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CHROMOSOMES
Structure & Composition
DNA in its raw form
White stringy
stuff = DNA
DNA can be seen under the
microscope in the form of
chromosomes
Prokaryotic DNA
Eukaryotic DNA
Chromosomes inside a cell can be
seen if stained
When
chromosomes are
“stringy” we call it
CHROMATIN
This is how DNA looks in an undividing cell
Zoom in to see the chromatin
DNA
Proteins (histones)
Chromatin = the DNA and proteins in the nucleus of an undividing cell
Once the chromatin super-coils and
condenses, they can look like this:
Chromatin
that is supercoiled
Chromatid – one
of two identical
parts of a
chromosome
This is how the DNA looks in a dividing cell – undergoing MITOSIS
Chromosome
Doubled
chromosome
Centromere holds
two sister
chromatids
together in a
chromosome that
has duplicated
itself.
Centromere – constricted area of a chromatid
Should this
segment of DNA
match the one
found on the
other chromatid?
Light vs. Electron Microscope
Picture of a Human’s Chromosomes
The Cell Cycle
• The cell cycle represents the events that take place as a cell grows, prepares
for division, and then divides into two new cells. Once two new cells have formed,
they each begin the cycle anew.
• Like other cycles, the cell cycle is broken into phases.
•Different types of cells and cells from different organisms may show slight
variations in some of the phases of the cycle, but the general course of events
is similar for all living things.
M = Mitosis (PMAT)
I = Interphase
G1 – growth
S – DNA synthesis
G2 – duplication of
organelles/compounds
G0 – resting/time out
Karyotype – a
photomicrograph
of the
chromosomes
found in a
dividing somatic
cell
Autosomes
First 22 pairs
Sex chromosomes
23rd pair - xx (female) or xy (male)
Homologous chromosomes “homologues”– two copies
(one maternal & one paternal) of each autosome
Diploid # for Humans = 46 (or 23 pairs)
Triple X Syndrome
47-XYY Jacob’s Syndrome
Despite having Trisomy 18,(Edward’s Syndrome) 5year-old Emily Blaise is going strong with the help of
her parents. The genetic condition causes severe
mental retardation, heart defects and takes the lives
of 90 percent of children before they reach 1 year.