ZOL 141 1st Edition Lecture 11 Outline of Last Lecture I Experimental Setup II Experiments and Results III Branch Diagram a Probability Rules IV Probability Outline of Current Lecture II Genes and Chromosomes III Mendelian inheritance in humans A Pedigrees B Albinism a Symptoms b causes C Hereditary Deafness a Symptoms b causes IV Principles of Independent Assortment V Branch Diagrams Current Lecture Mendel s Laws and Meiosis Genes are on chromosomes Chromosome theory of inheritance 1903 Sutton and Boveri independently proposed genes must be located on chromosomes Genes vs chromosomes Independent assortment occurs in metaphase 1 After meiosis 1 cells are haploid N 2 Mendelian inheritance in humans Pedigree Albinism o Symptoms Reduction in amount of melanin pigment formed in the skin hair and or eyes All forms are associated with vision problems Occur in all racial and ethnic groups 1 18000 people in US o Causes Oculocutaneous albinism OCA1 Mutation in TYR gene that encodes enzyme tyrosinase Tyrosinase converts tyrosine into melanin o Autosomal recessive Have one wild type normal allele can make enough pigment for normal coloring Homozygotes for mutant allele have albino phenotype Unaffected individuals can have affected child Principle of segregation o Heterozygous carrier o Gamete formation equal chance either allele by parents o Gamete combinations represent random fertilization o Same as peas Hereditary deafness o Symptoms Hearing loss inherited by children from their parents Syndromic associated with other symptoms Non syndromic not associated with other symptoms 1 1000 children in US 50 genetic o Causes Mutations in many genes can cause hereditary deaness GJB2 gene encodes gap junction beta 2 connexin 26 Important function in cochlea Cochlea converts physical vibrations Autosomal recessive Principle of independent assortment o Parents heterozygous for albinism A a o Heterozygous for deafness D wild type dominant and d mutant recessive o 9 16 pigmented and hearing o 3 16 pigmented and deaf o 3 16 albino and hearing o 1 16 albino and deaf Branch diagram same as peas