Genetics:
Multiple Alleles
Biology 12
Joke of the day:
Multiple Alleles
 Many
genes have
more than two
alleles
 An individual does
not have more than
two alleles for each
trait but different
individuals can
have different pairs
of alleles when
multiple alleles exist
Example: Multiple Alleles
 Human
blood type is controlled by three
alleles : IA, IB and i.
 Alleles IA and IB are dominant over i
 IA and IB are codominant
Phenotype (blood type)
Genotypes
A
B
AB
O
IA IA or IAi
IB IB or IBi
IA IB
ii
http://www.pennmedicine.org/health_info/images/19450.jpg
Problem: Multiple Alleles
 Show
the cross between a mother who has type O
blood and a father who has type AB blood.
GENOTYPES:
- IAi (2) IBi (2)
- ratio 1:1
i
IA
PHENOTYPES:
B
I
- type A blood (2); type B
blood(2)
- ratio 1:1
i
IAi
IAi
IBi
IBi
Problem2: Multiple Alleles
 Show
the cross between a mother who is
heterozygous for type B blood and a father
who is heterozygous for type A blood.
GENOTYPES:
-IAIB (1); IBi (1);
IAi (1); ii (1)
- ratio 1:1:1:1
PHENOTYPES:
-type AB (1); type B (1)
type A (1); type O (1)
- ratio 1:1:1:1
IA
i
IB
IAIB
IBi
i
IAi
ii
http://duongchan.files.wordpress.com/2007/05/abobloodsystem.jpg
http://image.wistatutor.com/content/feed/tvcs/blood_type5B15D.jpg
Rhesus Factor
 The
Rhesus factor, also
known as the Rh factor,
gets its name from
experiments conducted
in 1937 by scientists Karl
Landsteiner and
Alexander S. Weiner.
 Involved
Rabbits which
when injected with the
Rhesus monkey’s red
blood cells, produced an
antigen present in the red
blood cells of many
humans
http://content9.clipmarks.com/blog_cache/latimesblogs.latimes.com/img/E0C83714-56E5-4757-B9F1-604FCE5643C3
Rhesus Factor:
 The
Rhesus factor is an
antigen (a protein) that
exists on the surface of red
blood cells.


If a person has either two (+)
genes for Rh or one (+) and
one (-) Rh gene, they will test
Rh(+).
A person will be negative
only if they have 2 (-).
Relevance of Rh Factor & ABO Typing?
 It
is very important in terms of babies
 Example:
An Rh(-) mother has a Rh (+) baby,
she will make antibody against the Rh(+) fetus
To do:
 Blood
type WS
 Genetics: Multiple Allele Traits WS