Download Incomplete Dominance

Chapter 11.3
Other Patterns of
Inheritance
Four exceptions to Mendel’s principles
Incomplete
Dominance
Polygenic
Traits
Codominance
Multiple
Alleles
In most organisms, heredity is more
complicated than Mendel realized
Incomplete Dominance-
Some alleles are neither dominant NOR
recessive!!
Incomplete dominance Continued
For Example:
Four O’Clock
Flowers
Heterozygous type lies
somewhere between the
2 homozygous typesIT’s A BLEND
Incomplete Dominance Con’t
Heterozygous type lies somewhere between the
2 homozygous types- A BLEND!!
Red + White =
Pink
Co-dominance
Phenotypes produced by both alleles are
clearly expressed
NOT BLENDED! TRAITS STAY DISTINCT AND UNIQUE
BOTH TRAITS
EQUALLY STRONG
In some chickens, the gene for feather
color is controlled by co-dominance. The
allele for black is B and the allele for white
is W. The heterozygous, BW, phenotype is
known as erminette, or speckled.
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Erminette chickens- examples of CODOMINANCE- both traits show up distinctly
Other examples of Co-dominance
Ie: In humans, gene for protein that controls cholesterol
levels in the blood
Ie: Roan cows- A white cow and red
bull makes red and white spotted
offspring, also known as "roan”.
"What is the difference between co-dominance and
incomplete dominance?"
Co-dominance happens when there are two dominant
alleles for a trait and they are both shown.
For example, a red and white flower would make a
striped flower. A white cow and brown cow makes a
brown and white spotted cow, also known as "roan”.
Incomplete dominance happens when there are two
dominant alleles for a trait and they are blended (mixed).
For example, a red flower and a white flower would make
a pink flower.
Multiple Alleles
Many genes exist in several different forms, so they are said to
have multiple alleles.
Multiple Alleles
Continued
For example: coat color in
rabbits, there is ONE gene
with at least FOUR different
alleles
Multiple Alleles Continued
Another Example:
Human blood type
POLYGENIC TRAITS
Traits controlled by 2 or more genes
Many traits are produced by interaction of several genes
• For example: at least 3 genes control reddishbrown pigment in eyes of fruit flies
Many traits are produced by interaction of several genes
• For example: more than 4 genes control
skin color in humans
Many traits are produced by interaction of several
genes
• More examples of Polygenic traits: Hair and
eye color in humans
•
http://www.allaboutvision.com/conditions/eye-color-chart.htm
Genes and the Environment
Environmental conditions (internal
or external) can affect gene
expression
Temperature affecting butterfly color
Pontia occidentalist,
from western North
America is light in
color when emerges
in the summer, and
darker in color when
it emerges in the
spring p.321
Genes and the
environment:
another example…
gene for male
pattern baldness is
found in both males
and females, but the
male hormones
TRIGGER it.
Internal environment & genes
Review: Four exceptions to Mendel’s principles
Incomplete
Dominance
Polygenic
Traits
Codominance
Multiple
Alleles
In most organisms, heredity is more
complicated than Mendel realized
Other patterns of
What’s
Your
Message?
inheritance