ZOL 141 1st Edition Lecture 15Outline of Last Lecture I. Five patterns of inheritanceII. Autosomal Recessivea. Patterns that suggest thisb. Example: cystic fibrosisIII. Sex linked traitsOutline of Current Lecture IV. X-linked dominant traitsA. Ex: XLHV. X-linked recessive traitsa. Duchenne muscular dystrophyVI. Y-linked traitsVII.Mitochondrial traitsVIII. Three parent babyCurrent LecturePatterns of Inheritance Cont’dX-linked Dominant traits- Patterns that suggest inheritance of rare X-linked dominant traits:o Often more females affected than maleso Affected males must transmit trait to all daughterso Affected males must have affected motherso Affected females must have one affected parent- Assigning genotypeso When considering X-linked traits, X^R represents a dominant allele and X^r represents a recessive allele.- X-linked dominant disorder: X-linked hypophosphatemia (XLH) (Low phosphate in the blood)o Symptoms: Low levels of phosphate in blood Affected individuals are shorter and have bone abnormalities (bowed legs, knock knees)Cause: - Mutation in PHEX gene- Unclear how mutations in this gene lead to low levels of phosphate in blood, likely due to an indirect effect that causes kidneys to excrete too much phosphateo Treatment: Medication to increase levels of phosphate Surgical or orthopedic treatmentX-linked recessive traits:- Patterns that suggest inheritance of rare X-linked recessive traits:o More males affected than femaleso Affected females must have affected sonso Affected females must have affected fathers- When considering X-linked traits, X^R represents a dominant allele and X^r represents recessive. Start with males- X-linked recessive disorder: Duchenne muscular dystrophyo Symptoms: Progressive muscle weakness and loss of muscle tissue, primarily skeletal and cardiac muscle Symptoms as early as age 3, often fatal in 20s Occurs almost exclusively in maleso Causes: Mutation in DMD gene that prevents productions dystrophin Dystrophin helps stabilize and protect the membrane of musclecells during mechanical stress of muscle contractiono Treatment: There is no known cure Treatment aims to control symptoms to improve qualities of lifeY-linked traits- Patterns that suggest inheritance of Y-linked traits:o No females will be affectedo Sons must have same status as their fathero Paternal inheritanceo No convention used for genotyping pedigrees for Y-linked traits- Y chromosome contains about 60 geneso Many involved in male sex determination and development- Y chromosome infertilityo Condition that affects production of spermo Produce little or no sperm, abnormally shaped sperm or non-motile spermo Men are usually not affected by other symptomsMitochondrial traits- Mitochondria:o Organelles that produce ATP which powers many cellular functionso Evolved from free-living bacteria billions of years agoo Only organelle to contain its own genomeo Small, circular chromosomeo Encodes 37 genes, all essential for normal mitochondrial functiono High mutation rateo Non-mendelian maternal inheritanceo Egg has a lot of mitochondria, sperm has none in head- Patterns that suggest mitochondrial inheritance of traits:o Offspring have same status as their mothero Maternal inheritanceo No convention used for genotyping pedigrees for mitochondrial traitso Pedigree one exams: affected mothers will have affected children- Disease associated with mutations in mitochondrial DNA:o In general, tissues with highest energy requirement are affectedo Heteroplasmy: situation in which, within a single cell, there is a mixture of mutant DNA and normal DNA mitochondriao Variable expressivity based on numbers of mutant mitochondriaThree parent baby- Involves transferring nuclear material from egg of woman with mutant mitochondria into another woman’s healthy egg for