11/13/2015
Barr Bodies
and Blood Types
Barr Bodies
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11/13/2015
X-inactivation in female mammals

In females, one of the two X chromosomes
in each somatic (body) cell becomes
inactive during embryonic development

Why?
◦ Cells of females and males would have same
effective dose of genes on the X chromosome

Inactive X chromosomes called Barr bodies
BARR BODY

Found in females

One X chromosome in each cell is
randomly inactivated

Inactivated X chromosome seen as a
darkly staining area in the nucleus of a
cell

How many active chromosomes are found
in the cells of a human female?
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Barr Body
Do you see the Barr body?
Barr Bodies in Cats

Calico cat
◦ Generally all females
◦ One of several genes controlling fur color found
on X chromosome
◦ Gene on X chromosome codes for either orange
or black color
◦ Color pattern determined by random inactivation
(Barr body)
Why do you think Calico Cats are usually all female?
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Ex: Tortoiseshell (Calico) cats

animation
Calico Cat Color Inheritance
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Calico Cat

There have been instances of male Calico
cats found
◦ How could this happen?
◦ HINT: Male calico cats are sterile
Example in humans
 Anhidrotic
ectodermal dysplasia
◦ X linked mutation prevents the
development of sweat glands
◦ A woman who is heterozygous will have
patches of normal skin and patches of skin
without sweat glands
◦ Difficulty controlling body temperature
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Blood Types
ABO BLOOD TYPES
Example of codominance
 Blood type depends on the presence or
absence of certain carbohydrates
(antigens) on surface of red blood cells
 3 alleles are possible:

◦ IA :Type A Blood
◦ IB :Type B Blood
◦ i :Type O Blood
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ABO BLOOD TYPES
 IA and IB are
codominant to each other
when they are paired.

i allele is recessive to both IA and IB
If mom is homozygous for type A blood and dad is
Homozygous for Type B blood, all of the offspring will have
what blood Type?
Which blood type has no antigens?
Which blood type has both antigens?
Which blood type accepts all the other blood types?
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ABO Blood Types

Why is it important to
get the right blood type
when getting a
transfusion?
◦ Transfusion Reactions
 Immune system
(antibodies) will attack
cells that have an
antigen that the body
doesn’t recognize as
“self”
ABO Blood Types
Which square shows type O blood?
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ABO Blood Types

Blood typing is actually far more
complicated than“A”,“B”, and“O”

ABO are the MAJOR antigens

There are also MINOR antigens
◦ Rh factor: “+” or “-”
Rhesus
macaque
ABO Blood Types
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ABO Blood Types
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