Lec 7 Bio 308
Lec 7 Bio 308 Bio 308
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This 6 page Class Notes was uploaded by Kiara Reyes on Monday September 19, 2016. The Class Notes belongs to Bio 308 at Northern Illinois University taught by M. Johns in Summer 2016. Since its upload, it has received 4 views. For similar materials see Genetics in Biology at Northern Illinois University.
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Date Created: 09/19/16
Lecture 7: Pedigree Analysis “Goals of Pedigree Analysis” 1. Determine the mode of inheritance: dominance, recessive, partial dominance, sex-linked, autosomal, mitochondrial, and maternal effect 2. Determine the probability of an affected offspring for a given cross Y-linked Inheritance Traits on the Y chromosome are only found in males, never in females The fathers traits are passed to all sons Dominance is irrelevant: there is only 1 copy of each Y-linked gene (hemizygous) Mitochondrial Genes Mitochondrial are only inherited from the mother Females that have mitochondrial traits= her offspring inherit Males that have mitochondrial traits= none of his offsprings inherit it Note: only 1 allele is present in each individual, so dominance isn’t an issue Outsider Rules In pedigree there are people whose parents are unknown called “outsiders” Outsiders Rule Dominants Pedigree: affected outside are assumed to be heterozygotes Outsiders Rule Recessive Pedigree: unaffected (normal) outsiders are assumed to be homozygotes Both of these rules are derived from the observation that mutant alleles are rare Maternal Effect Genes “Mothers genotype determines offsprings phenotype” Assume that the traits is recessive in a complete dominance situation Also assume all outsiders are homozygous for the allele they are expressing: the dominant allele is they are unaffected and the recessive allele if they are affected Sex-Influenced Traits Assume that the traits is dominant in male but recessive in females Assume all outsiders are homozygous: -DD is always affected -dd is always normal -Dd is affected in males but normal in females Sex-Limited Traits Several possibilities for dominance, but for this problem assume the traits is dominant but only expressed in males Affected outsiders males are heterozygous; unaffected males are homozygous normal Assume that outsider females are homozygous normal Sex-Linked Dominant Mother’s pass their X’s to both son’s and daughter’s Father passes their X to daughters only Normal outsider rule for dominant pedigree for females, but for sex- linked traits remember that males are hemizygous and express which ever gene is on their X Sex-Linked Recessive All affected are homozygotes Unaffected outsiders are assumed to be homozygous normal Consanguineous mattings are often (but not always) involved Autosomal Dominant Assume affected outsiders are assume to be heterozygous All unaffected individuals are homozygous for the normal recessive allele Autosomal Recessive All affected are homozygotes Unaffected outsiders are assumed to be homozygous normal Consanguineous matings are often (but not always) involved Large Pedigrees Analysis of Dominant and Recessive autosomal pedigree Main Problems: 1. Determine inheritance type 2. Determine genotype for various individuals 3. Determine the probability of an affected offspring between two members of the chart Dominant vs Recessive 1. If two affected people have an unaffected child, it must be a dominant pedigree 2. If two unaffected people have an affected child, it is a recessive pedigree 3. If every affected person has an affected parent, it is a Dominant Pedigree “Dominance Autosomal Pedigree” 1. All unaffected are dd 2. Affected children of an affected parent and unaffected parent must be heterozygous Dd, because they inherited “d” allele from unaffected parent 3. Affected parents of an unaffected child must be heterozygous Dd, since they both passed “d” allele to their child 4. Outsider Rule for dominant autosomal pedigree: An affected outsider (person with no known parents) is assumed to be heterozygous Dd 5. If both parents are heterozygous Dd x Dd, their affected offspring have a 2/3 chance of being DD and 1/3 chance being DD “Recessive Autosomal Pedigree” 1. All affected are rr 2. If an affected person (rr) mates with an unaffected person, any unaffected offspring must be Rr heterozygous, because they got a “r” allele from their affected parent 3. If two unaffected mate and have an affected child, both parents must be Rr heterozygous 4. Recessive outsider rule: Outsiders are those whose parents are unknown. In a recessive autosomal pedigree, unaffected outsiders are assumed to be RR homozygous normal 5. Unaffected RR x Rr have a ½ chance and ½ chance Rr 6. Unaffected children Rr x Rr have 2/3 chance being Rr and 1/3 chance being RR
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