ZOL 141 1nd Edition Lecture 16 Outline of Last Lecture I. X-linked dominant traitsA. Ex: XLHII. X-linked recessive traitsa. Duchenne muscular dystrophyIII. Y-linked traitsIV. Mitochondrial traitsV. Three parent babyOutline of Current Lecture VI. Determining patterns of inheritanceVII. Predicting genetic risk using pedigreesa. exampleVIII. complications to pedigree analysisCurrent LectureDetermining Pattern of Inheritance- Mitochondrialo Offspring must have same status as mother (mother unaffected, all children must be unaffected & vice versa)- Y-linkedo No females affectedo Sons must have same status as father- X-linked dominanto Often more females affected than maleso Affected males must transmit trait to all daughterso Affected males must have affected motherso Affected females must have affected parents- X-linked recessiveo More males should be affected than femaleso Affected females must have affected sonso Affected females must have affected fathers- Autosomal dominanto Trait expressed in males and females in roughly equal proportionso Affected individuals must have at least one affected parento Offspring of affected parents can be unaffected- Autosomal recessiveo Trait expressed in males and females in roughly equal proportionso Unaffected parents may have affected childo Offspring of two affected parents must be affectedPredicting 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 childwill be affected by cystic fibrosis (autosomal recessive disease).- Probability their child will be affected?o Neither parent is affectedo Rr x RRo 0% chance- Rr x Rro 25% chance- R__ x Rro Look at parents’ pedigrees o Set up punnett square for dad’s parentso 2/3 chance, because rr not possibleo 2/3 x 1 x ¼= 1/6- R__ x R__o Punnett squares for both grandparentso 2/3 x ½ x ¼= 1/12Complications to pedigree analysis- Heteroplasmyo Situation in which, within a single cell, there is a mixture of mitochondria, some containing mutant DNA and some containing normal DNAo Variable expressivity based on numbers of mutant mitochondria- Conditions that manifest late in lifeo Individuals may not be symptomatic at the time the pedigree is constructedo Individuals may pass away from unrelated causes before they are symptomatico 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:-