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Bellwork: Fri. Jan. 8, 2016
In seals, the gene for the length of the whiskers is controlled by a
single gene. The dominant allele (W) codes long whiskers & the
recessive allele (w) codes for short whiskers.
If a homozygous dominate male seal and homozygous recessive
female seal mate, what is the probability that their pups will
have long whiskers?
Draw a Punnett Square indicate the cross:
______ X ______ and show the:
genotypic ratio:______:______
phenotypic ratio:_____:______
11–3 Exploring Mendelian Genetics
More on Genetics
Slide
3 of 31
End Show
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https://www.youtube.com/watch?v=-Vb-qGOJxlA
Copyright Pearson Prentice Hall
Probabilities Predict Averages
NOTES:
•Probabilities predict the average outcome of a large
number of events.
•Probability cannot predict the precise
outcome of an individual event!
•In genetics, the larger the number of offspring,
the closer the resulting numbers will get to
expected values.
Genotype
• Phenotype (Physical)
– Physical characteristics
• Genotype (Genetic)
– Genes we inherit from
our parents. “Gene”
make-up.
Phenotype
Notice the similarities:
– Eyes
– Smile
– Ears
– Nose
– Facial structure
– Neck
"No one ever believes
we are twins because
I am white and Maria
is black,"
- Lucy
NOTES
law of segregation: when gametes are
made, each member of allele pair separates
from the other member to form the genetic
make-up of the gamete
(monohybrid cross: )
Independent Assortment: To determine if the
segregation of one pair of alleles affects the
segregation of another pair of alleles in a twofactor cross.
(dihybrid cross)
The Test Cross
What if you want to figure out an unknown
genotype of an organism with a dominant
phenotype?
For example, what if you have a rabbit with
black hair and want to know if it is homozygous
dominant or heterozygous?
• Mendel realized that it is possible to
find the genotype of an organism
simply by crossing. This does not
require modern technology.
Test Cross: crossing an organism with an
unknown genotype and dominant
phenotype with a homozygous recessive
organism to determine the unknown
genotype.
Is it YY or Yy? (both “appear” yellow)
Phenotype
To identify the genotype of yellowseeded pea plants as either homozygous
dominant (YY) or heterozygous (Yy), you
could do a test cross with plants of
genotype _______.
If the unknown genotype is
homozygous dominant (YY)…
The offspring will ALL have a yellow phenotype.
If the unknown genotype is
heterozygous (Yy)…
Half of the offspring will be yellow and half will be
green.
So if we take our black rabbit (unknown genotype)
and cross it with a brown rabbit (homozygous
recessive genotype) we get:
b
b
B
Bb
Bb
?
?b
?b
B? x bb
If the unknown genotype is homozygous dominant, what results
would you expect from the offspring?
So if we take our black rabbit (unknown genotype)
and cross it with a brown rabbit (homozygous
recessive genotype) we get:
BB x bb
b
b
B
Bb
Bb
B
Bb
Bb
ALL of the offspring will be black.
So if we take our black rabbit (unknown genotype)
and cross it with a brown rabbit (homozygous
recessive genotype) we get:
b
b
B
Bb
Bb
?
?b
?b
B? x bb
If the unknown genotype is heterozygous, what results would
you expect from the offspring?
Example only not in notes 2013
• In fruit flies, the allele W for long wings is dominant
over the allele w for short wings.
• Calculate the probability of heterozygous offspring
resulting from a cross between two homozygous
recessive parents.
Cross: ____ x _____
(looking for Ww “baby” flies)
Genotypic ratio:
Phenotypic ratio:
Probability:
All ww  4:0
All short-winged: 4:0
P(Ww) = 0 Ww = 0 = 0%
• In fruit flies, the allele W for long wings is dominant
over the allele w for short wings.
• Calculate the probability of long-winged offspring
resulting from a cross between a heterozygous parent
and a homozygous recessive parent.
Cross: _____ x ______
2 Ww and 2 ww, so 0:2:2
2 long-winged and 2 short-winged, so 2:2
P(WW or Ww)= 2/4 = 0.5 = 50%
Genotypic ratio:
Phenotypic ratio:
Probability:
The Dihybrid Cross: cross involving two
sets of traits (alleles) – a monohybrid
cross involves one set of traits (alleles)
Genotypic Ratio:
Phenotypic Ratio:
Genotypic Ratio:
RRYY:
RRYy:
RRyy:
RrYY:
RrYy:
Rryy:
rrYY:
rrYy:
Rryy:
1:1:2:2:4:2:2:1:1
Phenotypic Ratio:
Round Yellow
Round Green
Wrinkled Yellow
Wrinkle Green
9:3:3:1
A Summary of Mendel's Principles
• Genes are passed from parents to offspring.
• There are dominant and recessive alleles.
• Allele pairs from each parent separate in gamete formation:
law of segregation.
•
Genes for different traits (on different chromosomes) can
segregate independently during the formation of gametes:
independent assortment.
• Genes that segregate independently do not influence each
other's inheritance.
•
alleles for different genes usually segregate independently of
one another unless they are on the same chromosome
Mendel didn’t know about Chromosomes or
DNA
We now know that genes located close together
on a chromosome may be inherited together
http://www.google.com/imgres?imgurl=http://www.schenectady.k12.ny.us/putman/biology/data/images/inheritance/5vtxrn.gif&imgrefurl=http://www.schenectad
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Copyright Pearson Prentice Hall
• https://www.youtube.com/watch?v=G3LLt
ZUdpvA&list=PLD2bkg3sRPUOjPf9Du8tS
48vhan5dNi0L&index=89
END
Copyright Pearson Prentice Hall
But… some alleles aren’t completely
dominate or recessive
Bellwork: Tues. Jan 13, 2015
Short hair is dominant
long hair is recessive
Show a cross between two heterozygous guinea pigs. What
% of the offspring will have short hair? ________
What %of the offspring will have long hair? _______
Two short haired guinea pigs are mated several times. Out
of 100 offspring, 25 of them have long hair. What are the
probable genotypes of the parents?
• ________ x ___________
Incomplete &
Codominance
Incomplete Dominance: when one allele is not
completely dominant over another. The
heterozygous phenotype is a “mix of the two
homozygous phenotypes.
A cross between red (RR)
and white (WW) four o’clock
plants produces pink-colored
flowers (RW).
Incomplete dominance – when one allele is
not completely dominant over the other allele
WW = White
RR = Red
RW = Pink
•Genotypic Ratio:__________
•Phenotypic Ratio:_________
WW X RR
• What happens if you cross the offspring
(F1) generation?
RW x RW
• Genotypic ratio
• Phenotypic Ratio
Codominance
Is a lot like incomplete dominance - A
hybrid organism shows a third
phenotype --- not the usual dominant
versus recessive traits. BUT in
codominance both traits show up AT
THE SAME TIME!!
Co-dominance: when both alleles contribute to
the phenotype.
•A cross of black chicken (BB) with a white
chicken (WW) produces all speckled offspring
(BW).
BB = black feathers
BW = black and white feathers
WW = white feathers
Genotypic Ratio:
Phenotypic Ratio:
• Or…. Roan coat color in horses and
cows.
Co-dominance: Roan fur. Cattle can be
ored (RR = all red hairs),
owhite (rr = all white hairs), or
oroan (Rr = red & white hairs together).
Notice how this cross looks just like the others we
have done earlier with dominant and recessive
alleles – I would have to tell you this is a codominant cross!!!.
Cross: ______ X _______
Genotypic Ratio:_____________
Phenotypic Ratio:____________
Now let’s cross two roans:
Cross:_____ X______
Genotypic Ratio:
Phenotypic Ratio:
roan horses
• https://www.youtube.com/watch?v=YJHG
fbW55l0
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Bellwork: Thurs. Jan. 13, 2011
Dihybrid: 2-Factor Cross: First Generation: F1
Mendel crossed true-breeding plants that produced round
yellow peas (genotype RRYY) with true-breeding plants that
produced wrinkled green peas (genotype rryy):
(R) = Round seeds (r) = wrinkled seeds
(Y) = Yellow seeds (y) = green seeds
Cross: RRYY
x
rryy
Genotypic Ratio: ______________
Phenotypic Ratio: ______________
The Punnett square predicts a
Genotypic Ratio:
1:1:2:2:4:2:2:1:1
Phenotypic Ratio:
9:3:3:1
F2 Represents:
Independent Assortment
Bellwork: Thurs. Jan. 8, 2015
Cross a female with blonde hair to a male with
Brown Hair (B)
heterozygous brown hair:
YES!!! Write all of the Blonde Hair (b)
RED words &
1st, write the cross:
punnett square!!!!!!
________ x ________
Genotypic ratio:_____________
Phenotypic ratio:_____________
What % will have blonde hair?______
What % will have brown hair?______
What fraction will have brown hair?___
What fraction will have blonde hair? ___
Bellwork: Mon???. Jan. 20??, 201?
Dihybrid: 2-Factor Cross: First Generation: F1
Mendel crossed true-breeding plants that produced round
yellow peas (genotype RRYY) with true-breeding plants that
produced wrinkled green peas (genotype rryy):
(R) = Round seeds (r) = wrinkled seeds
(Y) = Yellow seeds (y) = green seeds
Cross: RRYY
x
rryy
Genotypic Ratio: ______________
Phenotypic Ratio: ______________
Bellwork: Mon. Jan. 9, 2012
Mendel crossed true-breeding plants that produced round
yellow peas (genotype RRYY) with true-breeding plants that
produced wrinkled green peas (genotype rryy):
Set up the Punnet Square for this cross:
RRYY x rryy