Quiz 7D
Variations in Mendel's Theories
Variations in Mendel's Theories
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Incomplete dominance
Codominance
Multiple gene inheritance
Sex-Linked traits
Incomplete dominance
a type of inheritance in which the genes
expressing a particular characteristic are
neither dominant or recessive; two traits
combine or blend together to produce a
different trait (a blend of two traits)
(when offspring of two homozygous
parents show an intermediate phenotype)
Incomplete dominance
example: flower color in snapdragons &
four o’clock flowers
Codominance
In codominance the dominant and the
recessive traits are both expressed.
Example:
roan cattle
Codominance
In incomplete dominance neither allele is
fully dominant. This is different from
codominance, in which both alleles are fully
expressed, resulting in organisms that display
the characteristics of both parents.
Codominance
In codominance, both alleles are expressed
independently and are uniquely recognizable.
multiple gene inheritance
multiple gene inheritance (also called
Polygenic Inheritance)- two or more genes
producing a single trait (examples: hair
color, skin color, eye color, height,
intelligence, body build, etc.)
How to work incomplete
dominance problems.
purebred red X purebred white carnations
How to work incomplete
dominance problems.
Step 1: possible pheotypes and genotypes
Pheno Geno
red
rr
white ww
pink rw
• use two different
letters to represent genes
• use lower case letters
purebred red X purebred white carnations
How to work incomplete
dominance problems.
Step 2: parent genotypes
r
r
w
w
purebred red X purebred white carnations
How to work incomplete
dominance problems.
Step 3:
fill in possible
genotypes of
offspring
r
r
w wr wr
w w r wr
purebred red X purebred white carnations
How to work incomplete
dominance problems.
Step 4:
Genotipic ratio
Phenotipic ratio
red:white:pink
rr:ww:rw
r
r
w wr wr
w w r wr
0:0:4
purebred red X purebred white carnations