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## Topics for Today

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**Topics for Today**• Review of Dihybrid Cross- Relationship with molecular/chromosomal behavior • Deductions from Pedigrees • Calculation of Genetic Probabilities**Mendel’s InterpretationsReinterpretted**Mendel’s Interpretation Our Interpretation Traits do not blend but are determined by unchangeable units Genes proteins traits x**Mendel’s InterpretationsReinterpretted**Mendel’s Interpretation Our Interpretation Each trait is determined by two units Two homologous chromosomes**Mendel’s InterpretationsReinterpretted**Mendel’s Interpretation Our Interpretation A a The two units may or may not be identical Genes come in different forms, alleles, which make different protein**Mendel’s InterpretationsReinterpretted**Mendel’s Interpretation Our Interpretation One character form is recessive to or dominant over another P > p p > P**Mendel’s InterpretationsReinterpretted**Mendel’s Interpretation Our Interpretation The two character forms carried by a heterozygote are passed to progeny with equal likelihood Law of Segregation**Mendel’s InterpretationsReinterpretted**Mendel’s Interpretation Our Interpretation Different traits assort independently Law of Independent Assortment**Different traits assort independentlyLaw of Independent**Assortment**Different traits assort independentlyLaw of Independent**Assortment**Deductions from Pedigrees**• Pedigree with ephemeral trait (Fig. 2) • Pedigrees with other kinds of traits (next week) • Genetic counseling (later today)**Deductions from PedigreesHow is the trait inherited?**A- A- A-? A-? Try dominant**Deductions from PedigreesHow is the trait inherited?**aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa A- aa A- aa Any problem?**Deductions from PedigreesHow is the trait inherited?**aa aa Try recessive**Deductions from PedigreesHow is the trait inherited?**A- A- A- A- A- A- A- A- A- A- A- A- A- A- A- A- A- aa A- aa A- Can we get more?**Deductions from PedigreesHow is the trait inherited?**Which one gave a? Which one gave a? A- A- A- A- A- A- A- A- A- A- A- A- A- A- A- Aa Aa A- A- aa A- aa A- Can we get more?**Deductions from PedigreesHow is the trait inherited?**Which one gave a? Which one gave a? A- A- What about outsiders? What about outsiders? A- Aa A- Aa A- A- A- A- A- Aa Aa A- A- aa A- aa A- Can we get more?**Deductions from PedigreesHow is the trait inherited?**A- A- AA Aa A- Aa AA A- A- A- A- Aa AaAA 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 have CS? What’s the probability that a child of III.5 x III.6 will be aa?**Genetic Counseling**A- aa Parse the problem (start simple) AA A- A- A- AA A- A- A- A- A- A- A- Child will be aa if: AND III5a AND III6a III5 is Aa AND III6 is Aa Probability:**Genetic Counseling**A- aa Solve each segment AA A- A- A- AA A- A- A- A- A- A- A- Child will be aa if: AND III5a AND III6a III5 is Aa AND III6 is Aa Probability: II2 is Aa AND II2a 1/2 1/2 1 1/2**Genetic Counseling**A- aa Solve each segment AA A- A- A- AA A- A- A- A- A- A- A- Child will be aa if: AND III5a AND III6a III5 is Aa AND III6 is Aa Probability: 1/2 1/2 1/2 1/2**Genetic Counseling**A- aa Put partstogether AA A- A- A- AA A- A- A- A- A- A- A- Child will be aa if: AND III5a AND III6a III5 is Aa AND III6 is Aa Probability: 1/2 1/2 1/2 1/2 Multiply? Add? … union… mutually exclusive… more possibilities … intersection … independent… fewer possibilities**Union of possibilities**Probability that progeny of Aa x Aa has A phenotype Gets A from female OR gets A from male Rule of additionunionmutually exclusive 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 Gets a from female AND gets a from male Rule of multiplicationintersectionindependent Gets a from female AND gets a from male P(aa) = 1/2 x 1/2 = 1/4**Genetic Counseling**A- aa Put partstogether AA A- A- A- AA A- A- A- A- A- A- A- Child will be aa if: AND III5a AND III6a III5 is Aa AND III6 is Aa x x x Probability: 1/2 1/2 1/2 1/2 Multiply? Add? … intersection … independent… fewer possibilities … union… mutually exclusive… more possibilities 1/16**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?**How to Calculate P(A- OR B-)Probability of light hair**P(A-) P(B-) P(A-) + P(B-)? Not mutually exclusive.P(A-B-) added twice**How to Calculate P(A- OR B-)Probability of light hair**P(A-) + P(B-)? Not mutually exclusive.P(A-B-) added twice P(A-) x P(B-)? Gives intersection, not union**How to Calculate P(A- OR B-)Probability of light hair**P(A-) P(B-) P(A-): probability of possessing defective allele of gene A**How to Calculate P(A- OR B-)Probability of light hair**not A- P(not A-) = 1 - P(A-) probability of not possessing defective allele of gene A**How to Calculate P(A- OR B-)Probability of light hair**P(A-) P(B-) P(B-): probability of possessing defective allele of gene B**How to Calculate P(A- OR B-)Probability of light hair**not B- P(not B-) = 1 - P(B-) probability of not possessing defective allele of gene B**How to Calculate P(A- OR B-)Probability of light hair**not A- P(not A-) = 1 - P(A-) probability of not possessing defective allele of gene A**How to Calculate P(A- OR B-)Probability of light hair**not A-ANDnot B- P(not A- and not B-) = [1 - P(A-)] x [1 - P(B-)] probability of not possessing either defective allele**How to Calculate P(A- OR B-)Probability of light hair**A-OR B- not A-ANDnot 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- hemophilia H4- hemophilia H5- hemophilia H4+ ??? • What is the probability that a person will have one of the three defective alleles and thus get hemophilia? P(H3-, H4-, OR H5-) = P(H3-) + P(H4-) + P(H5-) Rule of addition Union? … but is possession of the alleles mutually exclusive?**Union of possibilities**P(A-) = 0.4 + 0.4 + 0.1 = 0.9