Download INCOMPLETE DOMINANCE

Incomplete Dominance,
Codominance and Multiple
Alleles
INCOMPLETE DOMINANCE
Incomplete Dominance- Pattern of gene
expression in which the phenotype of a
heterozygous individual is intermediate
between those of the parents.
• Cases in which one allele is not completely
dominant over another.
Example: Snapdragons
and Carnations
Incomplete Dominance- F1 generation
Incomplete Dominance- F2 generation
CODOMINANCE
Codominance- The condition in which both
alleles in a heterozygous organism are
expressed.
• BOTH alleles contribute to the phenotype.
• The two alleles don’t blend, but are rather
both present in the offspring.
Examples- Checkered Chickens, Roan Horses,
Roan Cows, Variegated Clover.
Codominance
Black
Checkered
White
White chicken
Black chicken
W
W
B
B
BW
BW
Checkered
BW
Checkered
Checkered
BW
Checkered
Roan Horse
http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT
Roan Cattle
http://www.ccs.k12.in.us/chsteachers/BYost/Biology%20Notes/CH11notescoincompletedom_files/image004.jpg
Variegated Clover
http://3.bp.blogspot.com/_zUPrgMM5tUg/SSVdrs59_uI/AAAAAAAAAA8/qJGjG2nZPhk/s200/codominance.GIF
Multiple Alleles
Multiple Alleles- Genes which have more than
two alleles.
 It is common for more than 2 alleles to control
a trait in a population
 Multiple alleles can only be studied in
populations since each individual only has 2
alleles for a trait.
 Examples: human blood types, fruit fly eye
color, coat color in rabbits: C, cch, ch, and c.
Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Coat Color of Rabbits
Chinchilla
Albino
Light gray
Dark gray
Himalayan
ABO Blood Type
• ABO blood type in
humans is determined by
three alleles:
IA IB i
• IA and IB are codominant
alleles.
• Both IA and IB are
dominant to the allele i.
Blood
Genotype
Type
IAIA
IAi
A
A
IBIB
B
IBi
B
IAIB
ii
AB
O
Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Multiple Alleles
Blood groups in
humans
ABO blood groups
have three forms of
alleles.
Donor-recipient compatibility
Recipient
Type
A
B
AB
O
A
Donor
B
AB
O
= Unsafe
transfusion
= Safe
transfusion
© 2007 Paul Billiet ODWS
Note:
• Type O blood may be transfused into all the
other types = the universal donor.
• Type AB blood can receive blood from all the
other blood types = the universal recipient.