Science 24 Tutorial – December 2nd.
Go over assignments due this week. Test on Friday!
Go over information on genetics at end of last tutorial (See below).
In U3L6, we begin our study of genetics.
What is genetics?
Ans. Genetics is the study of how characteristics or traits are passed from parents to
offspring.
The human body cells contain 46 chromosomes arranged in 23 pairs that hold all the
genetic information. One chromosome of each pair comes from the mother and the other
chromosome of each pair comes from the father. Human sex cells (egg or sperm) contain
half the number of chromosomes (23). Females have two X chromosomes in their cells,
while males have one x or one y chromosome. When an egg is fertilized with an Xcontaining sperm, the offspring is XX (girl), when an egg is fertilized by a y-containing
sperm, the offspring is XY, a male.
In lesson 6, you will be learning about Gregor Mendel’s work with pea plants and how he
learned about how traits can be passed on from one generation to the next.
Mendel determined that each organism contains two factors for each trait (eg. height,
colour, pod shape etc.)
Geneticists tend to use capital and lower-case letters to name the factors for any trait. The
actual letter can change, depending on what is being recorded, but the use of capital and
lower-case letters is consistent. These two letters represent the genotype or combination
of genes. Capital letters represent dominant genes. Lower case letter represent recessive
genes.
For any trait, an individual likely has one of the following pairs:
• DD — two dominant factors.
• dd — two recessive factors.
• Dd — one dominant gene and one recessive gene for a trait. This is called a hybrid.
Can somebody tell me what the difference is between the word “phenotype” and
“genotype”?
Genotype – genetics Eg. Tt
Phenotype – how it looks. Eg. tall.
Geneticists use something called a Punnett square to predict the probability of offspring
inheriting certain traits.
Turn to page 217 in your text. (Explain that the letter T represents the dominant gene for
tallness, which is the tall gene. The letter t represents the recessive gene for tallness.)
During reproduction, chromosomes separate so that each sperm or egg cell gets only one
chromosome of each kind. As a result, only one gene for each trait is passed on to the
offspring from each parent.) Go over the punnett squares in the text.
-Describe the appearance of each offspring in A, B, C, and D.
-Why were there no short plants in C, even though one plant was short?
(Slide #5) In the assignment for U3L8, the last question (#6) says:
“Complete a chart. In the first column, list the four possible combinations of genotypes
produced in the offspring when both parents have one dominant yellow gene and one
recessive green gene. In the second column write the corresponding phenotype of each
offspring.
How do we begin? (draw the punnett square)
Which colour in dominant? Ans. Yellow
Which colour is recessive? Ans. Green
Genotype
yy
Yy
Yy
YY
Phenotype
green
yellow
yellow
yellow
Let’s now look at the worksheet that you were supposed to try for U3L8 called “Drawing
Punnett Squares”. (Complete on slides)
Turn to page 220 and complete the Try this. Gene A produces normal haemoglobin,
Gene a produces defective haemoglobin which causes sickle-cell anemia.
In U3L9, you will learn about Pedigree. A pedigree is a diagram that shows the history
of a trait from generation to generation. Pedigrees are designed to show all expressions
of a trait, such as straight or cury hair.
Pedigrees are often used to help figure out someone's genotype. This can help if someone
may have inherited a specific disease. Analyzing the genotype of a couple can determine
the chances of the pair producing offspring with a specific disease.
A pedigree shows the physical expression, or phenotype, of a trait. It does not show the
genotype. For example, a pedigree may indicate that a man has dimples, which is a
dominant trait, but it does not show what combination of genes he has (Dd) or (DD) for
the trait.
Slide 9 – Interpreting a Pedigree (Students are to download these two documents
and complete them for U3L9). Complete with students.
Slide 10 – Determining the Genotypes – Complete with the students.
In U3L10, you will learn about genetic disorders and genetic research. You may
sometimes wonder why some people get diseases and others do not. Gene mutations can
result in diseases. They result when there are mistakes in the base pair sequences.
Inherited genetic disorders often result from a change in base-pair sequencing (mutation),
missing genes, or from inheriting specific defective recessive genes.
Exposure to environmental factors called mutagens can also cause mutations in the DNA
that develop throughout an individual’s life. Mutagens include radiation; chemicals in
cigarettes, alcohol, drugs etc.
Provide some examples of mutagens to students. These should include:
• radiation such as X rays — Discuss why people wear lead aprons when a dentist X-rays
their teeth. Explain that children in Japan who were exposed to radiation from an
atomic bomb in 1945 suffered from a high risk of leukemia (cancer of the blood),
especially during the first 10 years after exposure. The survivors continue to suffer from
higher risks for other kinds of cancer.
• ultraviolet radiation from the Sun — Tell students that the total amount of Sun they get
over their lifetime and overexposure resulting in sunburn can cause skin cancer. Even
though many people get skin cancer when they are older, the damage that caused the
cancer occurred when they were children. Point out that most people get 80 percent of
their lifetime exposure to the Sun by 18 years of age. Tell them that the sunburn they
get this week may take 20 years or more to become skin cancer. Stress how important it
is to use protection against ultraviolet light.
Tell students that skin cancer occurs more often on the left side of the face in
North America and more often on the right side of the face in Australia. Ask them why
they think this occurs. (Answer: Australians drive on the opposite side of the road from
North Americans. Australian drivers are exposed to the Sun on the right side of the face
and North American drivers are exposed on the left side of the face.)
• drugs and alcohol — Pregnant women who consume any alcohol or take drugs (legal or
illegal) are risking the health of their unborn baby.
• toxic chemicals such as PCBs and many pesticides — It is important to prevent
exposure to these chemicals.
Explain why human embryos are at risk from mutagens. The fetus is directly
connected to the mother’s bloodstream by the placenta. Chemicals that a pregnant
woman is exposed to circulate in her bloodstream. Whatever is in the mother’s system
flows into the system of the fetus, often in dangerous levels because the fetus is so
small. Chemical exposure is especially dangerous during the first trimester when the
organs are developing.
What is the human genome project?
Ans. Scientists have identified 30 000 genes in the human DNA and determined the
sequences of the 3 billion chemical base pairs that make up human DNA.
As you know, animals have already been cloned and the potential is now there that a
human be cloned. How do you feel about this? (Discuss)
Under what circumstances (if any), do you think it would be acceptable to clone a
human?
Read the Think About it section of “To Clone or Not to Clone?” on page 224. Discuss.
Position
Point Might Support
(a) Reason for Support
The scientist
should not be
cloned.
• It is unfair to expect that a
clone must continue the
work of the scientist without
considering the clone’s
wishes.
• Cloning violates the
rights of the individual.
• The clone may have a
different personality
and grow up in a
different environment,
so make different
lifestyle choices.
• Technology is not well
developed. Who is
responsible for mistakes
in clones?
• Genetic mutations
might be passed on to
future generations.
• The psychological and
social effects on the
family and society are
not known (e.g., would
parents love a clone the
same way?).
• Some people might
want to clone people to
create super-athletes,
excellent soldiers, or
super-scientists.
• It is difficult to learn
more about cloning if
cloning is not allowed.
• Cloning the scientist
helps science move
forward.
• Through cloning
technology, scientists
might learn how to
repair damaged cells by
growing new cells and
replacing them.
• Mistakes could happen in
the cloning process.
• The clone might be treated
as a second-class citizen.
• It sets a dangerous
precedent.
The scientist
should be
cloned.
• Scientists should use
available technology.
• Her knowledge is too
valuable to lose.
• A cure may be found for the
scientist’s disease and be
used to treat the clone.
(b) Reason for Not Supporting
• Clones would most likely have the same
interests and abilities.
• Science moves forward by learning from
mistakes.
• If the clone is destined to be a brilliant
scientist, she will enjoy respect.
• An ethics committee would ensure that
cloning is not abused.
• Scientists do not know enough about the
effects of cloning humans.
• There are other ways to pass on her
knowledge (e.g., interviews, written
reports).
• A cure may not be found in the clone’s
lifetime. It may be unfair to expect the
clone to live with the knowledge of a
future terminal illness.