DNA
and Genes
What is the basis for all life?
Your personal code
Every cell in the body contains thousands of messages in code-the
genetic code. In a cell's nucleus you will find chromosomes,
which are strands of long molecules called deoxyribonucleic
acid (DNA). Sections of DNA, called genes, are coded messages
that influence everything from the color of your hair to stomach
enzymes. DNA and genes are found in all living things.
Your DNA is unique
Everyone's DNA is unique (except the DNA of identical twins).
This uniqueness reflects variation among individuals. One
way variation can occur is when DNA copies itself and there
is a change or misprint, called a mutation. Another way is
through sexual reproduction, which recombines genes. When
a male and female mate, each offspring inherits half its DNA
from its biological mother's egg and half from its biological
father's sperm. Thus, every child is genetically different
from its parents and siblings.
All life
shares DNA
How much DNA do you have in common with other living things?
about 50% with bananas
about 90% with mice
about 97.7% with gorillas
about 98.4% with chimpanzees
about 99.9% with the person next to you |
Evolution
How does evolution work?
What is evolution?
Evolution is the organizing concept
of the biological sciences, and it consists of two parts.
The first part is the fact that all known organisms are
descended from a common ancestor. The evidence is in the
fossil record and in each cell's DNA. The second part involves
the process of how evolution works.
Life evolves as DNA changes
Evolution occurs as the genetic traits of a population change
over time. Individuals that survive and reproduce pass their
genes to their offspring. Because some individuals happen
to be better adapted to their environment than other individuals,
they produce more offspring. As a result, their genes increase
in frequency in the group, or population. In this way, the
traits of the population change over time.
Some changes aid survival
Genes code for specific traits. Some traits are controlled
by a single gene; others by multiple genes. A trait may
be a physical characteristic such as hair color or shape
of teeth. It may also be a behavior, such as the instinct
to hide from a predator. If a trait helps an organism survive
in its environment, it is called an adaptation. Scientists
track evolution by studying changes in the adaptations of
a species, as well as changes in DNA.
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