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Incomplete Dominanceand
Codominance
copyright cmassengale
Given a red flower and a white flower….
Which is dominant?Do a test cross
X = ?
X =
!
Incomplete Dominance
• Neither allele is dominant or recessive to tothe other.
• A heterozygous phenotype – A mixture or blended trait results– Blended trait does not “look” like either
homozygous phenotype• Two different capital letters are used
– Letters written in alphabetical order
Four-o’ clock flowersINCOMPLETE DOMINANCE
– Neither Red (R) – nor White (W) is dominant
A Homozygous red flower (RR) is crossed with a homozygous white flower (WW),
The alleles blend in the hybrid (RW) producing pink flowers
RR x WW = RW
Andalusian Chickens
• Incomplete dominance• Neither Black (B) nor
White (W) is dominant
BB x WW = BWThe offspring of a black feathered chicken (BB)
and a white feathered chicken (WW) are blue (BW) – BLUE HEN!!
X =
RR x WW = RW
X = ?
!
Codominance
• Both alleles are dominant • Neither one is recessive.• Heterozygous phenotype:• both phenotypes show (are expressed) at the
same time.• Two different capital letters are used
– Letters written in alphabetical order
X =
RR x WW = RW
Shorthorn Cattle
Co- dominance• Homozygous red (RR)• Homozygous white (WW)
The offspring of will have both red and white hairs (RW)
The offspring are heterozygous and called “roan”
http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT
Roan Horse
Explain the difference:incomplete dominance co-dominance
Neither dominant or recessive to the other
Both are dominant
Heterozygous –blended trait
Heterozygous – both traits show at the same time
Doesn’t look like either parent but is in between
Loos like both homozygous parents