Genetics

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Genetics
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Mendelian Genetics
While assigned to teach, he was also assigned to
tend the gardens and grow vegetables for the
monks to eat.
Augustinian Monk at Brno Monastery in Austria
(now Czech Republic)
Not a great teacher but well trained in math,
statistics, probability, physics, and interested
in plants and heredity.
Mountains with short, cool growing season meant
pea (Pisum sativum) was an ideal crop plant.

• Gregor Mendel
• Father of Genetics

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Gregor Mendels Work

• Starting in 1856 Mendel studied peas which he
  grew in a garden out side the Abbey he lived in.
• Showed that the traits he studied behaved in a
  precise mathematical way and disproved the theory
  of "blended inheritance.
• Mendels work was rediscovered in 1900 by three
  botanists
• Carl Correns (Germany)
• Erich von Tschermak (Austria)
• Hugo de Vries (Holland)

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Why Peas?

• Mendel used peas to study inheritance because
• True breeding commercial strains were available
• Peas are easy to grow
• Peas have many easy to observe traits including

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Consistency is Good
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Gene Expression

• Each form of the particular gene is an allele.
• Alleles can be either
• Dominant always show trait - T
• Recessive only see if dominant trait absent t
• In order to see the trait expressed, 2 alleles
  must be paired together (one from mom and one
  from dad)

T
Tt
t

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Gene Expression

• Genes come in pairs that separate during the
  formation of gametes (meiosis).
• The members of these pairs can be the same
  (homozygous) or different (heterozygous).

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PracticeTake out the Applying Genetics
Terminology paper and complete.You have 2
minutes.
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Gene Expression

• When two alleles are paired we can express them
  by their phenotype or genotype.
• Phenotype physical characteristics
• Ex. Tall, Short, Dark, Round, Wrinkled
• Genotype the allele combination or genes
• Ex. AA, Aa, aa, Dd, Rr, rr, tt

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Using terminology
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Results of Mendels monohybrid parental
cross Mendels Principle of Dominance F1
offspring of a monohybrid cross of true-breeding
strains resemble only one of the
parents. Why? Smooth seeds
(allele S) are completely dominant to wrinkled
seeds (allele s).
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Example of Mendels Work
Smooth
Wrinkled
x
Phenotype
P
SS
ss
Genotype
Homozygous Dominant
Homozygous Recessive
All Smooth
Clearly Smooth is Inherited What happened to
wrinkled?
F1
Ss

1. Smooth is dominant to wrinkled
2. Use S/s rather than W/w for symbolic logic

Heterozygous
F1 x F1 F2
possible gametes
NEVER use S/W or s/w
Punnett Square
s
S
3/4 Smooth 1/4 wrinkled
F2
Smooth Ss
Smooth SS
S
possible gametes
wrinkled ss
Smooth Ss
s
wrinkled is not missingjust masked as
recessive in diploid state
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Mendel as a Scientist
Test Cross
Unknown Smooth
Wrinkled
x
ss
possible gametes
If Unknown is SS
s
s
Smooth Ss
Smooth Ss
S
possible gametes
Test Progeny All Smooth
Smooth Ss
Smooth Ss
S
possible gametes
If Unknown is Ss
s
s
S
Smooth Ss
Smooth Ss
possible gametes
Test Progeny Half Smooth Half wrinkled
Wrinkled ss
Wrinkled ss
s
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• Mendels Principle of Segregation
• Recessive characters masked in the F1 progeny of
  two true-breeding strains, reappear in a specific
  proportion of the F2 progeny.
• Two members of a gene pair segregate (separate)
  from each other during the formation of gametes.

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Monohybrid Crosses Yielded Consistent Results
Therefore, the Principle of Segregation indeed is
a general principle of genetics.
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Probability and Genetics
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Equation for probability

• NUMBER OF THINGS YOU ARE LOOKING
  FOR
• PROBABILITY -----------------------------------
  
  TOTAL NUMBER OF THINGS

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I have quarter in my pocket. What is the
probability that I get heads when flipped?
Answer ½
You have a total of 2 sides and 1 of them is
heads.
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I have 3 pennies and 5 nickels in my pocket. If
I pull out one coin what is the probability that
I get a nickel?
Answer 5/8
You have a total of 8 coins and 5 of them are
nickels.
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Chi-Square Analysis determine how close your
data is to the known probability of occurrence
50 each
If I tossed a coin 100 times, how many heads
would you expect to get? Tails?
What if you didnt get 50 50?
How would you know if the numbers you got were
good enough?
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Chi-SquareLets look at the chance of flipping
heads or tails



o e (d)
d2/e
Options
Observed (o)
Expected (e)
d2
43-50 -7
49/50 .98
72 49
Heads
43
50
57-50 7
72 49
49/50 .98
Tails
57
50
X2 1.96
N (degree of freedom) of options 1
N 2 - 1
Add this column for X2
N 1
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Chi-Square cont. What do I do with these
numbers?
N 1 X2 1.96
Once the Chi-square and N values are computed,
look on the chart.
Degrees of Freedom Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P) Probability Values (P)
(N) .95 .90 .80 .70 .50 .30 .20 .10 .05 .01
1 .004 .016 .064 .148 .455 1.07 1.64 2.71 3.84 6.64
2 .103 .211 .446 .713 1.39 2.41 3.22 4.61 5.99 9.21
3 .352 .584 1.00 1.42 2.37 3.66 4.64 6.25 7.82 11.34
X2 values are in the shaded region
N value look here
P about 17
If the probability (P) given in the table is
high, it is very likely that this would occur by
chance, and we have a good fit. If P is low,
we conclude that it is not likely that the
deviation observed would occur by chance alone.
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Activity Probability and Chi-Squares
With a partner, get 2 pennies ( or any coin).
Toss your coins 100 times. Make sure you record
on the chart how many HH, HT and TT you
got. Using Chi-Square analysis, how fit was your
data?
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(No Transcript)
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What is the probability of each landing on heads
or tails?
Heads 1/2
Tails 1/2
Punnett Squares work in the same manner


HH 1/4
HT 1/4
Heads 1/2
TT 1/4
HT 1/4
Tails 1/2
Phenotype
1/4 Heads/Heads
1/2 Heads/Tails
1/4 Tails/Tails
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Alleles T tall t short
Tt
What are the possible gametes produced by these
parents?
T
t


Phenotype
Tall
Tall
T
¾ or 75 Tall
TT
Tt
½ or 25 short
Tt
Tall
Short
t
Genotype
Tt
tt
¼ or 25 TT
2/4 or 50 Tt
¼ or 25 tt
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Practicing Monohybrid Punnett Squares

• Exercise Punnett Squares
• Do numbers 1, 2 and 3 make sure to include
  phenotype and genotype ratios
• Get each problem checked by me before you move to
  the next

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With a partner, go to the back of the room and
complete the lab. You will need your chi-square
chart.
Lab Corn Genetics