Download Incomplete Dominance

Mendel was correct, but…
There are important exceptions to
most of his principles involving
dominant and recessive alleles.
Such as…some alleles are neither
dominant nor recessive.
Sometimes one trait is not completely
dominant over another. These traits
do not blend together, but each allele
has its own degree of influence. This
is known as incomplete dominance.
Incomplete Dominance
Which allele is dominant in this case?
Incomplete dominance
The phenomenon in which the
effects of both alleles are
apparent in the phenotype.
R=red
W=white
RW=Pink
»R
W
RW
RW
W
R
RW
RW
Both genes express themselves equally so you get a pink color in the petals.
However, by crossing two pink flowers
together there is a different outcome.
• There is a possibility of obtaining one
white, two pink, or one red flower.
W
R
W
WW
R
WR
WR
RR
• Neither! The heterozygous phenotype is
somewhere in between the 2 homozygous
phenotypes
Codominance
• The phenomenon in which the
effects of both alleles are
apparent in the phenotype.
Codominance
A similar situation to incomplete
dominance, however instead of
the appearance of blending of
colors, both colors are expressed.
1. Identify which traits show codominance or
incomplete dominance
a) Birds can be blue, white, or white with blue-tipped
feathers.
b) Flowers can be white, pink, or red.
c) A Hoo can have curly hair, spiked hair, or a mix of
both curly and spiked.
d) A Sneech can be tall, medium, or short.
e) A Bleexo can be spotted, black, or white.
• In fact, in most organisms, genetics is
more complicated because the majority of
genes have more than 2 alleles.
Multiple alleles
• This does not mean that an
individual can have more than 2
alleles. It only means that more
than 2 possible alleles exist in a
population.
• For example human genes for
blood type.
A single gene with 4 known
alleles that display a pattern of
dominance that can produce 4
different blood types.
Polygenic Traits
• Traits that are controlled by 2 or more genes.
EX: Eye color—many genes are used in
producing eye color. Different combinations
of alleles for these genes produce
very different eye colors.
• AND…to make things even more
interesting , many important traits
are controlled by more than one
gene.
It’s all good!
Selective Breeding
The process of selecting a few
organisms with desired traits
to serve as parents of the next
generation.
Selective Breeding
• For example, people have bred horses
that are particularly fast or strong. And
farmers have bred crops that produce
large fruit or that grow in specific climates.
Over the past 12,000 years,
dogs have been selectively
bred to produce more
than 150 breeds.