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Karyotypes
What is a Karyotype?
•
•
Karyotyping is a picture of an
individual’s chromosomes arranged in
homologous pairs.
They are stained with dye which
highlights A-T base pairs creating “G
Bands” (areas on the chromosome that
are rich in A-T pairs).
Karyotypes
• How would you
arrange the
chromosomes? On
what features would
you focus?
– Homologous pairs
(sets of chromatids
that carry the same
genetic material) are
identified by their
length, centromere
placement, and
banding pattern.
How can we use a Karyotype?
• Analysis of karyotypes requires a comparison
between a normal set of chromosomes and the
subject’s chromosomes.
• If there are missing chromosomes (monosomy),
or extra chromosomes (trisomy or polydactyl); or
if individual chromosomes have extensions or
deletions; the subject will then have a
chromosomal disorder.
Common Chromosomal
disorders:
• Klinefelter's Syndrome- one or more extra
sex chromosomes
– (i.e., XXY).
Common Chromosomal
disorders:
• Down's Syndrome– Trisomy 21 –
• extra chromosome 21.
Common Chromosomal
disorders:
• Trisomy 13 Syndrome- extra chromosome 13.
Genetic Disorders
Autosomal Dominant
• Each affected person usually has one
affected parent.
• There is a 50% chance that a child will
inherit the mutated gene.
• Only one mutated copy is needed, a
relatively small proportion of those who
inherit that mutation go on to develop the
disease.
Autosomal Dominant Diseases
• Huntingtons Disease –
Known for jerky
movements and dementia
• Marfan Syndrome –
Known to grow to above
average height. Some
have long slender limbs
with fingers and toes that
are also abnormally long
and slender.
Autosomal Recessive Disorder
• Two copies of the gene must be mutated
for a person to be affected by an
autosomal recessive disorder.
• An affected person usually has unaffected
parents who each carry a single copy of
the mutated gene (and are referred to as
carriers).
Autosomal Recessive Diseases
• Tay-Sach’s Syndrome –
Known for a “cherry-red" spot,
in the back of their eyes –
causes CNS to shut down and
become paralyzed – die at
young at 2-3yrs.
• Cystic Fibrosis - Cystic fibrosis
affects the exocrine (mucus)
glands of the lungs, liver,
pancreas, and intestines,
causing progressive disability
due to multisystem failure. –
die around teenage years
Sex-Linked (X Recessive)
• X-linked recessive disorders are also caused by
mutations in genes on the X chromosome.
• Males are more frequently affected than
females, and the chance of passing on the
disorder differs between men and women.
• The sons of a man with an X-linked recessive
disorder will not be affected, and his daughters
will carry one copy of the mutated gene.
Sex-Linked (X Recessive)
Diseases
• Fragile X Syndrome –
elongated face, large or
protruding ears, flat feet, larger
testicles in men, and low
muscle tone. Speech may
include cluttered or nervous
speech
• Muscular Dystrophy Progressive Muscular
Wasting, Poor Balance,
Walking Difficulty, Muscle
Contractures, Drooping
Eyelids, Scoliosis
Multi-Factorial Inheritance
• Diseases are likely associated with the
effects of multiple genes in combination
with lifestyle and environmental factors.
Multi-Factorial Diseases
• Autism - impaired social interaction
and communication, and restricted
and repetitive behavior
• Obesity - which excess body fat
has accumulated to such an extent
that health may be negatively
affected
• Multiple Sclerosis – autoimmune
condition in which the immune
system attacks the central nervous
system, leading to demyelination