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DNA IS THE INHERITED
MATERIAL RESPONSIBLE FOR
VARIATION
KEY CONCEPTS

Chromosomes, genes, and DNA

Cell Division

Inheritance
LEARNING OUTCOMES
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Describe relationship among chromosomes, genes and
DNA, and their role in storing genetic information.
Distinguish between cell division during asexual
reproduction and cell division during sexual
reproduction.
Investigate the transmission of characteristics from
parents to offspring, and identify patterns of
inheritance.
Identify examples of dominant and recessive
characteristics.
DNA IS LANGUAGE

Double helix in each of your 100 trillion cells… If
you unraveled it, it would be 6 feet long in each of
your cells (or about 2 metres)- 1,000,000 times
longer than the cell it came from!
MADE UP OF A 4 CHARACTER CHEMICAL
ALPHABET…



That spells out instructions for all proteins of
which your body is constructed.
Most efficient storage system we know of in
the universe.
Mapping Human Genome- “Today we are
learning the language in which God created life.”
HUMAN GENE MAP COMPLETED IN
FEBRUARY 2001
Or
at least a “first draft”!
Estimated
that humans have
about 30,000 genes.
Previously
scientists thought
we had about 100,000 genes.
CONSIDER THE BENGAL TIGER

One of the most endangered species on Earth
1900- 40,000... TODAY 4,500 -6,000
 Most
scientists believe it will disappear
unless humans act to prevent its
extinction (interesting as humans greatly
contributed to possible extinction).
A
captive breeding program is one
important way to save the Bengal tigers
(and other species threatened with
extinction). Ex Situ
VARIATION?



Like all sexually reproducing species, their best
chance of survival is if there is a lot of variation
within the species.
Without variation, the species would be
unable to survive changes in the
environment.
With so few Bengal tigers left, how can variation
be maintained?
THROUGH MAPPING THEIR GENOME



Using modern technology, geneticists and zoo
staff can analyze the tigers’ genetic material to
determine how similar two tigers are.
They can even predict the characteristics the
cubs are likely to have.
Artificial Selection: Scientists will select
which characteristics will be passed on through a
captive breading program.
DNA- TRANSMITTER OF GENETIC CODE
REMEMBER…
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The offspring of a sexually reproducing
species are not genetically identical to their
parents.
However, these offspring do resemble their
parents because particular characteristics are
passed on from generation to generation.
People have used this understanding to produce
many different breeds of domestic plants and
animals.
DOGS


The goal of breeding purebred dogs was not
variety, but specific, desired characteristics.
The result, however, has made Canis familiaris
one of the most physically varied species on
Earth.
DNA

Why do the puppies of Chihuahua dogs turn out to
be Chihuahuas? Why don’t they turn out to look
like Dalmations instead?
THE REASON:
 Is
that the Chihuahua parents pass on a
“blue print” to their offspring, so that
each puppy receives a complete set of
instructions for making a Chihuahua dog.
 Every
multicellular organism on
Earth contains a blueprint for
making a copy of itself in each of its
body cells.
IMAGINE THE AMOUNT OF INFORMATION
THAT MUST BE IN THESE BLUEPRINTS
 And
how many different blueprints
there are… one for every kind of life
on earth.
 What
could store so much
information and pass it along from
generation to generation?
CANADIAN SCIENTIST OSWALD AVERY

Helped to answer this question when he proposed
that a large molecule first found in cells’ nuclei is
responsible for storing such information and
passing it on.
DEOXYRIBONUCLEIC ACID
Or
DNA for short, is the
inherited material responsible
for variation.
All
living organisms contain
DNA in their cells.
If
the organism has a nucleus,
DNA is found in the nucleus.
DNA AND THE GENETIC CODE



DNA was first discovered in 1869, but scientists
didn’t really know much about it.
After analyzing cells of may different organisms,
from bacteria to plants and animals, scientists
found DNA in all of them.
In 1944 Avery confirmed that DNA was the
material of inheritance.
WATSON AND CRICK



Solved a puzzle which was one of the greatest
scientific achievements of the last century.
They revealed how the same chemical
building blocks could carry such a wide range
of instructions needed for the diversity we
observe in the living world.
The DNA molecule can be compared to a ladder
that has been twisted into a continuous spiral.
G, C, A & T
 The
uprights of the twisted molecular
ladder are all identical.
 The
“rungs” vary in composition, and are
made up of pairs of 4 different chemicals.
 Guanine
& Cytosine
 Adenine & Thiamine
G ALWAYS pairs with C
 A ALWAYS pairs with T


Therefore, DNA is really made up of 2 strands;
one strand has its own base sequence, and the
other strand has a complementary base
sequence. For example:
ATGCGTAATGC
 TACGCATTACG

...one strand
...complementary strand
THE ARRANGEMENT OF THESE 4
CHEMICALS
 G,
C, A & T, forms a code that cells can
read.
 Like
the way the 26 letters of our
alphabet can be arranged into millions of
words.
 The
genetic code is based on arranging
the 4 chemical letters into “words” or
“instructions” that describe how to make
any particular organism.
BROWN EYES & BLUE EYES
Brown eyes sequence: AAAAGCGCCCGGG
 Blue eyes sequence:
AAATGCGCCCGCG



The letters that are in red are the only
bases that are different between the two
sequences.
Genes in general are about 1000 bases
long. Therefore, you will see variation in the
sequences from individual to individual. The
general rule is that individuals that are the same
species will have DNA sequences that are very
similar.
CHROMOSOMES
CHROMOSOMES
 DNA
contains all the instructions for an
organism’s characteristic features.
 Because
each organism has so many
physical and chemical characteristics,
there is a lot of DNA in each cell.
 To
fit so much DNA into their cells,
organisms arranger their DNA into
packages called chromosomes.
IN PLANTS & ANIMALS
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Chromosomes are located inside the cell nucleus.
Each human cell nucleus contains 46
chromosomes.
Think of a chromosome as a single book in a set
of encyclopedias. If you are missing one or more
books, you are missing some important
information.
One chromosome contains only part of the
instructions for making a human.
All
of human nuclei, except for
those in the gametes (sperm &
egg have 23 chromosomes… you
get half the genetic info you need
from each parent) must have a
complete set of chromosomes.
What
happens if they don’t?
CHROMOSOME ABNORMALITIES
 Genetic
disorders are caused by
differences in a person’s genetic material.
 Sometimes
the difference is large and
involves entire chromosomes. For
example, a person might be born with an
extra or missing chromosome, or there
might be a large section of a chromosome
added, missing, or moved to a different
location in the genome.
MANY TIMES
 An
embryo with an extra or missing
chromosome will not be viable with life
and will miscarry, often early in
pregnancy before a woman would even
know she is pregnant.
 However,
there are some chromosomes
that can be missing or extra and be viable
with life.
DOWN SYNDROME (EXTRA CHROMOSOME
21
EDWARD SYNDROME (EXTRA
CHROMOSOME 18)
TURNER SYNDROME (MISSING X
CHROMOSOME)
Because
each chromosome
holds a different set of genes,
the effects of extra/missing
chromosomes vary depending on
which chromosome is involved.
BUBBLE BOY (SEVERE COMBINED IMMUNE
DEFICIENCY)
LOCATED ON X CHROMOSOME
Newborns
in Ontario are now
among the first in Canada to
be screened for Severe
Combined Immune
Deficiency Syndrome, a
genetic disorder often
nicknamed “bubble boy
disease.” (as of 2013).
CHILDREN WITH SCID


Have gene mutations that render their immune
systems almost useless and make it difficult for
them to fight any form of infection.
If left undetected, the illness typically leads to
death early in life. SCID was nicknamed “bubble
boy disease” after a Texas boy named David
Vetter was born in 1971 with the condition. He
was placed in a plastic bubble within minutes of
his birth and lived his whole life in a sterile
environment. He died at the age of 12 after a
failed bone marrow transplant led to lymphoma.
CHROMOSOME NUMBERS VARY FROM
SPECIES TO SPECIES.

A complete set in humans: 46 or 23 pairs

A complete set in dogs: 78 or 39 pairs

A complete set in cats: 38 or 19 pairs

The composition varies as well. A dog’s
chromosomes must contain genetic code that
reads “make a tail”. Such differences are the
source of diversity from one species to another.
GENES
GENES (MOST EARLY RESEARCH WAS
CONDUCTED ON A FRUIT FLY)
 Scientists
currently believe that
genes are responsible for the
inheritance of an organism’s
characteristic features.
A
single gene is an uninterrupted
segment of DNA, which contains
coded information.
 Genes
are located on the
chromosomes.
 Each
chromosome contains
numerous gene locations.
LIKE CHROMOSOMES
 Genes
come in pairs.
 Both
genes in a pair carry DNA
instructions for the same thing.
(like leg-length in a fruit fly)
 In
a fruit fly, the two leg-length
genes occupy matching locations on
the two chromosomes, but the DNA
code may not be exactly the same in
both locations.
CHROMOSOMES & GENE PAIRS
OFFSPRING INHERIT GENES FROM BOTH
PARENTS

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A fruit fly, for example, inherits one gene for leg
length from its mother, and one from its father.
The leg-length gene exists in 2 possible forms,
long leg or short leg.
The wing shape gene also exists in two
possible forms, long or dumpy.
So the two genes in a particular pair may not be
identical (if the fly inherited a short leg gene and
a long leg gene for example).
ALLELES
ALLELES
 Most
genes in most species exist in
an array of possible forms that differ
as to their exact DNA sequence.
 These
possible forms are known as
alleles.
CHROMOSOMES, GENES, AND ALLELES ARE
LINKED TO INHERITED CHARACTERISTICS.

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Think of a dog... All dogs belong to the same
species, and all ordinary, healthy dogs have a
hairy coat.
We could begin by thinking that a “hairy coat” is
an example of an inherited characteristic.
But when we look at dogs, we see many
versions of a “hairy coat”. Hair may be
straight or curly, long or short, course or fine,
and may come in many, many colour
combinations.
OBSERVING THIS VARIATION WE CAN MAKE
3 INFERENCES
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1. We can be pretty sure that “Hairy Coat” is
more than just a single characteristic. It
must involve a combination of several
characteristics.
2. More than one gene pair might be
involved in determining a dog’s coat. For
example, there could be one gene pair for hair
length, one for wavy, etc.
3. There may be several possible alleles for
each gene pair.
CHECK AND REFLECT
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