of an
organism
Deoxyribonucleic Acid (DNA)
• This is the inherited material responsible for variation
• It was discovered in 1869
• It is made up of
• 2 Backbones made up of alternating phosphate and
sugar molecules, which are oriented on the outside
of the molecule
• Then Nitrogenous Bases (adenine, guanine,
cytosine, thymine), that face towards the inside
bonding with each other (through hydrogen bonds)
• The Shape
• Looks like a twisted ladder, forming a right handed
double helix
• The Nitrogenous Bases, form the rungs of the
ladder
Certain Bases only Pair with Certain Bases
• 2 Types of
Nitrogenous Bases (4
chemicals)
• Purines: Adenine, and
Guanine
• Pyrimidines: Thymine,
and Cytosine
• A Purine can only bond
with a Pyrimidines
• More specifically
• Adenine with Thymine
(2 hydrogen bonds)
• Guanine with Cytosine
(3 hydrogen bonds)
DNA contains Genes
• Gene: is a segment of DNA, located in one particular
place on a chromosome, which determines a specific
characteristic of an organism
• So a gene is a specific area on the DNA molecule that
represents the order of the Nitrogenous bases for that
specific region
• The arrangement of these “4 chemicals” (Nitrogenous
Bases) determines the genetic code
• Genetic Code: Arrangement of the 4 chemical “letters”
on a DNA molecule that can be arranged into words,
creating the instructions for an organism
The Chromosome
• A single DNA Molecule is arranged into a
package known as Chromosome
• Chromosome: A structure in which DNA
is arranged and in which Genes are
located
• The total DNA in one cell if spread out
would be about the length of 2- 3
meters (1 million times longer than the
cell it came from)
• To make it all fit DNA forms these
Chromosomes by wrapping the double
helix tightly around some proteins, until
a chromosome is formed
Number and Type of Chromosomes Vary
• So how many chromosomes are there?
• Well that depends on what type of
organisms
•
•
•
•
•
Humans have 46
Fruit Flies have 8
Rice Plants have 24
Dogs have 72
Most Bacteria have one or two circular
• Think of each chromosome as a
chapter in a book, in order to make a
complete Novel you require all of the
chapters
• Sex Chromosomes, Females are XX,
and Males are XY
Genes
• A single gene is an uninterrupted segment of DNA,
which contains the coded instructions for the
organism.
• Genes are located in the chromosomes
• Each chromosome has numerous gene locations
• Genes come in pairs
• Both genes in a pair carry DNA instructions for the
same thing
• Specific characteristic genes occupy matching
locations on the two chromosomes
• DNA code may not be exactly the same in both
locations
Alleles
• Is a possible form of a gene
• Remembering that genes are a specific
location in your DNA, and that you receive
half your DNA from your mother, and half
your DNA from your father, you have the
possibilities for two different copies of the
same gene (i.e. eye color, Blue from mom,
Brown from dad)
• This is where the idea dominant and
recessive genes comes into play
• Brown is Dominant, so it will show up over
blue if present