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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