ZOL 141 1st Edition Lecture 13 Outline of Last Lecture I. Genes and ChromosomesII. Mendelian inheritance in humansA. PedigreesB. Albinisma. Symptomsb. causesC. Hereditary Deafnessa. Symptomsb. causesIII. Principles of Independent AssortmentIV. Branch DiagramsOutline of Current Lecture V. PedigreesVI. Patterns of Inheritancea.Autosomal dominant traitsi.Ex: achondroplaysiaii.Ex: Marfan SyndromeCurrent LectureLecture 13: Pedigree Analysis in Human GeneticsWhat is a pedigree?- Diagram that depicts the members and relationships of a family using standardized symbols.Why are pedigrees constructed?- To determine the pattern of inheritance of a traito Difficult to find the gene responsible for a specific trait or diseaseo Cant make controlled genetic crosses in humanso Pedigrees often best option- To predict genetic risko Pregnancy outcomes o Adult-onset disorderso Risk of occurrence/recurrence in future childrenPedigree Symbols- Proband: first affected family member who seeks medical attention for genetic disorder- When possible, men are placed to left of woman in a mating.Patterns of InheritanceFive basic patterns of Mendelian inheritanceExamples of human traits controlled by single geneAutosomal Dominant traits- Autosomal: trait that originates from a gene found on any of the chromosomes that aren’t sex chromosomes- Complete dominance: condition in which heterozygote expresses trait in same manner as homozygote for particular allele. Allele or corresponding phenotypic trait expressed in heterozygote is said to be dominant- Dominance in humans: o change in phenotype that results in individuals from having one alleleo in many cases the phenotype of a homozygous dominant individual differs from that of a heterozygoteo often no distinction between complete dominance and codominance- Ex: Achondroplasia (short limbed dwarfism)o Symptoms: Short stature: average sized trunk, short arms and legs Enlarged head with prominent forehead Homozygous individuals are usually stillborn or die shortly after birtho Causes: Mutations in FGFR3 gene that lead to an overly active fibroblastgrowth factor receptor 3 protein FGFR3 protein regulates one growth by limiting formation of bone from cartilage particularly in long boneso Treatment: There are no consequences in terms of survival for heterozygotes Heterozygous parents have 25% chance of having a child homozygous for mutant allele- Autosomal dominant traitso Patterns that suggest autosomal dominant inheritance of rare traits: Trait is expressed in males and females in roughly equal proportions All affected individuals have at least one affected parent; all generations Offspring of affected parents can be unaffectedo Assigning genotypes When considering autosomal traits, an uppercase letter represents a dominant allele and a lowercase letter represents a recessive allele- Ex: Marfan Syndromeo Symptoms: Tall and slender, elongated fingers/toes and arm span> exceedsbody height Vision problems often caused by dislocated lens Defects in aorta causing it to weaken/stretcho Causes: Mutations in FBN1 gene that leads to reduction in available Fibrillin-1 protein Important for providing strength and flexibility to connective tissueso Treatment: No known cure Medicines that help heart beat slower and with less force, routine tests to check the heart, surgery to repair
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