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2016-12-10
DNA IS THE INHERITED MATERIAL
RESPONSIBLE FOR VARIATION.
SCIENCE 9 – UNI T A: SECTION 3.0
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Science 9 Unit A Section 3.0
3.1 DNA – TRANSMITTER OF
GENETIC CODE
TEXTBOOK PAGES 38 – 45
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GENETICS
• Genetics is the study of how characteristics of living
things are transmitted from one generation of a
species to succeeding generations.
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CANADIAN CONTRIBUTION TO DNA
• In 1944, Canadian
scientist, Oswald Avery,
confirmed that DNA is
the material of
inheritance.
• He proposed that a
large molecule found in
cells’ nuclei is responsible
for storing information
and passing it on.
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*DNA*
• DNA stands for deoxyribonucleic
acid, and it is the inherited genetic
material found mainly in the nuclei
of the cells of living things.
• All living things contain DNA in their cells.
The DNA contains instructions for an
organisms’ characteristic features (i.e.
nose shape or hair colour, etc.).
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DNA IS FOUND IN THE
NUCLEUS OF A CELL
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FRANCIS CRICK & JAMES WATSON
Francis Crick & James Watson
British molecular
biologist,
biophysicist, &
neuroscientist
(1916 – 2004)
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American
molecular
biologist,
geneticist, &
zoologist
(1928 –
)
• In 1953, James
Watson and Francis
Crick revealed that
the same chemical
building blocks carry
the instructions
needed for the
diversity in our living
world.
• Awarded the 1962
Nobel Peace Prize for
their discoveries of
the structure of DNA.
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THE STRUCTURE OF DNA
• The DNA molecule can be
compared to a ladder that has
been twisted into a continuous
spiral.
• The vertical uprights of the
twisted molecular ladder are
identical all along its length.
• The overall shape of DNA is
helical (like the coil binding on
a spiral notebook or agenda).
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THE STRUCTURE OF DNA (CONTINUED)
• The ‘rungs’ of DNA
vary in composition.
• Each individual rung
pairs up just two of
the following four
chemicals:
•
•
•
•
#3
guanine (G)
cytosine (C)
adenine (A)
thiamine (T)
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THE FOUR CHEMICAL BASES OF DNA:
GCAT
• This arrangement
forms a code that
cells can read.
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THE STRUCTURE OF DNA (CONTINUED)
• The arrangement of these four chemicals, G, C,
A, and T, forms a code that cells can read.
• The genetic code is based on arranging the four
chemical “letters” into “words,” or instructions,
that describe how to make any particular
organism.
• In other words, all the blueprints for all the
species on Earth are written in the same
language!
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*CHROMOSOMES*
• DNA contains all the instructions for an
organism’s characteristic features, such as
the shape of your nose or the colour of
your hair.
• If the DNA from a typical human body cell was
stretched out, it would be about two metres long!
• To fit such a large amount of DNA into their
cells, organisms arrange their DNA into
packages called chromosomes.
#4
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CHROMOSOMES (CONTINUED)
• Each human cell nucleus contains 46 chromosomes,
except for those in the gametes (i.e. sperm and egg
cells), which contain half (23 chromosomes).
• Think of one chromosome as a single book in a series, and
the entire set of chromosomes as the complete series. If you
were missing a single book, you would be missing
information.
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CHROMOSOME PAIRS
• For humans, a complete set has 46 chromosomes.
• In most familiar organisms, the chromosomes are
organized into pairs.
• So the body cells of a human contain 23 pairs of
chromosomes.
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23 PAIRS OF CHROMOSOMES
= A FULL SET OF 46 CHROMOSOMES
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EXAMPLES IN OTHER ORGANISMS
Dogs have 78 chromosomes,
which is 39 pairs.
Cats have 38 chromosomes,
which is 19 pairs.
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WHY SO IMPORTANT?
• All of our nuclei, except for those in the gametes,
MUST have a complete set of chromosomes.
• Each chromosome is important and provides crucial
instructions for your characteristics.
• For example, chromosome #1 of a dog reads “make round
eye pupil”, whereas chromosome #2 of a cat reads “make
slit-shaped eye pupil”.
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HUMAN GENOME PROJECT
• The $3 billion government-funded Human Genome
Project (HGP) was an international scientific
research project with the goal of determining the
sequence of chemical base pairs which make up
human DNA, and of identifying and mapping all of
the genes of the human genome from both a
physical and functional standpoint.
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HUMAN GENOME PROJECT
(CONTINUED)
• Planning for the project
started in 1984, got underway
in 1990, and was declared
complete in 2003.
• Over 20 universities and research
centers in the United States,
United Kingdom, Japan, France,
Germany, and China were
involved.
• One discovery from the
project? There are
approximately 20 500 genes
in human beings, the same
range as in mice.
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SO WHAT CAN GO WRONG?
• One of the reasons scientists felt it was valuable to
identify the human genome was to help us identify
and understand genetic diseases and possible
cures.
• For example, chromosome abnormalities are missing, extra,
or irregular portions of DNA.
• They usually occur when there is an error in cell division
following meiosis or mitosis.
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EXAMPLE: DOWN SYNDROME
• Down syndrome is a genetic disorder
caused when abnormal cell division
results in extra genetic material from
chromosome 21.
• It is typically associated with physical
growth delays, characteristic facial
features, and mild to moderate
intellectual disability.
• Occurs in about one per 1000 babies
born each year.
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EXAMPLE: TRISOMY 22
• Trisomy 22 is characterized by three
copies of chromosome 22 rather
than two.
• It is typically associated with growth
delays, unequal development of
the two sides of the body, distinctive
malformations of the head and
facial area, and intellectual
disability.
• It is a frequent cause of miscarriage
in the first trimester. Progression to
the second trimester and livebirth
are rare.
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EXAMPLE: ALS
• Amyotrophic lateral sclerosis, or ALS, or
Lou Gehrig’s Disease, is a nervous
system disease that causes muscle
weakness and impacts physical
function.
• Symptoms include stiff muscles, muscle
twitching, and gradually worsening
weakness due to muscle wasting.
• The cause is not known in 90 – 95% of
cases (associated with head trauma,
military service, drug use, contact
sports). About 5 – 10% of ALS cases are
inherited from a person’s parents. It is
associated with a defect on
chromosome 21 or mutations of
certain enzymes.
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*GENES*
• A gene is an uninterrupted segment of DNA, which
contains coded instructions.
• Genes are located on the chromosomes. Genes
come in pairs and are located on the same spot of
different chromosomes.
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THE RELATIONSHIP:
CHROMOSOMES, DNA, AND GENES
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*ALLELE*
• 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.
• An allele is a form of
a gene.
#6
• For example, there
are genes for hair
colour, texture, and
length.
• The different hair
alleles, which could
include:
• Red, blonde, brunette
• Straight, curly, wavy
• Short, long
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ALLELES: FORMS OF A GENE
IN A PLANT
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SUMMARY
• DNA is located in the nucleus of each cell.
• DNA is packaged into 46 chromosomes.
• If you unwind a chromosome and look at a small
section of it, you are looking at a gene.
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HOMEWORK!
• Textbook
• Check and Reflect
• Page 45
• # 1 – 4, 7, 9, 10
• Read Topic 3.2
• Page 46 – 47
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3.2 CELL DIVISION
TEXTBOOK PAGES 46 – 48
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CELL DIVISION AND REPRODUCTION
Asexual reproduction
• Associated with mitosis.
#7
Sexual reproduction
• Associated with
meiosis.
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CELL DIVISION AND ASEXUAL
REPRODUCTION
• Recall:
• Asexual reproduction involves only
one parent. All of the offspring are
genetically identical to the parent.
• In single-celled organisms, binary
fission enables the parent cell to
split its contents equally between
two new cells.
• This ‘asexual reproduction’ (only
one parent needed) occurs in
the cells of multi-cellular
organisms and is known as
mitosis.
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MITOSIS (1:29)
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*MITOSIS*
• In multicellular organisms, mitosis is the process that
produces two new identical daughter cells from
one parent cell with the same number of
chromosomes.
• Mitosis occurs in the body cells of multicellular
organisms and is responsible for the growth and
cellular repair of a multicellular organism.
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MITOSIS (CONTINUED)
• In mitosis, the parent cell first duplicates its DNA and
each chromosome is doubled.
• When the split takes place, each new cell receives
a complete exact copy of the DNA from the parent
cell.
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THE BASICS OF MITOSIS
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CELL DIVISION AND SEXUAL
REPRODUCTION
• Recall:
• Sexual reproduction usually involves two individual
organisms.
• The offspring that are produced from this union have
genetically different characteristics, half from one parent
and the other half from the other parent - making a unique
offspring.
• In multi-cellular organisms, sexual reproduction is
associated with a process called meiosis.
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MEIOSIS (01:48)
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*MEIOSIS*
• Meiosis is a type of cell division
that produces cells with only
half the DNA of a normal cell.
• Because each gamete has
only half the DNA of a normal
cell, when the male and
female gametes unite, the
zygote has a complete set of
DNA.
#9
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*MEIOSIS*
• In order for a
gamete to contain
only one copy of
the different
chromosomes, cells
must divide twice.
• This produces four
daughter sex cells
from just one parent
cell.
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MALE GAMETE + FEMALE GAMETE =
ZYGOTE
SPERM
½
+
EGG
½
=
ZYGOTE
1 whole
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THE BASICS OF
MEIOSIS
#9
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MEIOSIS: Two cell divisions, four daughter cells
MITOSIS: One cell division, two daughter cells
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EXPLORE ONLINE
http://www.learnalberta.ca/content/secsu/
html/biological_diversity/mitosis/index.html
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RECALL: SEXUAL REPRODUCTION
• During sexual reproduction, the specialized sex cells
(gametes) unite to form a zygote, which develops
into the new organism.
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GIVE IT A TRY
(TEXTBOOK, PAGE 48)
Number of
chromosomes
Number of
Number of
Number of
Number of
Organism
in a cell at
chromosomes chromosomes chromosomes
pairs of
the end of
in a body cell in a gamete
in a zygote chromosomes
mitosis
Cabbage
18
Black
bear
38
23
Human
Peanut
40
#10
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HOMEWORK!
• Textbook
• Check and Reflect
• Page 48
• #2–6
• Read Topic 3.3
• Page 50 – 54
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3.3 PATTERNS OF
INHERITANCE
TEXTBOOK PAGES 50 – 54
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BREEDERS
• Darwin talked to people who bred pigeons for
show, message carrying, or other purposes.
• He realized that breeding works much the same
way as natural selection, and that many of the
same methods that breeders use can also occur in
nature and can explain the way organisms change
in nature.
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*TRAITS*
• Animal breeders have been selecting animals with
the most desirable characteristics, or traits.
• Traits are characteristics of organisms.
• Scientists can now explain the inherited patterns
they discovered in terms of alleles.
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“PLAYING GOD” VS. SURVIVAL OF THE
FITTEST
• Sometimes, to prevent unwanted outcomes, only
animals or plants with the most desirable traits are
“allowed” to reproduce.
• This is the idea of “controlled breeding”.
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*PUREBRED* VS. *HYBRID*
Purebred Organisms
Hybrid Organisms
• A purebred organism
has ancestors all with
the same form of a
trait.
#12
• A hybrid organism is
produced by crossing
two individuals (usually
purebreds) who carry
different forms of a
trait.
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INHERITANCE IN
• Pure-bloods/Muggles: • “Pure-bloods” are purebred
witches and wizards, or
muggles; that is, both of
their parents are
wizards/witches or both
muggles!
• Half-bloods:
• “Half-bloods” are half
witch/wizard, and half
human; that is, one of their
parents was a human
(muggle).
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EXAMPLE: BREEDING PUREBREDS
• If a purebred female white cat is bred with a
purebred male black cat:
• The offspring would all be hybrids.
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*DOMINANT* VS. *RECESSIVE*
Dominant Trait
Recessive Trait
• Dominant traits are the
outward form observed
when two oppositeacting alleles are
inherited.
• Recessive traits are the
outward form observed
only when two sameacting, non-dominant
alleles are inherited.
• For example, black coat
colour (fur) dominant trait
in cats.
#13
• For example, white coat
colour (fur) is a recessive
trait in cats.
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EXAMPLE: BREEDING PUREBREDS
• If a purebred female white cat is bred with a
purebred male black cat:
• The offspring would all have black fur, because black is a
dominant trait.
• The offspring would all be hybrids.
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PUREBRED & HYBRIDS
+ DOMINANT & RECESSIVE = …
• Purebred Black + Purebred Black = Purebred Black
• Purebred Black + Purebred White = Hybrid Black
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QUESTION TO THINK ABOUT
• What will the offspring look like if two hybrid black
cats breed?
• Even though the parents both have black fur, remember
that they are hybrids, which means they are ‘carriers’ for
white fur, even though the white fur does not show.
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GENOTYPE VS. PHENOTYPE
Genotype
Phenotype
• An organism’s genotype
is the genetic makeup of
the organism.
• An organism’s phenotype
is its outward appearance
(i.e. a black cat).
• Hint: Genotype = genes
• It is usually written as two
letters, which represent a
pair of chromosomes.
• Hint: phenotype = physical traits
• Capital letters refer to
dominant traits.
• Lower-case letters refer to
recessive traits.
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GENOTYPE EXAMPLE: FUR COLOUR
• For example, let’s use the letter “b” to refer to coat
(fur) colour in a cat.
• B = black fur (dominant)
• b = white fur (recessive)
i.
Since black is a dominant fur coat colour in cats, a
purebred, black cat will have the following genotype:
#14
BB
ii.
A purebred, white cat will have the following genotype:
iii.
A hybrid black cat will have the following genotype:
bb
Bb
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PUNNETT SQUARES
#15
Parent 1
Parent 2
• Punnett squares are
named for an
English geneticist,
Reginald Punnett.
• A Punnett square is
a chart which
predicts all possible
gene combinations
in a cross of parents
(whose genes are
known).
Science 9 Unit A Section 3.0
B
B
b
b
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HOW DO WE USE PUNNETT SQUARES?
• B – black (dominant)
• b – white (recessive)
• All of the offspring
produced will be
black hybrid kittens.
#16
Parent 1
Parent 2
• If a purebred black
cat is bred with a
white cat, use a
Punnett Square to
determine the colour
of the offspring
(phenotypes).
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PUNNETT SQUARES EXAMPLE 1
• B – black (dominant)
• b – white (recessive)
#16
Parent 1
Parent 2
• If two black hybrid
cats are bred, use a
Punnett Square to
determine the
potential
phenotypes of the
offspring.
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PUNNETT SQUARES EXAMPLE 2
• B – black (dominant)
• b – white (recessive)
#17
Parent 1
Parent 2
• If a purebred black
cat is bred with a
hybrid black cat,
use a Punnett
Square to
determine the % of
offspring that would
have black coats,
and white coats.
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PUNNETT SQUARES EXAMPLE 3
• B – black (dominant)
• b – white (recessive)
#18
Parent 1
Parent 2
• If a white cat is bred
with a hybrid black
cat, use a Punnett
Square to determine
the % of offspring that
would have black
coats, and white
coats, and identify
the % of offspring that
are ‘purebred’ and
‘hybrid’.
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THERE’S SOMETHING ABOUT
RECESSIVE TRAITS…
• A recessive trait will
ONLY appear in the
offspring if TWO
recessive alleles are
inherited, one from
the mother, and
one from the father.
#19
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EXAMPLE: COLOUR BLINDNESS
• Colour blindness is the
inability to see or perceive
colour differences under
normal lighting conditions.
• Colour blindness is a
recessive trait and the
related gene is carried on
the X chromosome. Males
have a higher probability of
being colour blind.
• Females have two X
chromosomes.
• Males have one X and one Y
chromosome.
• This means that for a female
to be colour-blind, she
would have to inherit the
gene from both her mother
and her father.
• On the other hand, since Y
chromosomes can only be
passed on from the father, a
male would only need to
inherit the gene from his
mother in order to be colour
blind.
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INHERITING COLOUR BLINDNESS
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EXAMPLE: COLOUR BLINDNESS
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*INCOMPLETE DOMINANCE*
• When no specific trait is truly dominant or recessive,
this is known as incomplete dominance.
• Incomplete dominance is a pattern of inheritance
seen when two different alleles are present at the
same gene location, but neither is dominant.
• When the alleles are neither dominant, nor
recessive, an intermediate trait will occur
(combining the two traits).
#20
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*INCOMPLETE DOMINANCE*
• Example: Snapdragon flowers
• A purebred red flower is crossed with a
purebred white flower and the offspring
are neither red nor white, and instead, the
flowers are pink.
+
#20
=
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SOME EXCEPTIONAL CASES DO EXIST…
• If offspring are unlike either parent, more than one
gene location and more than one allele may be
responsible for specific traits.
• Example: human eye colour or red hair
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EXAMPLE:
FETAL ALCOHOL SYNDROME
• When a woman drinks
alcohol during
pregnancy, she risks
giving birth to a child who
will pay the price — in
mental and physical
deficiencies — for his or
her entire life.
• Characteristics include:
developmental delay,
behavioural problems,
learning difficulties, facial
abnormalities, epilepsy,
poor coordination, poor
socialization skills.
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POSSIBLE REASONS?
• The complex mixing of the possible combinations for
a particular trait may account for the variation of
traits an offspring has.
• Even though genes play a vital role in determining
development, environmental factors can also have
a bearing on how DNA is interpreted and
developed.
#21
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EXAMPLE:
THALIDOMIDE
• Thalidomide first appeared in Germany on October
1st, 1957.
• It was marketed towards pregnant women to help
combat morning sickness.
• It was quickly being prescribed to thousands of
women and spread to most corners of the globe.
Nobody had any idea of what was to follow.
• The tests on thalidomide were conducted on
rodents which metabolize the drug in a different
way than humans. Later tests on rabbits and
monkeys produced the same horrific side effects as
in humans.
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“THALIDOMIDE BABIES”
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THALIDOMIDE (CONTINUED)
• In the late 1950s and early 1960s, more than 10 000
children in 46 countries were born with deformities
as a consequence of thalidomide use. It is not
known exactly how many worldwide victims of the
drug there have been, although estimates range
from 10,000 to 20,000.
• Thalidomide became available in Canada in late
1959. Although thalidomide was withdrawn from the
West German and United Kingdom markets by
December 1961, it remained legally available in
Canada until March 2, 1962, a full three months
later than its ban in other countries.
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LEADING MEANINGFUL LIVES:
ALVIN LAW, MOTIVATIONAL SPEAKER &
THALIDOMIDE SURVIVOR (4:21)
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HOMEWORK!
• Textbook
• Check and Reflect
• Page 54
• # 1, 2, 4 – 6
• Section 3.0 Review
Handout
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