AP Biology Discussion Notes
Wednesday 3/25/2015
Goals for the day
• Be able to predict the outcomes of crosses
with intermediate inheritance, co-dominance,
or multiple alleles
• Be able to define and perform dihybrid crosses
and use multiple strategies to predict the
outcomes
• Be able to use probabilities to simplify &
complete complex problems.
Question of the day 3/25
• Fill out the 3 questions at the top of your note
sheet -
Intermediate Inheritance & CoDominance
Answer the 3 questions at the top of your page.
Intermediate Inheritance & CoDominance
1. Based on the problems you have done
previously, predict the PHENOTYPE(s) of the
offspring from a cross between a Red flower and
a white flower where red is dominant to white.
Intermediate Inheritance & CoDominance
2. How many phenotypes were possible in the
problems we have done so far (look at the
legend or the phenotypic ratio)?
Intermediate Inheritance or
Incomplete Dominance
3. What does intermediate mean?
What does incomplete mean?
Intermediate Inheritance
Intermediate Inheritance/Incomplete Dominance - is
when two alleles BLEND together.
Example: When you cross a Red (FRFR) flower with a White
flower (FWFW) you get all pink flowers (FRFW) in the offspring.
(Red x White = 100% Pink)
Legend
Parents
Cross it
Genotypic Phenotypic
Ratio
Ratio
Intermediate Inheritance or
Incomplete Dominance
Note in the cross that the Genotype &
Phenotype ratios are now the same!
Co-Dominance
What does Dominance mean?
What does “CO” mean? (As in
cooperate or Coauthors)
Co-Dominance = Dominant together
Co-Dominance means: BOTH alleles are
represented that is they both SHOW UP!
(They are dominant together)
Intermediate inheritance & CoDominance
* The difference between Intermediate Inheritance & Codominance is in the PHENOTYPE.
In Intermediate Inheritance (aka Incomplete Dominance)
the alleles _________ together.
In Codominance both alleles _____ _______, are
EXPERESSED (Both traits are seen in the phenotype)
Cross a homozygous black dog with a
homozygous white dog
Legend
Parents
Cross it
Genotypic Phenotypic
Ratio
Ratio
Intermediate inheritance & CoDominance
Questions?
Multiple alleles
Some traits may be expressed by more than
two possible alleles. This is multiple allele
expression. One very important trait expressed
through multiple alleles is human blood type.
Multiple alleles
There are four possible types of human blood:
– A, B, AB, and O
•These are expressed by immunoglobulin
proteins, so the three possible alleles are written
in this way:
IA & IB are both CO-DOMINANT (they both
_______ ___) and i is recessive to them.
Multiple alleles
Multiple alleles – Traits are controlled by more
than 2 possible alleles.
Multiple alleles
Even with multiple alleles each individual still
only gets _______ alleles for each trait!
One allele from _______ and one allele from ______
Multiple alleles
Blood types in
Blood Type
Alleles
humans are a good
(________type) (_______type)
example of a
multiple allele trait.
AIA or IAi
I
- They are also an
example of
IBIB or IBi
CO-Dominance –
dominant together –
I A IB
Both alleles/traits
ii
_________ _____.
Multiple alleles
Very Important in Blood Transfusions!
Multiple alleles
Very Important in Blood Transfusions!
Multiple alleles
1. One parent is homozygous type A and the
other is heterozygous type A
Leg Parents
end
Cross it
Genotypic
Ratio
Phenotypic
Ratio
Mendel’s Law of Segregation
• Each individual has a pair of factors (alleles) for each
trait
• The alleles segregate (separate) during gamete
(sperm & egg) formation
• Each gamete contains only one factor (allele) for
each trait
• Fertilization gives the offspring two factors (alleles)
for each trait
Dihybrid Crosses
Up until now we have been looking at
Monohybrid crosses. Mono means _______.
This is to say that we have been looking at one
________, or characteristic, at a time. Often
times we want to look at two traits at once. If we
are looking at the outcomes of two traits in one
cross we will call it a __________ ___________.
•Di = _______
Mono = _________
Dihybrid Crosses
Often times we want to look at two traits at once.
If we are looking at the outcomes of two traits in
one cross we will call it a Dihybrid Cross
Di = _______
Mono = ______
Dihybrid Crosses
Dihybrid cross – two trait cross
In monohybrid crosses each parent was
represented with ___ alleles and there were ____
possible allele combinations.
(Ex. A parent could be AA, Aa, or aa)
Dihybrid Crosses
Dihybrid cross – two trait cross
In Dihybrid crosses there are ___ alleles/parent
and ____ possible Allele Combinations.
Mendel tested Two-Trait Inheritance
• Dihybrid cross Mendel used truebreeding (__________/____________)
plants differing in two traits
– Observed phenotypes among F2 plants
– Formulated Law of Independent Assortment
Mendel’s Law of Independent
Assortment
The Alleles for one trait segregate
(separate) independently of the alleles for
other traits
All possible combinations of alleles can occur in
the gametes(________/_______)
*These are ____________ cells ( __ n) and made
through the process of ____________
Meiosis Review
Let’s refresh our Memory! 
Organism
Cell type &
chromosome #
Mountain Goat
Horn cell = 50
Leopard Seal
Tongue cell = 10
Amaryllis Bulb
Egg cell = 15
Emperor Penguin Sperm cell = 20
Bald Eagle
Heart cell = 100
Haploid # Diploid #
Meiosis Review
Let’s refresh our Memory! 
Organism
Cell type &
chromosome #
Mountain Goat
Horn cell = 50
Leopard Seal
Tongue cell = 10
Amaryllis Bulb
Egg cell = 15
Emperor Penguin Sperm cell = 20
Bald Eagle
Heart cell = 100
Haploid # Diploid #
25
50
Meiosis Review
Let’s refresh our Memory! 
Organism
Cell type &
chromosome #
Mountain Goat
Horn cell = 50
Leopard Seal
Tongue cell = 10
Amaryllis Bulb
Egg cell = 15
Emperor Penguin Sperm cell = 20
Bald Eagle
Heart cell = 100
Haploid # Diploid #
25
5
50
10
Meiosis Review
Let’s refresh our Memory! 
Organism
Cell type &
chromosome #
Mountain Goat
Horn cell = 50
Leopard Seal
Tongue cell = 10
Amaryllis Bulb
Egg cell = 15
Emperor Penguin Sperm cell = 20
Bald Eagle
Heart cell = 100
Haploid # Diploid #
25
5
15
50
10
30
Meiosis Review
Let’s refresh our Memory! 
Organism
Cell type &
chromosome #
Mountain Goat
Horn cell = 50
Leopard Seal
Tongue cell = 10
Amaryllis Bulb
Egg cell = 15
Emperor Penguin Sperm cell = 20
Bald Eagle
Heart cell = 100
Haploid # Diploid #
25
5
15
50
10
30
20
40
Meiosis Review
Let’s refresh our Memory! 
Organism
Cell type &
chromosome #
Mountain Goat
Horn cell = 50
Leopard Seal
Tongue cell = 10
Amaryllis Bulb
Egg cell = 15
Emperor Penguin Sperm cell = 20
Bald Eagle
Heart cell = 100
Haploid # Diploid #
25
5
15
50
10
30
20
40
50
100
Mendel’s Law
of Independent Assortment
In honor of Mendel we will do an example of a
dihybrid cross with pea plants.
R – Round
Round is _______________ to wrinkled.
r – wrinkled
Y – Yellow
y - green
Yellow is ________________ to green.
Dihybrid Cross
Parental Generation (P1):
RRYY x rryy
Possible Gamete(s) from RRYY:
Possible Gamete(s) from rryy:
F1 gen. all (100%) RrYy
Dihybrid Cross – F.O.I.L
F1 generation: RrYy
F – first
O – Outside
I – Inside
L - Last
RrYy
Possible Gametes from RrYy:
______ , ______ , ______ , _______
R=Round r =wrinkled
Y= Yellow g= green
RY
RY
Ry
rY
ry
Ry
RrYy
rY
ry
R=Round r =wrinkled
Y= Yellow g= green
RY
rY
ry
RY RRYY RRYy
RrYY
RrYy
Ry RRYy
RRyy
RrYy
Rryy
rY RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
ry
Ry
RrYy
Phenotype (Phenotypic Ratio)
Round & Yellow: ___/16
Round & ________: ___/16
_________ & Yellow: ___/16
__________ & __________ : ___/16
Phenotype (Phenotypic Ratio)
Round & Yellow: ___/16
Round & ________: ___/16
_________ & Yellow: ___/16
__________ & __________ : ___/16
R=Round r =wrinkled
Y= Yellow g= green
RY
rY
ry
RY RRYY RRYy
RrYY
RrYy
Ry RRYy
RRyy
RrYy
Rryy
rY RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
ry
Ry
RrYy
Dihybrid Crosses
Phenotypic Ratio: ___: ___: ___: ___
- This will always be the phenotypic
ratio for a Heterozygote cross in normal
patterns of inheritance.
*This will also be a test question!
Typically for Dihybrid Crosses we will only ask you
to find the Phenotypic Ratio, and not the
Genotypic Ratios
Dihybrid Crosses REVIEW
There are now __ possible allele combinations
that could be passed on in the gametes of
these parents.
Remember that Crossing over, which happens
during Prophase 1 of Meiosis, is a source of
_______________.
*This Variation is in part why we might be
able to have __ different allele
combinations.
Dihybrid Crosses REVIEW
*This Variation is in part why we might be able to
have 4 different allele combinations.
If I had a heterozygote AaBb I might have AB
on one chromosome and ab on another. The
possible gametes then would only be AB and
ab. The ONLY WAY to get the other possible
gametes ___ ___ & ___ ___ are through
crossing over which allows the gametes to
inherit the alleles in a different way to have
(VARIATION)!!!
Wednesday PM
• I will be unavailable – talk to me if you plan to
work on corrections after school.
Species of the Day 3/25
Common Grackle
- Quiscalus quiscula
Species of the Day 3/25
Common Grackle
- Quiscalus quiscula
Species of the Day 3/25
Common Grackle
- Quiscalus quiscula
European Starling
- Sternus vulgaris