Download Chapter 12

Chapter 12: Non-Mendelian
Inheritance Patterns
Mrs. Geist, Biology, Spring 2010-2011
Intermediate/Incomplete Dominance
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Neither allele is dominant.
The heterozygotes have a phenotype that is intermediate
between the phenotype of two homozygotes.
This does not support the Blending Theory.The parent
phenotypes can reappear in the F2 generation.
Incomplete Dominance
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Example 1: Carnations are
available as red flowers
(RR), white flowers (WW),
or pink flowers (RW).
Determine the probable
phenotypic outcomes for
the following crosses.
SHOW ALL STEPS!
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Red x pink
Pink x white
Red x white
Incomplete Dominance Practice
Example 2: In horses, B is the allele for brown hair color. W
is the allele for white hair. A heterozygous horse would
be a palomino (golden color and blonde tails).
 Write the genotype for each horse that is
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Brown
White
Palomino
Write the phenotypes for each horse that is
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Homozygous HB
Homozygous HW
Heterozygous
Incomplete Dominance Practice
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Determine the probable phenotypic outcomes for the
following crosses. SHOW ALL STEPS!
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White horse x brown horse
Palomino x palomino
Palomino x brown
Codominance
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A heterozygote expresses
both traits.
The individual’s
phenotype, is not
intermediate but rather
shows the separate traits
of both alleles.
Example 1: In cattle, R is
the gene for red hair, and
W is the gene for white
hair. A heterozygous cow
would be roan (red &
white spots).
Top left: white cow. Top right: red cow.
Bottom: roan cow (red & white spots).
Codominance Practice
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Write the genotype for each cow that is
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Write the phenotypes for each cow that is
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Red
White
Roan
Homozygous R
Homozygous W
Heterozygous
Determine the probable phenotypic outcomes for the
following crosses. SHOW ALL STEPS!
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Red cow x white bull
Roan cow x white bull
Roan x roan
Codominance Practice
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Example 2: One strain of chicken expresses a codominant
trait for feather color. Black feathers (BB), white feathers
(WW) or Erminette/speckled feathers (BW). Determine
the probable phenotypic outcomes for the following
crosses (heterozygous). SHOW ALL STEPS!
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Speckled x speckled
White x black
Black x speckled
Multiple Alleles
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For many genes, several alleles (versions of the gene)
exist in the population for a given trait, making the
possible number of genotypes and phenotypes greater.
Example 1: In humans, blood type is determined by more
than two alleles (IA, IB, and i). IA and IB are dominant over I,
but IA and IB are codominant to each other.
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Type A blood: IAIA or IAi
Type B blood: IBIB or IBi
Type AB blood: IAIB
Type O blood: ii
Multiple Alleles Practice
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Write the phenotypes for each person that is
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IAIA
IAi
IAIB
Ibi
Determine the probable phenotypic outcomes for the
following crosses. SHOW ALL STEPS!
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AB x O
AB x AB
A x O (show all possible)
A x B (show all possible)