With incomplete dominance a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits Lets imagine that Labrador retrievers yellow black and chocolate demonstrate incomplete dominance when it comes to ID: 929514
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Slide1
Incomplete Dominance
Slide2What is incomplete dominance?
With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a
third phenotype
that is a
blending
of the parental traits
.
Let’s imagine that Labrador retrievers, yellow, black and chocolate, demonstrate incomplete dominance when it comes to the color of their coats. (In reality, coat color in this breed is controlled by two different genes, thus this is just a fictitious example.)
Slide3How does incomplete dominance work?
When the phenotype of the
heterozygous
is
intermediate between
the two
homozygous
.
Neither allele is dominant/recessive over the other. Neither allele will express itself---
therefore it is very important to make a key to determine the differences between the
heterozygous
and
homozygous
state.
Slide4Practice Incomplete dominance.
EX: Labrador Retriever dogs.
Yellow labs
Black labs
Chocolate labs
When working these problems it becomes essential to make a
key
Yellow lab(YY)
Black lab (BB)
Chocolate lab (BY)
The heterozygous offspring is a
blend
of the parents.
Slide5Complete the parent cross
BY
BY
BY
BY
Y
Y
B
B
If the mother is a yellow lab and dad is a black lab all offspring are chocolate labs
Slide6Cross two offspring that are chocolate labs
BB
BY
BY
YY
Y
Y
B
B
BB = black lab
BY = chocolate lab
YY = yellow lab
Slide7What did you notice?
You must have a key for the homozygous parents (
BB = black
) (
YY = yellow
)
You must have a key for the heterozygous offspring (
BY = chocolate, not black or yellow)You should notice that the heterozygous form is not dominant but a blending or “in between” trait.
Slide8Now you try…..
Cross a Red Snapdragon flower with a White Snapdragon flower.
Set up the Punnett Square and give me both
phenotype
and
genotype
Ratios.
x
Slide9R
R
W
W