Incomplete and
Co-Dominance
Incomplete Dominance
• One allele is not
completely
dominant over the
other.
• The heterozygous
phenotype is inbetween the
homozygous
phenotypes.
Incomplete Dominance
If you cross a
RED flower with
a WHITE flower,
you will get a
PINK flower.
NOTICE:
the RED genotype is RR
the WHITE genotype is WW
the PINK genotype is RW
Let’s Practice!
Cross a BLACK chicken (BB) with a WHITE chicken
(WW). These alleles show INCOMPLETE
DOMINANCE.
What
percent
is black?
White?
Gray?
W
W
B
B
BW
BW
BW
BW
Black: 0%
White: 0%
Gray: 100%
Let’s Practice!
Cross a BLACK chicken (BB) with a WHITE chicken
(WW). These alleles show INCOMPLETE
DOMINANCE.
What is the
genotype and W
phenotype
of the F1
generation?
W
B
B
BW
BW
BW
BW
Genotype:
BW
Phenotype:
Gray
Let’s Practice!
What would the cross look like if you crossed two
GREY chickens (BW). These alleles show
INCOMPLETE DOMINANCE.
What is the
genotype and
phenotype of
the F2
generation?
B
W
B
W
BB
BW
BW
WW
Genotype:
1 BB
1 WW
2 BW
Phenotype:
1 Black
1 White
2 Gray
Mrs. Smith and Ms. K’s Memory Trick
INcomplete is
INbetween
Co-Dominance
• Both alleles contribute to the phenotype.
• For Example: In chickens, the allele for black
feathers is co-dominant with the allele for
white feathers. These chickens will have BOTH
black and white feathers.
Let’s Practice!
Cross a Black chicken (BB) with a White chicken
(WW). These alleles show CO-DOMINANCE.
How many
chickens in the W
F1 generation
are completely
black? White?
Black and
W
white?
B
B
BW
BW
BW
BW
Black: 0%
White: 0%
Both: 100%
Let’s Practice!
Cross a Black chicken (BB) with a White chicken
(WW). These alleles show CO-DOMINANCE.
B
What is the
genotype
W
and
phenotype
of the F1
generation?
W
BW
BW
B
BW
Genotype:
BW
BW
Phenotype:
Black and
white or
checkered.
Let’s Practice!
Cross two Black and White (checkered) chickens
(BW). These alleles show CO-DOMINANCE.
B
List all
possible
B
genotypes
and
phenotypes
of the F2
generation. W
BB
BW
W
BW
WW
Genotype:
1 BB
1 WW
2 BW
Phenotype:
1 Black
1 White
2 Checkered
Mrs. Smith and Ms. K’s Memory Trick
COdominant alleles
COllaborate together
If you need more help…
READ PAGE 272