Download Chromosomes

Chromosomes
(Eukaryotic DNA Structure)
• When the cell is
not dividing,
DNA is long and
stringy and
called chromatin.
• When the cell is
dividing, DNA is
tightly coiled around
proteins and is called
chromosomes.
Chromosome Numbers
• Each species has a • For example, humans
specific number of
have 46 chromosomes
chromosomes in the
in each body cell, dogs
nucleus in its cells.
have 78 in each body
cell.
Chromosome Numbers
• There is a tongue fern
that has 1262 in each
body cell!
• The number of
chromosomes that an
organism has is NOT
related to the
complexity of the
organism!
Chromosome Numbers
• In body cells, chromosomes come in pairs.
• Sex chromosomes are the pair of chromosomes
that determine the sex of the organism.
• In humans, the sex chromosomes are X and Y.
• Normal females have 2 X chromosomes, and
normal males have 1 X and 1 Y.
Chromosome Numbers
• All of the other
chromosomes are
called autosomes.
• So, in humans:
– 22 pairs or 44
chromosomes are
autosomes
– 1 pair or 2
chromosomes are sex
chromosomes
There are certain
disorders associated with
having too little or too
many chromosomes.
Chromosome Abnormalities
1.
Down syndrome – 3 copies of
chromosome #21 (trisomy 21)
Chromosomes Abnormalities
2. Turner syndrome – female with only 1X
chromosome (XO) (monosomy X)
Chromosome Abnormalities
3.
Klinefelter syndrome – male with XXY
Chromosome Abnormalities
4.
Patau syndrome – 3 copies of # 13
• Doctors can detect these conditions before
birth:
– Amniocentesis – removes amniotic fluid from
around baby …
– Chromosomes are photographed and
organized onto a chart called a karyotype.
• Chromosomes come in pairs because you
inherited one copy of the chromosome
from your mother and on copy of the
chromosome from your father.
• The two chromosomes in each pair are
called homologous chromosomes because
they have the same size and shape and
carry the same genes.
• Most cells in your body are diploid (2n),
which means they have 2 sets of
chromosomes (one from each parent).
The diploid number represents how many
chromosomes are in these cells.
• Sex cells (a.k.a. gametes, a.k.a. sperm
and egg) are haploid (n), which means
they only have 1 set of chromosomes.
The haploid number will always by half the
diploid number.
Organism
Human
# of chromosomes in
body cells (diploid
number)
46
Fruit fly
Dog
# of chromosomes in sex
cells (haploid number)
4
78
Sand dollar
26
Cat
16
Carrot
18
horse
64