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Fnord babies Do Now, 2/19
Objective: Define incomplete dominance and
codominance, and solve genetics problems involving both.
Task:
In Fnords, orange (O) skin is dominant over blue skin (o). An
orange fnord and a blue fnord mate, and produce 314 orange
offspring and 307 blue offspring.
A. What is the genotype of the orange parent?
B. Two orange fnords mate, and they produce both orange and
blue offspring. If they have 98 blue babies, about how many
orange ones are there?
C. Describe a cross you could make to figure out if an orange
fnord is homozygous dominant or heterozygous.
FNORDS!
O
o
O
OO
Oo
o
Oo
oo
A. Oo
B. about 300
C. cross with a blue
fnord. If all
offspring are
orange, must
have been a
homozygote.
Testcross
Important Info from 9.1-9.2
• Generation titles
P generation =
parents
F1 generation =
offspring generation
1 (Latin filial = son)
F2 generation =
offspring generation
2 (from F1 self
fertilization)
Beyond Complete Dominance
• In the crosses we looked at earlier, one
allele (form of a gene) was completely
dominant over the other.
• Ex. Tt = phenotype “T”
• Example Problems (2) on Back of Notes
• Some traits are more complex however…
Codominance
For a trait that is codominant,
heterozygotes display BOTH
phenotypes.
Look at the example of horses
RR = Red fur
rr = White fur
Rr = Red AND White fur (roan)
Codominance Example – Roan
Horses
Codominance = Both
• In Camellia flowers, for example…
Genotype
Phenotype
PP
Pink
Pp
Pink & White
pp
white
Incomplete Dominance
The heterozygote genotype has a blend of both possible
homozygous phenotypes.
RR
Rr
rr
Pink flowers = RR’
• Since one allele isn’t really dominant, the
non-functional allele (white in this
example) is written with a capital letter and
an apostrophe (i.e. R’, Q’, etc.) and called
“R prime” for example.
Flower Power
• If you crossed two of the pink flowers on
the previous slide,
– What % would be pink?
– What % would be red?
– What % would be white?
• What is the phenotype ratio?
Recap: Codominance & Incomplete
Dominance
Codominance
Incomplete
Dominance
Heterozygotes get
BOTH phenotypes
Heterozygotes
get a BLEND of
phenotypes
Note: The 2-point problems in the
genetics problem set are examples
of these.
Exit Ticket
• On a seperate sheet of paper:
– Problems on back of notes
• Incomplete Dominance example #1
• Codominance example #1
– Include a Punnett square
Do Now 2.11
OBJECTIVES:
1. Complete objectives from yesterday
2. Define, identify, and use Punnett squares to analyze genetic
crosses for traits that are codominant and incompletely
dominant.
TASK:
1. In Flibs, sex is determined by X and Y chromosomes just as it
is in humans. Having feathers is a phenotype produced by a
recessive allele on the X chromosome.
A. What is the genotype of a male with feathers?
B. What are the two possible genotypes of a female with no
feathers?
C. If a feathered female is crossed with a featherless male, what
% of the female offspring will have feathers?
Do Now 3.1
• Objective:
– 1. Define sex-linkage, and describe how sex-linked
traits are inherited.
• Task:
– 1. In unicorns, having a horn (H) is dominant to not
having a horn (h). A unicorn with a horn is bred
with a hornless unicorn.
• What is the expected phenotype ratio of the offspring if
the horned parent is homozygous?
• If it is heterozygous?
Shh!
Don’t say
a word!
Write
down what
numbers (if
any) you
can read in
each circle
Are you color blind?
• 4 Sex-Linked Traits:
• 1. Normal Color Vision:
A: 29, B: 45, C: --, D: 26
• 2. Red-Green Color-Blind:
A: 70, B: --, C: 5, D: -• 3. Red Color-blind:
A: 70, B: --, C: 5, D: 6
• 4. Green Color-Blind:
A: 70, B: --, C: 5, D: 2
Sex-Linkage: Crucial Information
• In humans, almost all
sex-linked genes are
on the X chromosome
• Sex-linked recessive
phenotypes are FAR
more common in
males
• Males only have 1
copy of X-linked
genes.
There are a LOT more color blind
men than women!
Boys and
Girls are
Different
• Sex-linked
genes cause a
phenotype ratio
difference
between males
and females.
Try One – as sex-linkage example
in notes
• A female with normal vision that has 1 copy of a
colorblindness gene (genotype X+ Xo) has
children with a normal male (X+ Y).
A. What % of their male children will be
colorblind?
B. What % of their female children will be
colorblind?
C. Do all colorblind women have a colorblind
father? Explain
Recap: Sex-linkage
• In humans, almost all sex-liked genes are
carried on the X-chromosome, and are
recessive.
• Recessive X-linked phenotypes are
MUCH more common in MALES.
3 Different Alleles: Multiple Allele
Traits
• The three alleles that determine blood type
are represented as IA, IB, and i.
Phenotype
Genotypes
A
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
Crosses
• A woman with blood type A has a baby with
blood type O. The man she believes to be
the father has the blood type AB. Is it
possible the man is the father of the baby?
He isn’t the Father!
Possible
dad
mom
IA
IB
IA
IAIA
(A)
IAIB
(AB)
i
IAi
(A)
IBi
(B)
Multiple Allelic Traits
• Traits for which there are 3 or more alleles
are said to be multiple allele traits, or
multiple allelic.
• Try the example cross on your notes
Wrap up
• Alleles can react in different ways, for
different genes:
– Codominance: both alleles expressed (roan
horses)
– Incomplete: heterozygote has blended
phenotype (pink flowers)
– Sex-linkage: males only get 1 copy!
(colorblindness)
– Multiple alleles: 3 or more alleles for 1 gene.
(blood type)
Homework
• Syllabus reading
• You should now be able to work on the
1,2, and 3-point problems on the
“Classical Genetics Problem Set.”