Transcript Slides

Topics for Today
• Review of Dihybrid Cross
- Relationship with molecular/chromosomal behavior
• Deductions from Pedigrees
• Calculation of Genetic Probabilities
Mendel’s Interpretations
Reinterpretted
Mendel’s Interpretation
Traits do not blend but are
determined by unchangeable
units
x
Our Interpretation
Genes
proteins
traits
Mendel’s Interpretations
Reinterpretted
Mendel’s Interpretation
Each trait is determined by
two units
Our Interpretation
Two
homologous
chromosomes
Mendel’s Interpretations
Reinterpretted
Mendel’s Interpretation
The two units may or may
not be identical
Our Interpretation
A
a
Genes come in different
forms, alleles, which make
different protein
Mendel’s Interpretations
Reinterpretted
Mendel’s Interpretation
One character form is
recessive to or dominant
over another
Our Interpretation
P >p
p >P
Mendel’s Interpretations
Reinterpretted
Mendel’s Interpretation
The two character forms
carried by a heterozygote are
passed to progeny with
equal likelihood
Law of Segregation
Our Interpretation
Mendel’s Interpretations
Reinterpretted
Mendel’s Interpretation
Different traits assort
independently
Law of Independent
Assortment
Our Interpretation
Different traits assort independently
Law of Independent Assortment
Different traits assort independently
Law of Independent Assortment
RRYY RRYy RrYY
RrYy
RRYy RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Deductions from Pedigrees
• Pedigree with ephemeral trait (Fig. 2)
• Pedigrees with other kinds of traits (next week)
• Genetic counseling (later today)
Deductions from Pedigrees
How is the trait inherited?
AA-?
A-
Try dominant
A-?
Deductions from Pedigrees
How is the trait inherited?
aa
aa
aa
aa
aa
aa
aa aa aa aa
aa
aa
aa
aa
aa A- aa A- aa
Any problem?
Deductions from Pedigrees
How is the trait inherited?
aa
aa
Try recessive
Deductions from Pedigrees
How is the trait inherited?
AA-
A-
AA-
A- A- A- A- A-
A-
A-
A- A-
A- aa A- aa ACan we get more?
Deductions from Pedigrees
How is the trait inherited?
Which one
gave a?
Which one
gave a?
AA-
A-
AA-
A- A- A- A- Aa
A-
A-
Aa A-
A- aa A- aa ACan we get more?
Deductions from Pedigrees
How is the trait inherited?
Which one
gave a?
Which one
gave a?
A-
What about
outsiders?
A-
Aa
AA-
A- A- A- A- Aa
Aa
A-
Aa A-
A- aa A- aa ACan we get more?
What about
outsiders?
Deductions from Pedigrees
How is the trait inherited?
AAA
Aa
AA-
A- A- A- A- Aa
Aa
AA
Aa AA
A- aa A- aa A-
Genetic Counseling
Make the
problem concrete
Will our children be normal ? ? ?
What’s the probability that a child of III.5 x III.6 will
will have
be aa?
CS?
Genetic Counseling
AAA
A-
aa
A-
A- A- A- A- A-
Parse the
problem
A-
AA
A-
A-
(start simple)
Child will be aa if:
III5 is Aa AND III6 is Aa AND III5
Probability:
a AND III6
a
Genetic Counseling
AAA
A-
aa
A-
A- A- A- A- A-
Solve each
segment
A-
AA
A-
A-
Child will be aa if:
III5 is Aa AND III6 is Aa AND III5
Probability:
II2 is Aa AND II2
1
a
1/2
1/2
a AND III6
a
1/2
Genetic Counseling
AAA
A-
aa
A-
A- A- A- A- A-
Solve each
segment
A-
AA
A-
A-
Child will be aa if:
III5 is Aa AND III6 is Aa AND III5
Probability:
1/2
1/2
1/2
a AND III6
a
1/2
Genetic Counseling
AAA
A-
aa
A-
A- A- A- A- A-
Put parts
together
A-
AA
A-
A-
Child will be aa if:
III5 is Aa AND III6 is Aa AND III5
Probability:
Multiply?
Add?
a AND III6
a
1/2
1/2
1/2
1/2
… intersection
union… mutually
… independent…
exclusive… fewer
more possibilities
possibilities
Union of possibilities
Probability that progeny of Aa x Aa has A phenotype
Male (Aa) makes
gamete
Gets A from female
OR
gets A from male
Female
(Aa)
makes
gamete
Rule of addition
union
mutually exclusive
A
a
A
AA
Aa
a
aA
aa
Gets aA OR AA OR Aa
P(A-) = 1/4 + 1/4 + 1/4 = 3/4
Intersection of possibilities
Probability that progeny of Aa x Aa has a phenotype
Male (Aa) makes
gamete
Gets a from female
AND
gets a from male
Female
(Aa)
makes
gamete
Rule of multiplication
intersection
independent
A
a
A
AA
Aa
a
aA
aa
Gets a from female AND gets a from male
P(aa) = 1/2
x
1/2 = 1/4
Genetic Counseling
AAA
A-
aa
A-
A- A- A- A- A-
Put parts
together
A-
AA
A-
A-
Child will be aa if:
III5 is Aa AND III6 is Aa AND III5
Probability:
Multiply?
Add?
a AND III6
a
x
x
x
1/2
1/2
1/2
1/2
… intersection
union… mutually
… independent…
exclusive…
1/16
fewer
more possibilities
possibilities
Example illustrating Rule of Complementation
• Suppose there are two genes (A, B) that are required for
dark hair
• A defect in any one of them will produce light hair
• What is the probability that a person will have light hair?
Make problem concrete:
Light hair if A- OR B-
Parse problem:
P(A- OR B-) = P(A-) + P(B-)
Is Rule of Addition valid here?
Is possession of A- and possession of B- mutually exclusive?
P(A
How to Calculate
OR
Probability of light hair
P(A-)
P(A-) + P(B-)?
B)
P(B-)
Not mutually exclusive.
P(A-B-) added twice
P(A
How to Calculate
OR
Probability of light hair
B)
P(A-) + P(B-)?
Not mutually exclusive.
P(A-B-) added twice
P(A-) x P(B-)?
Gives intersection, not union
P(A
How to Calculate
OR
Probability of light hair
P(A-)
P(B-)
P(A-): probability of possessing
defective allele of gene A
B)
P(A
How to Calculate
OR
Probability of light hair
not A-
P(not A-) = 1 - P(A-)
probability of not possessing
defective allele of gene A
B)
P(A
How to Calculate
OR
Probability of light hair
P(A-)
P(B-)
P(B-): probability of possessing
defective allele of gene B
B)
P(A
How to Calculate
OR
Probability of light hair
not B-
P(not B-) = 1 - P(B-)
probability of not possessing
defective allele of gene B
B)
P(A
How to Calculate
OR
Probability of light hair
not A-
P(not A-) = 1 - P(A-)
probability of not possessing
defective allele of gene A
B)
P(A
How to Calculate
OR
Probability of light hair
B)
not AAND
not B-
P(not A- and not B-) = [1 - P(A-)] x [1 - P(B-)]
probability of not possessing either defective
allele
P(A
How to Calculate
OR
Probability of light hair
B)
A- OR Bnot
A-
AND
not B-
P(A- or B-) = 1 - [1 - P(A-)] x [1 - P(B-)]
probability of possessing either defective allele
How likely to get hemophilia?
•There are five known alleles for the clotting factor protein
Factor VIII (H1-, H2-, H3-, H4-, H5-).
•Three of them (H3-, H4-, H5-) cause hemophilia.
H3-is the probability
hemophilia
•What
that a person will have one of the
H4-defective hemophilia
three
alleles and thus get hemophilia?
H5hemophilia
-, +H4-, OR H5-???
H4
P(H3
) = P(H3-) + P(H4-) + P(H5-)
Rule of addition
Union?
… but is possession of the alleles mutually exclusive?
Union of possibilities
Male (Aa) makes
gamete
A
a
P(A) = 0.5 P(a) = 0.5
Female
(Aa)
makes
gamete
A
P(A) = 0.8
AA
Aa
a
P(a) = 0.2
aA
aa
P(A-) = 0.4 + 0.4 + 0.1 = 0.9