Biology (Holt)

The Human Genome Project

In February of 2001, scientists working on the Human Genome
Project published a working draft of the human genome sequence.
The sequence of an organism’s genome is the identification of all base
pairs that compose the DNA of the organism. The
is a research project that has linked over 20 scientific labo-
ratories in six countries. Teams of scientists, such as those shown
in Figure 6,cooperated to identify all 3.2 billionbase pairs of the
DNA that makes up the human genome. Scientists were surprised
by some of the discoveries they made.

The Geography of the Genome

One of the most surprising things about the human genome is the
large amount of DNA that does notencode proteins. In fact, only
1 to 1.5 percent of the human genome is DNA that codes for proteins.
Each human cell contains about six feet of DNA, but less than 1 inch
of that is devoted to exons. Recall that exons are sequences of
nucleotides that are transcribed and then translated. Exons are scat-
tered about the human genome in clumps that are not spread evenly
among chromosomes. For example, chromosome number 19 is
small and is packed with transcribed genes. The much larger chro-
mosomes 4 and 8, by contrast, have few transcribed genes. On most
human chromosomes, great stretches of untranscribed DNA fill the
chromosomes between scattered clusters of transcribed genes.

The Number of Human Genes

When they examine the complete sequence of the
human genome, scientists were surprised at how few
genes there actually are. Human cells contain only
about 30,000 to 40,000 genes. This is only about dou-
ble the number of genes in a fruit fly. And it is only
one-fourth of the 120,000 genes that scientists had
expected to find. How had scientists made this pre-
diction of the number of human genes, and why was
it wrong? When scientists had counted unique human
messenger RNA (mRNA) molecules, they had found
over 120,000. Each of these different forms of mRNA
molecule can, in turn, be translated into a unique pro-
tein. So the scientists expected to find as many genes
as there are types of mRNA molecules.

Project

Human Genome

Human Applications

of Genetic Engineering

SECTION 2 Human Applications of Genetic Engineering 233

Section 2

Objectives

Summarizetwo major

goals of the Human

Genome Project.

Describehow drugs

produced by genetic

engineering are

being used.

Summarizethe steps

involved in making a

genetically engineered

vaccine.

Describehow gene therapy

is being used to try to cure

genetic disorders.

Identifytwo different uses

for DNA fingerprints.

Key Terms

Human Genome

Project

vaccine

DNA fingerprint

Figure 6 Genetic Research.

Hundreds of scientists around the

world worked to identify the human

genome sequence.

3F

6A 6D

6A 6D

6A 6D

3C 6A 8B