What is a Karyotype?
Karyotype: picture of an individual’s
chromosomes arranged in homologous pairs.
Chromosomes are usually extracted during
METAPHASE of a cell. Why?
You can form a karyotype from any cell that is
going through metaphase.
You can identify the gender of the person by
looking at the sex chromosomes on the
karyotype.
XX Female
XY Male
Doctors can also run tests on fetuses to check
for chromosomal errors.
This test is called an amniocentesis.
What happens
when things go
wrong with the
chromosomes?
Nondisjunction
When homologous chromosomes or sister
chromatids fail to separate during meiosis.
-Can occur in anaphase I or II;
Resulting in gametes with
abnormal # of chromosomes.
It is not fully understood why nondisjunction
occurs. *usually occurs in women over 40
Nondisjunction
• Example of nondisjunction:
Trisomy-21 an error most likely during
meiosis I, causing 3 of the 21st
chromosome.
Commonly known as: Down’s Syndrome
Symptoms: characteristic facial features,
below average height, heart defects,
impaired immune system, varying degrees
of mental disability.
Other forms of Nondisjunction
Trisomy-13: (Patau Syndrome)
Due to an extra chromosome on
The 13th chromosome.
1 in 10,000 of children born.
There are varying degrees.
Symptoms: cleft lip, clenched
fist, close set eyes, mental
Retardation, etc.
More than 80% die in the first year.
Klinefelter’s Syndrome: (XXY Male)
When a male has an extra X chromosome in
most of their cells.
Most common symptom is infertility.
Most do not know they have it until puberty.
Have less testosterone, so lack some male
features.
**caused by nondisjunction
Turner Syndrome: (Monosomy-X)
Found in females that do not have the normal
XX in their cells. They only have one.
1 in 2000 live births.
Symptoms: swollen hands and feet, lack
female features after puberty, wide, webbed
neck, flat/broad chest, drooping eyes,
infertility.
Damaged Chromosomes
Chromosomes can also be damaged and
cause problems.
There are 4 types of changes that can occur
to chromosomes and cause varying
problems to the body.
Duplication: when part of the chromosome is
repeated. Not always fatal but can cause some
developmental abnormalities.
Deletion: when part of the chromosome is lost.
Inversion: reversing a section of the original
chromosome. (not as harmful)
Translocation: when a section of one
chromosome attaches to a NONhomologous
chromosome.
Jumping GENES
Transposons: where a section/gene of a
chromosome “jumps” to another
chromosome. Disrupting the genes.
Barbara McClintock discovered these in the
1940s with variations of corn. She
received the Nobel Prize in 1983 for her
pioneering work!