Transcript 9 Incomplete Dominance PPT

June 2, 2016
June 2, 2016

Some traits do not have a clear dominant and
recessive allele. In this case, BOTH alleles are
expressed. This is called codominance
because BOTH alleles act like they are
dominant.
June 2, 2016

Sometimes there are more than two alleles
possible for a trait. This can lead to more
possible genotypic and phenotypic ratios…
June 2, 2016
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.
Its like mixing paints, red + white will make pink.
Red doesn't totally block (dominate) the white,
instead there is incomplete dominance, and we
end up with something in-between.

How do we work these new types of
problems?
A.
B.
We can still use the Punnett Square to
solve problems involving codominance
and incomplete dominance.
We just need to use a capital letter for
EACH trait (Two different letters instead of
one letter in capital and small case)
Ex- What are the genotypes for each of the
flowers types we used in the earlier
example?
White flower = WW
Red flower = RR
Pink flower = RW
So the cross from the example we used up
above would look like this:
R
R
W
W
RW
RW
RW
RW
100% RW
100% Pink
flowers
June 2, 2016
In polygenic inheritance there is more
than one gene responsible for a trait.
This usually results in continuous
variation.
 In humans, for example, traits such as
height, shape, weight, color, and
metabolic rate are governed by the
cumulative effects of many genes


Polygenic traits are recognizable by their
expression as a continuous variation of small
differences. The results form a bell shaped
curve, with a mean value & extremes in either
direction.
Complete both practice problems in your notes with the people sitting around you.
NOTE: SpongeBob loves growing flowers for his pal Sandy! Her favorite flowers,
Poofkins, are found in red, blue, and purple. Use the information provided and
your knowledge of incomplete dominance to complete each section below.
a. Write the correct genotype for each color if R represents a red gene and B
represents a blue gene.
Red - _____ Blue - ______ Purple - _____
b. What would happen if SpongeBob crossed a Poofkin with red flowers with a
Poofkin with blue flowers? Complete a Punnett square to determine the ratio of
genotypes and ratio of phenotypes for the offspring.
c. What would happen if SpongeBob crossed two Poofkins with purple flowers?
Complete a Punnett square to show the ratio of genotypes and ratio of phenotypes
for the offspring.
Be prepared to share your answers!!