Worlds of David Darling > Children's
Encyclopedia of Science > Genetics For Kids
IT'S IN YOUR GENES: DOES IDENTICAL DNA MAKE IDENTICAL PEOPLE?
Are Identical Twins Nature's Clones?
TWINS are offspring that result from
the same pregnancy. They can be either monozygotic or dizygotic.
Monozygotic twins are often referred to as identical twins.
They occur when a single sperm fertilizes a single egg. Later, this zygote
(a fertilized egg) divides to form two separate but genetically identical
embryos. Monozygotic twins are always of the same sex and share almost 100%
of their genes.
Dizygotic twins are formed when the mother releases two
distinct eggs and each is fertilized by a separate sperm. The twins can
be either the same or opposite sex. They share only up to 50% of their genes,
and so are as similar as any two siblings would be.
Conjoined twins are twins joined together by some region
of their bodies. There are different theories behind how conjoined twins
are formed, but the most accepted one suggests that conjoined twins are
monozygotic twins that do not fully separate during the splitting process.
| Point for discussion
Do twins have separate identities, even if their bodies are joined?
The Clone Zone
Unlike sexual reproduction, which combines the genetic material of two individuals,
cloning involves creating an identical copy of an organism or individual
by copying its genetic material. It's a bit like having your own identical
twin, but one who is much younger than you. There are two types of cloning:
|How Dolly the sheep was cloned
REPRODUCTIVE CLONING is when an individual is created who
is identical to someone else. The process starts with the nucleus of a cell
being extracted from the animal to be cloned. This nucleus contains all
of the animal's genetic information. It is then inserted into an enucleated
egg (a sex cell which has its own nucleus removed). An electrical current
is passed through the nucleus-egg combination to stimulate fusion and cell
division. Once this occurs, it is placed inside a host mother.
RESEARCH CLONING is designed to produce healthy cells that
are able to replace diseased or malfunctioning cells. This type of cloning
uses stem cells – cells that don't yet have a specific function, and
can be obtained from an embryo that is only a few days old.
The most famous case of cloning is Dolly the sheep. After being born in
1997, she became the most famous animal in the world. Cloning Dolly had
a low success rate per fertilized egg; she was born after 277 eggs were
used to create 29 embryos, which only produced three lambs at birth. Only
one of these survived.
Since Dolly's birth, dogs, cats, rabbits, cows, chickens, and pigs have
now also been cloned.
|Point for discussion
CLONES ARE JUST LIKE IDENTICAL TWINS, RIGHT?
Identical twins occur when after only one cell division, the cell
splits into two giving two identical embryos that then continue to
develop in the womb. They are natural clones, so what is the problem
with artificially generating genetically identical people?
"Savior Siblings" or "Spare Part Babies"? YOU decide"
A "savior sibling" is a brother or sister capable of donating lifesaving
tissue (such as blood, bone marrow, or stem cells) to an existing child
who is ill. A savior sibling has the same type of tissue and is genetically
very similar to his/her sibling.
How does it work?
A woman's eggs are fertilized with a man's sperm in a petri dish in the
lab. Embryos are produced. One or two cells are taken from an embryo when
it is two or three days old and genetic and tissue typing tests are run.
When an embryo is found that has the same type of tissue and similar genetics
as the sick sibling, it is implanted into the mother's womb. Once the baby
is born, stem cells are removed from the umbilical cord and stored for four
to six months when a transplant to the sick child can take place.
An example of why this process might be used
Thalassemia is a genetic condition that affects the red blood cells. People
with thalassemia have very vulnerable red blood cells that die easily. In
order to cope with this disease, regular blood transfusions are needed.
In this situation, the savior sibling is used to provide the blood required
Why might this be a problem?
Many people think that this process is wrong because it creates "designer
babies" who are only created to provide "spare parts" for their ill brother
or sister. Is this wrong? What do YOU think?
|Points for discussion
Is it right to create a child for a specific purpose? Why?
Is it ethical to deny a child the choice over how his or her body
Could that child then be called upon to provide further spare parts
against his or her will?
A finger print is an impression of the friction ridges from on the finger
tip. These friction ridges can also be found on the soles of the feet and
the palms of the hands. Friction ridges are formed during fetal development
at just 24 weeks. Throughout life, friction ridge patterns do not change.
Even when the skin tissue is injured the skin that grows back will have
the same pattern, unless the skin is damaged down to the dermis layer.
The purpose of these ridges is to give the fingers a firmer grasp and to
avoid slippage. These ridges therefore allow the fingers to grasp and pick
No two prints have ever been found to be exactly alike. Even those of identical
twins are different. Finger prints are not inherited. The basic pattern
(loop, whorl, or arch) may be the same in families but the minute details
Take your own prints and try to identify which general pattern you have.
Bringing the News to You
Science journalists understand and interpret very detailed, technical, and
sometimes jargon-laden information and make it into interesting reports
that are understandable to consumers of news media. They must also write
articles with a balance of fairness to both sides but also with a devotion
t o the facts.
You can find interesting and up-to-date science news stories by signing
up to the excellent science e-newsletter at http://www.life.org.uk/.
Read these articles critically, asking:
We also need to remember that all the information we receive through the
media has been through the editing process. For example, a journalist may
have an interesting story, but the amount that can be published will depend
on many factors, such as the amount of other news to be reported that day.
- What is the aim of the article? – To inform?
To entertain? To persuade? To advise?
- Who is the author of the article? – Are they
an expert, or not? Are they a supporter of the science they are writing
about, or not?
- What is the bias of the article? Is it in favor of,
or against the scientific research it is about? Is it possible to be
unbiased on ethical issues?
- What publication (which specific newspaper, magazine,
journal, or website) is it from? What influence will this have?
- What audience is it intended for> Has this affected
the amount or type of information involved?
Find a science article that is at least 10 paragraphs long. Now imagine
that you are the journalist that has written this story. Your editor tells
you that another more important story has to be reported too, and now you
can only used a maximum of 100 words in your article. Cut down the article
to the new word limit.
Consider: What are the essential facts of the story? What is the main message
that needs to be communicated?
Be the Journalist!
A commercial science company opened its door to the public yesterday, for
the first time in history offering to clone pets at a prince of $10,000.
Do you think that pets should be cloned? In 200 words, write a persuasive
short opinion on this topic.
Further Information for Teachers
How to Use the Ballot Sheets
This activity works best as a class group activity.
Hand out the savior sibling background sheet and discuss the different views
the students might have on this topic: is it right to make a baby for spare
Print and cut out the savior sibling ballot sheets and hand them out so
everyone has one each. Instruct the students to fill in the statements on
the card but not write their names on it.
When they have answered, fold the paper and pop it into a ballot box. Pull
the answers at random and use them as a means for stimulating discussion
about their opinions. You may wish to put their ideas on a flip chart.
Loops occur in about 60–70% of fingerprint patterns encountered. One
or more of the ridges enters on either side of the impression, re-curves,
and terminates on or in the direction of the side where the ridge or ridges
Whorls are seen in about 25–35% of fingerprint patterns encountered.
In a whorl, some of the ridges make a turn through at least one circuit.
Arches are found in about 5% pf the fingerprint patterns encountered. The
ridges run from one side of the pattern to the other, making no backward
To help students plan their own scientific article, you can try the graphic
organizer technique. Give them a sheet of paper to present their ideas in
the following way:
Green triangle: This represents the main idea of the article, e.g., "Scientist
clones humans. This is dangerous."
Yellow square: Four corners for four separate facts that support the main
idea of the article.
Red circle: Opinion of the author. (Red for "stop and think")
Also On This Site
If you found this page useful, you may also wish to check out the following
resource also on this web site:
Genetic Engineering: Redrawing
the Blueprint of Life
a complete on-line book by David Darling in the Beyond 2000 series.