ZOL 141 1st Edition Lecture 15 Outline of Last Lecture I Five patterns of inheritance II Autosomal Recessive a Patterns that suggest this b Example cystic fibrosis III Sex linked traits Outline of Current Lecture IV X linked dominant traits A Ex XLH V X linked recessive traits a Duchenne muscular dystrophy VI Y linked traits VII Mitochondrial traits VIII Three parent baby Current Lecture Patterns of Inheritance Cont d X linked Dominant traits Patterns that suggest inheritance of rare X linked dominant traits 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 one affected parent Assigning genotypes o 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 phosphate o Treatment Medication to increase levels of phosphate Surgical or orthopedic treatment X linked recessive traits Patterns that suggest inheritance of rare X linked recessive traits o More males affected than females o Affected females must have affected sons o 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 dystrophy o 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 males o Causes Mutation in DMD gene that prevents productions dystrophin Dystrophin helps stabilize and protect the membrane of muscle cells during mechanical stress of muscle contraction o Treatment There is no known cure Treatment aims to control symptoms to improve qualities of life Y linked traits Patterns that suggest inheritance of Y linked traits o No females will be affected o Sons must have same status as their father o Paternal inheritance o No convention used for genotyping pedigrees for Y linked traits Y chromosome contains about 60 genes o Many involved in male sex determination and development Y chromosome infertility o Condition that affects production of sperm o Produce little or no sperm abnormally shaped sperm or non motile sperm o Men are usually not affected by other symptoms Mitochondrial traits Mitochondria o Organelles that produce ATP which powers many cellular functions o Evolved from free living bacteria billions of years ago o Only organelle to contain its own genome o Small circular chromosome o Encodes 37 genes all essential for normal mitochondrial function o High mutation rate o Non mendelian maternal inheritance o 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 mother o Maternal inheritance o No convention used for genotyping pedigrees for mitochondrial traits o 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 affected o Heteroplasmy situation in which within a single cell there is a mixture of mutant DNA and normal DNA mitochondria o Variable expressivity based on numbers of mutant mitochondria Three parent baby Involves transferring nuclear material from egg of woman with mutant mitochondria into another woman s healthy egg for fertilization