Download Science 9: Unit A – Biological Diversity

Science 9: Unit A –
Biological
Diversity
Topic 5: When Plans Change
DNA is the Genetic Code for
Life
• DNA = Deoxyribonucleic acid.
• DNA is a chemical found in the
nucleus of all cells.
• DNA forms long strands called
chromosomes. Every cell in a human
has 46 chromosomes in its nucleus.
• 23 chromosomes come from our
fathers, and 23 from our mothers.
The Structure of DNA
• DNA is in the form
of a coiled ladder.
• The ‘rungs’ of the
ladder are made
up of pairs of
chemicals called
nitrogen bases.
There are four
different nitrogen
bases.
The Four Nitrogen Bases
• The chemical rungs are four nitrogen
bases: Adenine (A), Thiamine (T),
Guanine (G), and Cytosine (C).
• The rungs of DNA are made up of
alternating pairs of these bases.
• Adenine can only pair up with
thiamine, and cytosine with guanine.
• The pattern of these repeating pairs
makes up our entire genetic code.
DNA, Proteins, and Genes
• DNA forms chromosomes. Different
sections of chromosomes act as blueprints
for different proteins to be made.
• A section of a chromosome that codes for
a single protein is called a GENE.
• A single chromosome can have hundreds
or thousands of genes, made up of billions
of base pairs.
• All cells and tissues are made up of
proteins.
The Discovery of DNA
• Canadian scientist, Oswald Avery
discovered DNA, but could not figure
out its structure or see it in a
microscope.
• Watson and Crick, an English and
American duo discovered DNA’s
structure. Their model explains how
just four nitrogen bases can account
for all of the biological diversity in
the world.
Layout of Chromosomes
• DNA is organized into chromosomes
in a cell’s nucleus.
• The chromosomes are organized into
pairs. So humans have 23 pairs of
chromosomes, one from each parent.
• Each chromosome in a pair has
genes that code for the same
protein, however, only the dominant
one is switched on.
What’s an allele?
• An allele is a form of a gene. For example,
the number of fingers on your hands is
based on a gene. There is more than one
allele for that gene. You can have 5
fingers (recessive allele) or 6 fingers
(dominant allele)
• Something like hair color can feature
many genes so that a child from brown
and blonde haired parents will have dirty
blonde hair.
• So for every gene you have, you have an
inactive allele.
Mitosis is Cell Reproduction
for Somatic Cells
• Is how somatic cells (non-gametes) reproduce in our
body. It works like binary fission.
• Step 1: The chromosomes in the parent cell nucleus
clone themselves.
• Step 2: The chromosomes all line up in the centre of
the nucleus.
• Step 3: The nucleus splits up and the cell stretches.
• Step 4: The chromosome twins split apart, going in
opposite directions.
• Step 5: The cell membrane pinches off, producing
two daughter clone cells, each with the same number
of chromosomes as the parent cell.
Meiosis is Cell Reproduction
to Form Gametes
• Is how gametes are formed.
Gametes must have half the # of
chromosomes of a regular cell since
they will be combining with each
other in sexual reproduction.
• This process is achieved by having a
regular cell divide twice. This
produces four gamete cells each with
only half the chromosomes of the
parent cell.
Meiosis and Mutations
• During meiosis, genes are swapped
between chromosomes so that the
chromosomes are now different. This
further increases variation in a
species.
• Your father’s chromosome may have
contained the allele for brown hair,
but during meiosis, this may have
been switched with the allele (from
Mom’s chromosome) for red hair.
Genetic Engineering
• Is the process of taking the genes of one
species and transplanting them into the
chromosomes of another organism. AKA
Gene splicing.
• Eg. Certain plants have been given the
gene for disease resistance from insect
species.
• These new species of GMOs (genetically
modified organisms or foods) are
extremely controversial as people do not
like the idea of scientists tampering with
nature.