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DNA

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In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents.

What are chromosomes?

What makes this baby human? What determines her gender?

Chromosomes are located in the nuclei of cells.

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Chromosomes are made of a molecule called DNA.

DNA molecules carry the code that controls what cells are made of and what they do.

DNA stands for deoxyribonucleic

acid.

Each chromosome is a very long molecule

of tightly-coiled DNA.

Which part of a DNA molecule holds this information?

What is DNA?

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The structure of DNA

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How do you think the four bases are paired?

DNA base pairs

There are four types of bases, and they are usually identified by their initials.

A

T

C

G

adenine

cytosine

guanine

thymine

The double helix ‘ladder’ of a DNA molecule is held together by ‘rungs’ made from pairs of chemicals called bases.

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Base pairs hold the two strands of the DNA helix together.The rules for base pairing are…

There are millions of base pairs in a DNA molecule, and they always follow these rules.

‘A’ always pairs with ‘T’ ‘C’ always pairs with ‘G’

It is the sequence of these bases along a DNA molecule that forms the genetic code.

How do bases pair together?

A T C G

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Determining the structure of DNA

The structure of DNA was determined in 1953 by James Watson and Francis Crick.

Previous X-ray studies by Rosalind Franklin and Maurice Wilkins had suggested that DNA was a double helix.

Erwin Chargraff had found evidence that DNA bases occurred in pairs.

These discoveries were not fully accepted until other scientists had performed their own tests and experiments.

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Mapping the human genome

With the exception of identical twins, every human being has unique DNA. This means that individuals can be identified by a genetic ‘fingerprint’.

The Human Genome Project (HGP) was an international, publicly funded venture to sequence the three billion bases in the 20,000–25,000 genes of the human genome.

One of the subsidiary aims of the HGP was to address ethical and social concerns about how the information would be used. Can you think of any potential issues?

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Genetic jargon

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Glossary

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Multiple-choice quiz