blood type and sex linked inheritance with sex...a real problem: mom is type b, dad is type o …...
TRANSCRIPT
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Blood Type and Sex Linked Inheritance
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The Classic Example of Codominance in
Humans is BLOOD TYPE
Gene that controls ABO blood type codes for an enzyme that makes a glycolipid on blood cells
Two alleles (IA and IB) (call them “A” and “B”) are codominant
Third allele (IO) (call it “O”) is recessive to A and B
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Possible Genotypes for
Blood Types
If the Phenotype: A
Genotype(s): AA, AO
If the Phenotype: AB
Genotype(s): AB
If the Phenotype: B
Genotype(s): BB,BO
If the Phenotype: O
Genotype(s): OO
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Your blood type is determined by A and/or B proteins
on red blood cell surfaces
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Blood Tests are done by adding antibodies
to the sampleWhich blood type clots with both anti-A and anti-B? _____
Which blood type
AB
Which blood type doesn’t clot with anti-A or anti-B? _____
• Do you know what
YOUR blood type
is?
O
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The Rhesus Factor
You are either R(+) or R(-) for the
Rhesus Protein A problem for Rh (-) moms …
•What if baby is Rh (+)?
• Doctor can give Mom a shot (Rhogam, at about 28 weeks) that
removes or hides R(+) cells from Mom’s bloodstream
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A Real Problem:
Mom is Type B, Dad is Type O … Baby is Type AB. Is
this possible?
•Cross: ____ X ____BOMOM
OORemember, when
in doubt,
heterozygous is
more likelyB O
O
O
BO
BO
OO
OO
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Sex Chromosomes:
the 23rd pair in humans
All others (1-
22) are
called
autosomesautosomes
Boy Girl
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The Sex Chromosomes
The “X” Chromosome
Has essential genes
Can’t live without it!
Female 23rd pair = XX (one usually deactivated)
����
The “Y” Chromosome
Few genes
Determines if testes develop
Male 23rd pair = XY
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What’s the probability of having a boy or girl?
X X
XX
XY
XX
XYY
X
50%
50%
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Sex-Linked (X-Linked) Traits
Sex-Linked traits are usually found on the X (not Y) chromosome (“X-linked”)
Males are affected or not, no heterozygotes… WHY, do you think?
����
heterozygotes… WHY, do you think?
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Some X-Linked Traits:
Haemophilia (missing clotting enzymes)
Colorblindness
“Male-pattern” baldness“Male-pattern” baldness
Most are recessive
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Haemophilia
Ability of blood to clot is impaired.
The main treatment for hemophilia is called replacement therapy—giving or replacing the clotting factor that’s too low or missing.
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“The Royal Disease”
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A haemophiliac man marries a healthy woman. What is the probability that they will have any haemophiliac children?
0%All sons healthy
All daughters carriers
0%
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Colorblindness
Red-green colorblindness-
red and green are perceived as identical.
Affects:
1 in 10 males in the US
1 in 100 females in the US
Remember: Males have just one X chromosome. All X-linked alleles are expressed in males.
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A man with normal vision marries a colorblind woman. What is the probability that they will have a
colorblind SON?
•Cross: ____ X ____XcXc
MOM
XYRemember, Mom
only shows if she is
homozygous!
Xc Xc
����
X
Y
XcX
XcY
XcX
XcY
Focus only on SONS
(not daughters)!
100%(2/2) SONS
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What do you see?
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A bald man marries a woman whose father was bald. What is the probability that they will have a SON with male-
pattern baldness?
•Cross: ____ X ____XbXMOM
XbYIf Mom’s father
was bald, then he
must have passed
that X to her!Xb X
����
Xb
Y
XbXb
XbY
XbX
XY
THE TRICK: Focus only on SONS
(not daughters)!
50%(1/2) SONS
XbY
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