Incomplete Dominance
• alleles are equally dominant
• together produce a new phenotype
(different from both parents)
• result is blending
• Example - Snapdragon flower colour
• All of the F1 generation will display
the blended phenotype
Codominance
• type of incomplete dominance
• both alleles are expressed at the
SAME TIME
• Example - Shorthorn cattle hair colour
Red bull crossed with a White cow
c m
Q ui kTi e™ and a
decom pr essor
s c
ar e needed t o see t hi pi t ur e.
• ‘Roan’ is the name of the new trait
The Parent phenotypes reappear in the
F2 generation
Example: Blood type
• The alleles (genes) become proteins
that attach to the surface of blood
cells
• The immune system attacks any blood
cells that have proteins that body
doesn’t have
• 2 possible proteins - known as blood
types A and B (alleles IA and IB)
• A and B are codominant, so they will
both be expressed if present
• Also possible to not have either of these
on the surface of a blood cell
• Allele IO is recessive and must be
homozygous for this trait to have
phenotype O
• An individual carries two alleles for this
trait, which can mean none, one or two
types of proteins on the blood cell
QuickTime™ and a
decompressor
are neede d to see this picture.
• Possible genotypes for phenotypes:
IAIA, IAIO IBIB, IBIO
QuickTime™ and a
decompressor
are neede d to see this picture.
IAIB IOIO
• Example: A person’s genotype is IBIO.
What is their phenotype?
- Blood type B
• Example: Mom has type A, and dad is
type AB. What are the possibilites
for the children’s genotype?
- Type A: IAIA, IAIO
- Type AB: IAIB
- Type B: IBIO
• Try this question:
Jill is blood Type O. She has two older
brothers with blood types A & B. What are
the genotypes of her parents for this trait?
- if her brothers are A and B, the IA
and IB alleles must be present in the
parents
- Jill is IOIO, and has to get one from
each parent
- Parents must be IAIO and IBIO