ZOL 141 1nd Edition Lecture 16 Outline of Last Lecture I X linked dominant traits A Ex XLH II X linked recessive traits a Duchenne muscular dystrophy III Y linked traits IV Mitochondrial traits V Three parent baby Outline of Current Lecture VI Determining patterns of inheritance VII Predicting genetic risk using pedigrees a example VIII complications to pedigree analysis Current Lecture Determining Pattern of Inheritance Mitochondrial o Offspring must have same status as mother mother unaffected all children must be unaffected vice versa Y linked o No females affected o Sons must have same status as father X linked dominant o Often more females affected than males o Affected males must transmit trait to all daughters o Affected males must have affected mothers o Affected females must have affected parents X linked recessive o More males should be affected than females o Affected females must have affected sons o Affected females must have affected fathers Autosomal dominant o Trait expressed in males and females in roughly equal proportions o Affected individuals must have at least one affected parent o Offspring of affected parents can be unaffected Autosomal recessive o Trait expressed in males and females in roughly equal proportions o Unaffected parents may have affected child o Offspring of two affected parents must be affected Predicting genetic risk using pedigrees An unaffected married couple is currently expecting their first child They visit a genetic counselor wanting to know about the likelihood that their child will be affected by cystic fibrosis autosomal recessive disease Probability their child will be affected o Neither parent is affected o Rr x RR o 0 chance Rr x Rr o 25 chance R x Rr o Look at parents pedigrees o Set up punnett square for dad s parents o 2 3 chance because rr not possible o 2 3 x 1 x 1 6 R x R o Punnett squares for both grandparents o 2 3 x x 1 12 Complications to pedigree analysis Heteroplasmy o Situation in which within a single cell there is a mixture of mitochondria some containing mutant DNA and some containing normal DNA o Variable expressivity based on numbers of mutant mitochondria Conditions that manifest late in life o Individuals may not be symptomatic at the time the pedigree is constructed o Individuals may pass away from unrelated causes before they are symptomatic o Ex Huntington s disease Symptoms Usually appear midadulthood Behavioral or emotional problems uncontrolled or involuntary movements and dementia Causes Mutations in HTT gene that leads to production of an abnormall long version of the Huntington protein CAG trinucleotide repeat 10 35 normal 35 39 possible huntington s 40 60 adult onset 60 juvenile onset Polyglutamine expansion makes protein toxic kills cells in brain and nervous system Treatment none