Transcript Gene Expression - Valhalla High School

Gene Expression
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Dr.Timmel
Vocabulary
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To truly understand how
our genes and
environment affect who
we are, we first need to
understand some content
specific vocabulary.
You should commit
these terms to memory!
Be like the elephant, and
never forget!
Genome: The complete genetic
material of an organism. It can be
either DNA or RNA.
In humans, our genome is
approximately 3,000,000,000 base
pairs long!
Human Genome Project
Gene: A segment of a
chromosome which codes for one
specific protein or trait.
Allele: The term used to describe
different versions of the same
gene. For example the blue eye
or brown eye allele.
Chromatin: Mass of genetic material
composed of DNA and proteins that
condense to form chromosomes in
eukaryotic cell division. Chromatin is
located in the cell's nucleus.
Chromatin consists of long, thin
strands that cannot be seen with a
compound light microscope.
Memory aid: Chromatin is thin.
Chromosome: Long, stringy
aggregates of genes that carry
heredity information and are
formed from condensed
chromatin.
These become visible under a
compound light microscope just
prior to cell division.
Chromatid: One of the two identical parts of
the chromosome. The two chromatids of a
single chromosome are called sister
chromatids.
Centromere: The centromere is the constricted
point at which the two chromatids forming the
chromosome are joined together.
What does a chromosome look like?
1 chromatid
Genotype: The genetic
constitution (the genome) of a
cell, an individual or an organism.
The genotype is all of the genes
within your cells.
Only identical twins (or tripets,
etc.) have the same genotype.
Phenotype: The observable
physical or biochemical
characteristics of an organism, as
determined by both genetic
makeup and environmental
influences.
Genotype + Environment =
Phenotype.
The snowshoe hare. The appearance of this animal
changes as the environmental conditions change.
The genotype is always the same.
Winter
Spring
Summer
Does the environment affect human
phenotypes?
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Absolutely! Light skinned people generally are paler
during the winter months. However, in the summer
when they are outside and exposed to more ultra violet
radiation, they tan.
Some diseases also result from a change in
environmental conditions. If your body is lacking in
vitamin C, you can get the disease called scurvy.
As a result, the shape of the long bones in your arms
and legs can become curved.
In conclusion
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Our outward appearance, or phenotype is
determined as much by our environment as it is
our genotype.
Our genotype never changes*, though our
phenotype does change over time.
*except in the case of a mutation.