Transcript Dominant, Recessive, or Neither?

Patterns of Intermediate
Inheritance
Exceptions to Mendel’s Principles
Mendel’s 3 principles provide us with an
important foundation in building our
knowledge of genetics.
However, there are many types of
inheritance patterns that do not follow the
principle of dominance.
There are several types of intermediate
inheritance patterns:
– Incomplete Dominance
– Codominance
– Multiple Alleles
– Polygenic Traits
– Multifactorial Inheritance
Co-dominance
A trait for which both alleles contribute
equally to the phenotype.
– Example: Coat color in cows and horses
– When a homozygous red cow is crossed with
a homozygous white cow they produce a
heterozygous cow that is red and white
(roan).
Genotype: CC
Genotype: WW
Genotype: CW
Practice Cross - Codominance
A horse that is roan is a blend of red and white
colors that result when a red horse is crossed
with a white horse. Red (R) horses breed true;
and white (W) horses breed true.
What is the genotype of a red horse?
–
RR
What is the genotype of a white horse?
–
WW
What is the genotype of a roan horse?
–
RW
Show the cross between two roan horses (use R and W).
What is the probability that two roan horses will have at
least one roan offspring?
–
50%
What is the probability that two roan horses will have a
white offspring?
–
25%
Incomplete Dominance
Results in a heterozygous phenotype
that is a blend of the two homozygous
phenotypes.
– Examples: mirabilis (four o’clock) plants,
coat color in horses
– When a homozygous chestnut horse is
crossed with a homozygous white horse,
they produce a heterozygous tan (palomino)
horse.
Genotype: cc
(Chestnut)
Genotype: ww
Genotype: cw
(Palomino)
Practice Cross – Incomplete
Dominance
In Four O’Clocks, the gene for red flowers (r) is
incompletely dominant to the gene for white flowers
(w).
The heterozygous condition results in pink flowers.
Red Plant Genotype?
–
rr
White Plant Genotype?
–
ww
Show the results of a cross between a Four O’Clock with red
flowers and a Four O’Clock with white flowers.
Are the F1 flowers purebred or hybrid?
–
hybrid
What is the phenotype of the F1 flowers?
–
pink
Mirabilis plants
Multiple Allelles
When a gene has more than two possible
alleles.
– Example: Rabbit Coat Color is controlled by 4
alleles - C, cch, ch, and c
CC, Ccch, Cch, Cc
ch
ch
c c ,
ch
h
c c,
ch
c c
chc or chch
cc
Practice cross: Multiple Alleles
Practice cross: In rabbits there are four different color alleles:
–
–
–
C is dominant over all of the others
cch is dominant to ch and c
ch is dominant to c
C = wild type color
cch = chinchilla color
ch = Himalayan color
c = albino
Each rabbit can inherit only two alleles. A wild colored rabbit is crossed
with an albino and in the offspring there is a Himalayan rabbit. Show
the cross.
What are the genotypes of the parents?
–
Parent one : Cch
Parent two : cc
What is the probability that they will have an offspring that is Himalayan?
–
50%
What is the probability that they will have an offspring that is albino?
–
0%
What is the probability that they will have an offspring that is wild
colored?
–
50%
Polygenic
A trait that is controlled
by the interaction
between 2 or more
genes.
– Examples: skin color, eye
color, height, hair color
– Results in a continuum of
expressed phenotypes.
Multifactorial Inheritance
The phenotype is a result of an interaction between your
genotype and certain environmental factors.
The expression of most all genes is influenced by
environmental conditions.
Examples:
– Diabetes
– Height
– Heart Disease
Can inherit a predisposition to all of these diseases/characteristics.
Their development (phenotype) is influenced by environmental
factors such as proper nutrition, exercise, quality medical care, etc.
Examples in plants:
In many plants, the
presence of light
triggers the
production of
chloroplasts.
Chemicals that
stimulate
germination are only
produced in the
presence of certain
temperatures.
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