Transcript 3-11-11 canyousortitout2

3-11-11
IN
What are the probabilities of a monohybrid
cross between two heterozygous parents?
Flower color
R=red
r=white
3-11-11
Through
Quiz
Part B page 434
Notes
OUT
Bunny/Meiosis
worksheet
QUIZ!!!
Two Mendelian Traits: Pea
Pod color and Shape
Dihybrid cross -- A genetic cross
between individuals differing in two
alleles
In garden peas, the genes for the traits
of pod color and pod shape are on
different chromosomes.
Pod color
Green = G
Yellow = g
Pod shape
Expanded = E
Constricted= e
Peas that are homozygous for both
green and expanded are crossed with
peas that have yellow, constricted pods
Parent 1
Phenotype=Green, Expanded
Genotype= GGEE
Parent 2
Phenotype= Yellow, Constricted
Genotype= ggee
Through Meiosis, what are all the
possible gametes produced by the
parents?
Parent 1 G G E
E
GE
GE
GE
GE
Parent 2
ge
g
g
ge
e
ge
 To do a Dihybrid cross
1. Find possible gametes
2. Create a 4X4 table
3. Plug in gametes
4. Find offspring possibilities
e
ge
GE
Dihybrid cross
F1 Generation
GE
GE
GE
GgEe
GgEe
GgEe
GgEe
GgEe
GgEe
GgEe
GgEe
ge GgEe
GgEe
GgEe
GgEe
ge GgEe
GgEe
GgEe
GgEe
ge
ge
Results for possible offspring
for F1 generation
16 / 16 100%:
Phenotype- Green, Expanded
Genotype- GgEe
Carriers
To find a F2 generation, take two
offspring and cross them.
What are possible gametes for the F2
generation for each parent?
Parent 1---- GE, Ge, gE, ge
Parent 2---- GE, Ge, gE, ge
Complete the cross of the F2
Generation
GE
GE
Ge
gE
ge
Ge
gE
ge
GGEE GGEe
GgEE
GgEe
GGEe
GGee
GgEe
Ggee
GgEE
GgEe
ggEE
ggEe
GgEe
Ggee
ggEe
ggee
3. From the F2 generation, what fraction
would you predict to have each of the
following phenotypes?
A. The dominant phenotype for pod color
and pod shape.
9 / 16
B. The dominant phenotype for pod color
and recessive phenotype for pod shape.
3 / 16
C. The recessive phenotype for pod
color and the dominant phenotype for
pod shape.
3 / 16
D. The recessive phenotype for pod
color and pod shape.
1 / 16
4. If there were 288 offspring, how many
would you predict to be:
Green, Expanded?
162
Green, Constricted?
54
Yellow, Expanded?
54
Yellow, Constricted?
18
Actual Results
Green, expanded=165
Green, constricted= 51
Yellow, expanded=56
Yellow, constricted=16
A. Do the results match your
predictions?
B. Explain why they don’t match.
Short hair is a dominant trait for guinea pigs.
Both parents are heterozygous.
Complete a monohybrid cross for F1 generation.
What is the probability that their offspring will have
long hair?
S
s
S
SS
Ss
s
Ss
ss
Part C Linked-Traits
Many different genes are located on the
same chromosome.
When gametes are formed, alleles of
genes that are located on the same
chromosome end up together in the
same gamete.
Notes:
Linkage - genes that are on the same
chromosome end up together in the
same gamete.
1. Suppose the genes for pod color and
pod shape are on the same
chromosome.
G= green pod
g=yellow pod
E= Expanded pod e=constricted pod
Parent 1 GGEE
Gametes
GE/ GE/
Parent 2 ggee
Gametes
ge/
ge/
In this case, the green, expanded produce
only GE/ gametes and the yellow constricted
produce only ge/ gametes.
The slash represents the linkage
F1
GE/
ge/
ge/
GE/
GE/ge
GE/ge
GE/ge
GE/ge
Combine the gametes of two from the
F1 generation to find the F2 generation.
F2
GE/
GE/
ge/
ge/
GE/GE
GE/ge
GE/ge
ge/ge
Using linkage, what would be the
predicted phenotypes of the F2
generation?
75% green,expanded
25% yellow, constricted
Notes:
Crossing-over - During meiosis, it is
the breakage and exchange of
corresponding segments of
chromosome pairs.
Watch DVD “Crossing-over”
Describe the effect that crossing over
might have on results.
PART D X-Linked Traits
In fruit fly, Drosophilia melanogaster,
red eye color is dominant over white
eye color.
R-red
r-white
Predict the genotypes and phenotypes
you would expect in the F1 generation
when a homozygous red-eyed female
fly is mated with a white-eyed male fly.
Homozygous red-eyed female
RR genotype
White-eyed male
rr genotype
R
r
r
Predictions:
100% Rr genotype
100% Red-eyed offspring
R
Rr
Rr
Rr
Rr
2. Actual results
Based on 139 offspring, all had red eyes
3. Next, you mated a red-eyed male flies with
white-eyed female flies.(reciprocal cross)
Would you expect similar results?
4. In the early 1900’s, biologist Thomas Hunt
Morgan performed a similar cross. But,
instead of getting all red-eyed flies, he got
half red-eyed flies and half white-eyed flies.
However, all the red-eyed flies were females,
and all the white-eyed flies were males. How
might you explain these seemingly
unexpected results?
Read Need to know on page 436
5. A. A superscript letter designates
the allele. Often it is used with the
chromosome symbol to diagram a cross
of a trait that is carried on the X
chromosome. For example, the allele
for white eyes might be represented by
Xr, and the allele for red eyes by XR.
The symbol Y can represent the Y
chromosome and does not carry a
gene for eye color. Using these
symbols, diagram the cross described in
Step 3. Show the expected genotype
and phenotype fractions.
Male --- red-eyed
XRY
Female --- white-eyed
XrXr
Xr
XR
Y
Xr
XRXr
XRXr
Xr Y
XrY
Predictions:
Phenotypes 50% male 50% female
100% red-eyed female
100% white-eyed male
Diagram the cross that would result if
the F1 offspring were mated to create
the F2 generation. Show the genotypes
and phenotypes of the new offspring.
Male ---- XrY
Female ---- XRXr
Xr
Y
XR
XRXr
XRY
Xr
XrXr
XrY
Predicted outcomes:
Genotypes 25% XRXr, 25% XrXr,
25% XRY, 25% XrY
Phenotypes 50% females red-eyed,
50% females white-eyed,
50% males red-eyed, 50% males
white-eyed