Inside A Human Cell
Human chromosomes
stained with a special
chemical and viewed
under a high-powered
microscope
Chromosomes come in pairs
Cut out from picture and
match each in pairs
Karyotypes
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Before replication, the chromosomes
condense to form structures we can see
under a microscope.
A picture of a person’s chromosomes is
called a karyotype.
In a karyotype, homologous pairs are
matched and labeled.
How do we identify homologous
chromosome pairs?
1. Size
2. Stain with a dye to produce a pattern of
bands (banding pattern)
3. Position of the centromere
Centromere
Animated karyotyping
Gender determination
• Females have 2 “X” chromosomes.
• Males have 1 “X” and 1 “y” chromosome.
X
X
Female
X
y
Male
Why make karyotypes?
• Some diseases are caused by problems
with chromosomes
– Extra chromosomes
– Missing chromosomes
– Broken chromosomes
• Making karyotypes allows scientists to
identify these diseases.
Example karyotypes
Chromosomal Abnormalities
• Caused by problems in Meiosis
–
Errors in Meiosis
• Cannot be detected until the embryo
(baby) is already made
Detecting Chromosomal
Abnormalities
Amniocentesis
Chromosomal Abnormalities
• Some chromosomal abnormalities are
linked to maternal age (Down’s Syndrome)
Amniocentesis
• High-Risk mothers and mothers who have
odd test results may get an Amniocentesis
– An “amnio” is a sample of the amniotic fluid that surrounds the
baby. This fluid contains the baby’s cells.
Amniocentesis
• From the Amniocentesis, a karyotype can be
made.
Normal (complete set of chromosomes)
Disease (extra chromosome)