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B1 - You and Your Genes

Differences between individuals of the same species are called variation. Variation may be due to
genetic factors or environmental factors.

Genetic Information

Genes carry the information needed for you to develop. Different genes control different
characteristics, e.g. the colour of your eyes.…

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A gene can have different versions, called alleles. For example, the gene for eye colour has two
alleles: brown and blue. For each gene, you inherit one allele from your father and one from your
mother. This is why you can have similarities to both of you parents.


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If the gene isn't present, i.e. if there are two X chromosomes present, the embryo will develop into a

If the gene is present, i.e. if there is an X chromosome and a Y chromosome, testes begin to develop.

After six weeks the testes start producing a hormone called…

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Genetic testing

It's possible to test a person for a faulty allele. If the tests are positive, couples must choose
whether to have children and risk passing on the disorder, to adopt a child instead, or to use embryo

Fetuses can also be tested. If the faulty allele is…

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The Implications of Genetic Testing

Before genetic testing can become a common practice, the following questions should be

How can mistakes be prevented? Is it right to interfere with nature? Who has the right to decide if a
disorder is worth living with?

There is always a difference between…

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Gene Therapy

Gene therapy is a potential treatment for certain genetic disorders. It involves inserting `healthy'
genes into cells in order to treat a disease.

The most common method uses genes from healthy people.

The genes are inserted into a modified virus, which infects the patient. The genes become a…

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Asexual Reproduction

Bacteria and other single-cell organisms can reproduce by dividing to form two `new' individuals. The
new individuals are clones (genetically identical to the parent).

This is asexual reproduction. Most plants and some animals can reproduce in this way.

Variation in organisms that reproduce asexually is normally only caused…


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