ZOL 141 1st Edition Lecture 13 Outline of Last Lecture I Genes and Chromosomes II Mendelian inheritance in humans A Pedigrees B Albinism a Symptoms b causes C Hereditary Deafness a Symptoms b causes III Principles of Independent Assortment IV Branch Diagrams Outline of Current Lecture V Pedigrees VI Patterns of Inheritance a Autosomal dominant traits i Ex achondroplaysia ii Ex Marfan Syndrome Current Lecture Lecture 13 Pedigree Analysis in Human Genetics What 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 trait o Difficult to find the gene responsible for a specific trait or disease o Cant make controlled genetic crosses in humans o Pedigrees often best option To predict genetic risk o Pregnancy outcomes o Adult onset disorders o Risk of occurrence recurrence in future children Pedigree 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 Inheritance Five basic patterns of Mendelian inheritance Examples of human traits controlled by single gene Autosomal 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 allele o in many cases the phenotype of a homozygous dominant individual differs from that of a heterozygote o 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 birth o Causes Mutations in FGFR3 gene that lead to an overly active fibroblast growth factor receptor 3 protein FGFR3 protein regulates one growth by limiting formation of bone from cartilage particularly in long bones o 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 traits o 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 unaffected o Assigning genotypes When considering autosomal traits an uppercase letter represents a dominant allele and a lowercase letter represents a recessive allele Ex Marfan Syndrome o Symptoms Tall and slender elongated fingers toes and arm span exceeds body height Vision problems often caused by dislocated lens Defects in aorta causing it to weaken stretch o Causes Mutations in FBN1 gene that leads to reduction in available Fibrillin 1 protein Important for providing strength and flexibility to connective tissues o Treatment No known cure Medicines that help heart beat slower and with less force routine tests to check the heart surgery to repair aorta