Grade 9 Science
Unit 1 – Reproduction
What are you made of?
- A LEGO structure is made of many smaller blocks
Are all of the blocks the same? Why or why not?
- There are many different kinds of blocks because
they each serve a different purpose
- Our bodies are the same way
- Our bodies are made out of many, many, many
smaller blocks called Cells
- There are different kinds of cells in our body
because they each serve a different purpose
- You have skin cells, blood cells, brain cells, and many
other types of cells
- Each type of cell has a very specific job
- Your entire life depends on those cells doing their
jobs and working together
How does a Cell know what their job is?
- A cell acts like a factory
- some parts of the cell are in charge of creating
new materials
- some parts of the cell break down sugars to
provide energy for the cell
- In the middle of the cell, there is an organelle
called the Nucleus
- the Nucleus acts as the information centre of the cell
- it provides instructions to the cell so that it knows
what to build
- those instructions are written as long chains known as
DNA
Deoxyribonucleic Acid
- your cell reads these long chains and uses the
instructions to create chemicals (proteins) that are
necessary for them to do their job
Ex. Cells in the Pancreas create insulin, a chemical
that helps your body break down sugar
- without that DNA, your body wouldn’t be able to
create insulin which can cause medical problems
(diabetes)
- your DNA determines everything about you
- your physical traits (eye colour, hair colour, skin
colour, height, etc) depend entirely on your DNA
DNA
- DNA molecules are long chains of nucleotide bases
(pieces that fit together to create different patterns)
How many different pieces would you need to create the
variety we see in living things?
- there are more than 7,000,000,000 people on Earth and
(almost) every one of them has a unique set of DNA
- And that’s just humans. Other living things have
DNA, too.
- how many parts would DNA need to create so many
different living things, each of them with their own
unique set of DNA?
100?
1000?
1,000,000?
- there are four different nucleotide bases
A => Adenine
T => Thymine
C => Cytosine
G => Guanine
- your DNA is made up of only four different parts
- it is the order of the nucleotide bases that is
important
- a strand of DNA is a LONG chain of these bases
connected together in a specific order and the order
of your DNA is different than the order of everyone
else’s DNA
- much of your DNA would be exactly the same as
the person next to you
- this is why we all have skin and eyes, etc.
- BUT there are some differences and those
differences are what make each of us unique and
special
What does your DNA look like?
- DNA strands are a Double Helix shape
- each side is a chain of nucleotide bases
-the two chains connect together and wrap around
each other
- the nucleotide bases on one side match up
perfectly with a partner on the other side
A always matches up with T
C always matches up with G
- so, a strand of DNA is made up of two sides that
connect together
A–C–G–G–T–A–T–C–G
T–G–C–C–A–T–A–G–C
How is DNA stored in the Nucleus?
- DNA strands are very long
- in order to store them safely, DNA strands are
folded and coiled up into X-shaped structures called
Chromosomes
- the DNA is tightly packed into these Chromosomes and
only gets unfolded when your cell needs to read it
- humans have 46 Chromosomes arranged into 23 pairs
- the 23rd pair determines your gender
Girls have two X Chromosomes
Boys have an X and a Y Chromosome
- All living things have chromosomes, but they don’t all
have the same number
- this is why different species cannot mate
Genes
- your DNA is made up of very, very, very long strands of
information
- the instructions that your cell uses are broken up
into smaller segments of those strands
- think of it like a chapter of a book being divided up
into sentences
- your DNA is made up of many smaller
segments and each of those segments is a
specific instruction for your cell
- those segments are called Genes
- each chromosome contains different genes
- chromosomes in a pair will have the same genes,
but one from each parent
What does this have to do with Reproduction?
- you inherit your DNA from your parents
- each parent provides 23 chromosomes to the
offspring (child), one from each pair
- the 23 chromosomes from the father match up
with the 23 chromosomes from the mother meaning
the offspring has a full set of 46 chromosomes
- and, since your DNA determines everything about you,
you inherit all of your traits from your parents
- this is known as Heredity
But what if I don’t look like my Mom or Dad?
- you receive half a set of DNA from each parent
- your body has to use those two sets of DNA to
create a single body with one set of physical traits
- since some traits are Dominant over other traits,
some traits will be displayed while others are not
- this is called Expression
- each of your traits is based on how your body reads
your DNA and interprets how your chromosomes
will interact
- you may look like one parent, both parents, or
neither parent depending on how your traits are
expressed
Ex. Two brown eyed people can have a blue
eyed baby
- So, each cell in your body has a nucleus
- Each nucleus contains a full set of DNA
- you inherited that DNA from your parents
- that DNA determines your physical traits
What Makes Cells Different?
- each cell has a full set of DNA
- the skin cells at the tip of your toes have the same
DNA as the muscle cells in your eyebrows
- but how can they look completely different and have
completely different roles if they have the exact same set
of instructions?
- each cell starts out blank, without an assigned role
- these are called stem cells
- these stem cells are exposed to chemicals that tell
them which section of their DNA they are
responsible for reading
- since they only read a specific section of DNA,
they each read a different set of instructions
and perform a different function
- think of it like reading a play
- every actor gets the same script, but each one
only reads their own lines
Mutations (4.2)
- we have learned that the order of your DNA is
INCREDIBLY important
- the order of your DNA determines everything
about you
- but what happens if something messes up the
order of your DNA?
- every now and then, small mistakes happen when
your cells try to copy their DNA
- these mistakes can throw off the order of your
nucleotide bases
- these mistakes are called mutations
- mutations CAN lead to new traits
- occasionally, this reordered DNA will still code for a
trait, but it will be different from the original trait as
inherited from the parents
- there are three types of mutations
1) addition
- in addition mutations, an extra nucleotide base
is added to a DNA strand
Ex. A – C – T – C – G – T
A–C–G–T–C–G–T
- since DNA is read in sets of 3 (called a codon),
adding one nucleotide base throws off the
whole reading order
- imagine an English sentence:
The Cat Ate The Rat
- if we add one letter in the middle
Tgh eCa tAt eTh eRa t
- this can lead to completely unreadable DNA
2) deletion
- in a deletion mutation, one nucleotide base is
removed from a DNA strand
Ex. A – C – T – C – G – T
A–T–C–G–T
- just like in an addition mutation, this affects
the whole reading order
- imagine an English sentence:
The Cat Ate The Rat
- if we remove one letter from the middle
TeC atA teT heR at
3) Substitution
- in a substitution mutation, one nucleotide base
is switched with another at random
Ex. A – C – T – C – G – T
A–C–A–C–G–T
- imagine an English sentence:
The Cat Ate The Rat
- if we substitute one letter in the middle
The Bat Ate The Rat
- because this substitution only affects one set
of 3 and leaves the other sets unchanged, this
type of mutation leads to readable DNA, but the
instructions have been slightly changed
Affects of Mutations
- if mutations lead to a new trait, there are three possible
affects
1) positive
- some new traits can be incredibly helpful
Ex. Some people in our world are naturally
immune to AIDS
- these new traits are beneficial to survival
2) negative
- some new traits can be harmful
Ex. Cystic fibrosis is a very serious disease
that is caused by a mutation
- these new traits are detrimental to survival
3) neutral
- some mutations can be neither helpful nor
harmful
- it is possible that a slight change in DNA still
produces the same trait
Mutagens
- there are chemicals and other factors that can increase
your risk of mutations occurring
- some viruses can cause mutations
- cigarette smoke, radiation, pollution, and even
some household chemicals can cause mutations
- these factors are known as mutagens
Treatment for Mutations
- diseases caused by mutation can be very difficult to
cure
- because it is an error in your DNA itself, it can be
very hard to find a way to counteract the affects
- gene therapy is possible where doctors actually replace
the mutated DNA with corrected DNA, but this can be
incredibly risky for the patient
End of Section 1