Transcript ABO Blood Types

Mendel’s Peas were ideal for
learning about inheritance, but
they do not represent the norm…
• Traits in pea plants are determined by just
two alleles
• In peas, one allele is clearly dominant &
the other is clearly recessive
• However, things aren’t always this clearcut and simple in the world of genetics.
What if Mendel looked at mice?
 If a female black mouse and a male
white mouse were crossed, what will
the offspring look like?
- 100% are GREY
 If the F1 offspring were crossed, what
will there offspring look like?
- 25% black
- 50% grey
- 25% white
Incomplete Dominance
• A cross between two organisms with
different traits results in an offspring with
a third phenotype that is a blending of the
parental traits.
• It’s like mixing paints:
– Red + White = Pink
– Red does not totally block (dominate) white,
we end up with something in-between.
Inheritance in Snapdragons
Codominance
• Similar to incomplete dominance in that
there is a 3rd phenotype
• In COdominance, the “recessive” and
“dominant” alleles appear together in the
phenotype of hybrid organisms.
• Red x White = red & white
Let’s look at cattle….
This cow resulted from a cross between a cow
with red fur (RR) and a cow with white fur (WW)
This is called ‘roan’ fur; red & white fur together
(RW)
Sickle Cell Anemia: Codominance &
Incomplete Dominance
Normally, a person inherits two copies of the gene that produces betaglobin, a protein needed to produce normal hemoglobin (hemoglobin A,
genotype AA). A person with sickle cell trait inherits one normal gene
and one abnormal gene encoding hemoglobin S (hemoglobin genotype
AS).
HbAHbA - normal
HbSHbA – carriers or sickle cell trait
Red blood cells “sickle” and break apart when there is a low
[O2](incomplete dominance of A allele; A is not completely expressed all
the time); Overall lower concentration of hemoglobin all the time
(codominance = both normal and mutant alleles expressed)
HbSHbS – sickle cell anemia
All red blood cells sickle shaped; very painful; anemia ; Requires transfusion
Sickle Cell Anemia and Natural Selection
• Carriers for sickle cell have an advantage in tropical
locations where malaria is prevalent.
• Carriers have protection from malaria.
• Malaria is a blood-borne disease transmitted by
mosquitoes.
Polygenic (Multifactorial) Traits
• Phenotype is determine by more than one
gene
• Often results in gradations, where each
gene has an additive effect
Ex) If 10 gene loci are turned on plant will be
20cm tall, if only 5 loci are turned on plant
will be 10cm tall
• Results in a bell-shaped curve
– Skin color & Height are examples in humans
Phenotype Distribution:Polygenic Traits
Multiple Alleles
• More than 2 alleles for a particular trait
KEY
C = full color; dominant
to all other alleles
cch = chinchilla; partial
defect in pigmentation;
dominant to
ch and c alleles
ch = Himalayan; color in
certain parts of the
body; dominant to
c allele
chhc
ch,cCc
h
ch
AIbino:
Chinchilla:
Himalayan:
cc CC,
cc
c,hCc
, or
cch
c,hhor
cch
c
Full color:
, or
Cc
c = albino; no color;
recessive to all other
alleles
ABO Blood Types
• In addition to having multiple alleles, ABO
blood type also exhibits codominance
• ‘IA’ & ‘IB’ are codominant
(A and B = codominant)
• ‘i’ is recessive
(O is recessive to A and B)
ABO Blood Typing
Genotype
Blood Type
IA IA or IA I
(AA or AO)
IB IB or IB I
(BB or BO)
IAIB
A
B
AB
AB
ii
OO
O
What does your ABO blood type mean?
 Remember the ‘flags’
on our cell membranes?
They help cells to
recognize each other.
 Some of those flags
‘announce’ your blood
type. We call these
flags antigens
Blood
Type
A
A
B
Antigen
B
AB
A and B
O
none
ABO Blood Transfusions
Blood
Type
A
A or O
B
B or O
AB*
O*
Can receive:
All (Universal
recipient)
O (Universal donor)
Summary of ABO Blood Types
ABO Blood Type Summary
Rh Factor
• Blood can also be categorized as + or –
• This refers to the presence (dominant) or
absence (recessive) of the Rh antigen
Phenotype Genotype(s)
Rh+
Rh-
Rh+/Rh+ or
Rh+/RhRh- /Rh-
Antigen
present
Not present
Rh Factor Compatability
Mom is Rh- and baby is Rh+
If baby’s blood mixes with
mom’s, mother will make Rh
antibodies.
If the next pregnancy is a Rh+
baby, antibodies will cross the
placenta and attack baby’s red
blood cells (hemolytic disease)
Rh factors must also be taken
into account in blood
transfusions.
Rh- cannot get Rh+ blood
Chromosomal Theory of Inheritance
• This theory states that genes occupy specific loci on
chromosomes and it is the chromosomes that undergo
segregation and independent assortment during meiosis.
Gene Linkage & Mapping Chromosomes
Genes that are farther apart are more likely
to cross over.
Use frequency of crossover events
(recombinant chromosomes to map gene
locations.
May be separated (Not
inherited together)
Get inherited together
(linked)
http://www.nature.com/scitable/topicpage/thomas-hunt-morgan-geneticrecombination-and-gene-496
Gene Linkage & Mapping Chromosomes
• According to the chromosomal theory of inheritance, genes on the
same chromosome are more likely to be inherited together
• Crossing over helps to increased variation, but the closer two
genes are on a chromosome the more likely they are to be “linked”
• The frequency of crossing over between two genes can be used to
estimate the relative positions of genes on chromosomes
• http://www.ndsu.edu/pubweb/~mcclean/plsc431/linkage/
linkage1.htm
• http://www.nature.com/scitable/topicpage/thomas-huntmorgan-genetic-recombination-and-gene-496
Sex Chromosomes & Autosomes
• Recall that two of the 46 human chromosomes
are known as sex chromosomes, because they
determine the individual’s sex.
– Females have two copies of an X chromosome.
– Males have one X chromosome and one Y
chromosome.
• The remaining 44 chromosomes are known as
autosomal chromosomes or autosomes.
Sex-Linked Genes
• Located on one of the
sex chromosomes
(X or Y)
• Since the X
chromosome is
longer, it has many
genes not found on
the Y chromosome.
• Most sex-linked
genes are X-linked
genes.
Sex-Linked Genes
X-Linked Inheritance
• Examples:
– Hemophilia
• The protein necessary for normal blood clotting is missing
– Colorblindness
• Defective version of one or all of the 3 genes responsible for
color vision
– Male Pattern Baldness
• Hair loss
– Duchenne Muscular Dystrophy
• Weakening and loss of skeletal muscle
• These traits are recessive & more common in males.
Why?
Possible Inheritance of Colorblindness Allele
Complete the following sex-linked crosses:
Eva and Paul just had a son,
Michael. Paul has normal
color vision, but Eva’s father
was colorblind. What is the
likelihood that Michael is
colorblind?
Laura and Steve are expecting
their first child. They are
concerned about the chances
their child might be
hemophiliac because Steve is
hemophiliac and Laura’s father
is hemophiliac. What is the
probability of Laura and Steve
having a hemophiliac child?
Complete the following pedigrees.
Which is for a sex-linked trait? How do you know?
Pleiotropy
One gene 
one
polypeptide
but…
One gene can
affect
MULTIPLE
traits/conditions
(Pleiotropy)