Class Notes
Intermediate
Inheritance patterns
Questions/Main
Idea:
What is codominance?
Practice codominance
crosses:



What is the genotype of a
red horse?
What is the genotype of a
white horse?
What is the genotype of a
roan horse?
Name: _______________________________________
Period:_______________________________________
Date: _______________________________________
Notes:
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).
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.
RR
WW
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?
What is the probability
that two roan horses will
have a white offspring?
25%
WW
RR
RW
RW
WW
50%
RW
What are multiple
alleles?
When a gene has more than two possible alleles.
– Example: Rabbit Coat Color is controlled by 4 alleles –
C, cch, ch, and c
Practice multiple allele
crosses:
In rabbits there are four different color alleles:
– C is dominant over all of the others C = wild type color
– cch is dominant to ch and c
cch = chinchilla color
– ch is dominant to c
ch = Himalayan color
– c is recessive to everything
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?
 What is the probability
that they will have an
offspring that is
Himalayan?
 What is the probability
that they will have an
offspring that is albino?
 What is the probability
that they will have an
offspring that is wild
colored?
Parent one : Cch
Parent two : cc
50%
0%
50%
Cc
Cc
ch c
ch c
What is incomplete
dominance?
Practice incomplete
dominance:


Red Plant Genotype?
White Plant Genotype?
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?
 What is the phenotype
of the F1?
What is a polygenic
trait?
What is multifactorial
inheritance?
Summary:
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.
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.
Rr
ww
hybrid
pink
rw
rw
rw
rw
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.
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.