Transcript Incomplete Dominance

Incomplete Dominance
What 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.)
How 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.
Practice 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.
Complete the parent cross
BY
BY
BY
BY
If the mother
is a yellow lab
and dad is a
black lab all
offspring are
chocolate labs
Cross two offspring that are chocolate
labs
BB
BY
BY
YY
BB = black lab
BY =
chocolate lab
YY = yellow
lab
What did you notice?
• You must have a key for the homozygous
parents (BB = black) (
)
• You must have a key for the heterozygous
offspring (
, not black or
)
• You should notice that the heterozygous
form is not dominant but a blending or “in
between” trait.
Now 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.