Download Chromosomes Notes

CHROMOSOMES
DNA is a diffuse
spaghetti-like mass
called chromatin
during interphase.
Interphase is the
non-dividing phase.
DNA condenses into
chromosomes when the
cell is dividing.
Chromosomes are xshaped structures
containing two identical
copies of DNA
DNA wraps around histone proteins to maintain a
compact structure. (Each cell has about 3m of DNA)
Nonhistone proteins serve as scaffolding for DNA.
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CHROMOSOME STRUCTURE
Chromatids are
identical copies
of DNA.
The Centromere is
the structure that
holds two
chromatids together
until they divide.
HOMOLOGOUS CHROMOSOMES
Homologous
chromosomes are 2
chromosomes that have
the same genes.
However, they will be
different versions of the
gene (alleles)
You get one
chromosome of the pair
from each parent.
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AUTOSOMES & SEX CHROMOSOMES
Humans normally have 46
chromosomes (23 pairs from
each of our parents).
22 pairs are called autosomes.
One pair is sex chromosomes.
XX or XY
Haploid (1N) cells
(egg & sperm) have ½ as many
chromosomes.
Diploid (2N) cells (all others)
have 46 chromosomes.
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KARYOTYPES
A karyotype is a
picture of the
chromosomes in a
dividing cell.
They can be used
to identify genetic
diseases.
THE CELL CYCLE
A regular cycle
of growth and
division.
Interphase is
the longest
phase in the cell
cycle.
During
interphase the
cell grows and
prepares to
divide.
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CELL DIVISION
Mitosis: 1 parent and 2 daughter cells = 2N.
Meiosis: 1 parent and 4 daughter cells = 1N.
Photos from Modern Biology, Holt, Rinehart & Winston. 2002 unless otherwise noted.