DNA

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 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?

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

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?

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

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.