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

Codominance W

hite

chi

cken

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 compatibilityRecipie

nt

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