Download File

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:
– Co-dominance
– Multiple Alleles
– Incomplete Dominance
– 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: RR
Genotype: WW
Genotype: RW
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?
R
W
R
RR
RW
W
RW
WW
– 50%
What is the probability
that two roan horses
will have a white
offspring?
– 25%
Multiple Alleles
When a gene has more than two possible
alleles.
ONLY TWO alleles are inherited.
– Example: Rabbit Coat Color is controlled by 4
alleles - C, cch, ch, and c
CC, Ccch, Cch, Cc
cchcch, cchch, cchc
chc or chch
cc
Practice cross: Multiple Alleles
Practice cross: In rabbits there are four
different color alleles:
–
–
–
–
C is dominant over all
cch is dominant to ch & c
ch is dominant to c
C is recessive to all
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 between a wild type and
albino rabbit that has a Himalayan baby.
What are the genotypes of
the parents?
C
ch
c
Cc
cch
c
Cc
cch
– Parent one : cc
– Parent two : Cch
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%
Mult. Alleles
&
Co-dominance
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 red
Four O’Clock and a white Four O’Clock.
r
r
w
rw
rw
w
rw
rw
Are the F1 flowers
purebred or hybrid?
– hybrid
What is the
phenotype of the F1
flowers?
– pink
Snapdragons
Mirabilis plants
Polygenic
Humans
& Plants
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.
Enviro
Factors
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.
http://www.dkimages.com/discover/previews/874/30020399.JPG
Review
of Terms