Incomplete Dominance, Codominance and Multiple Alleles
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Incomplete Dominance, Codominance and Multiple
Alleles
INCOMPLETE DOMINANCEIncomplete 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: Snapdragonsand Carnations
Incomplete Dominance- F1 generation
Incomplete Dominance- F2 generation
CODOMINANCECodominance- 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.
B B
W
W
BW BW
BW BW
CodominanceW
hit
e c
hic
ken
Black chicken
Checkered
Checkered Checkered
Checkered Checkered
Black White
http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT
Roan Horse
Roan Cattle
Variegated Clover
http://3.bp.blogspot.com/_zUPrgMM5tUg/SSVdrs59_uI/AAAAAAAAAA8/qJGjG2nZPhk/s200/codominance.GIF
http://www.ccs.k12.in.us/chsteachers/BYost/Biology%20Notes/CH11notescoincompletedom_files/image004.jpg
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.
Complex Inheritance and Human Heredity
Coat Color of Rabbits
Light gray
Dark gray Himalayan
Albino
Chinchilla
11.2 Complex Patterns of Inheritance
Chapter
11
GenotypeBlood
Type
IAIA A
IAi A
IBIB B
IBi B
IAIB AB
ii O
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.
Complex Inheritance and Human Heredity
Multiple Alleles
Blood groups in humans
ABO blood groups have three forms of alleles.
11.2 Complex Patterns of Inheritance
Chapter
11
Donor-recipient compatibilityRecipient
Type A B AB O
A
Donor B
AB
O
= Unsafe
transfusion
= Safe
transfusion
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.
© 2007 Paul Billiet ODWS
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