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Lecture 2

BIOC15Fall2013 Lecture 1 and Lecture 2 Notes 2.13.29 PM.docx

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Biological Sciences
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Karen Williams

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BIOC15Fall2013 Lecture 1 and Lecture 2 Notes (Chapter 1 and Chapter 7.3) Lecture 1: Introduction to Genetics o In order to study genetics, we use a different number of model organisms, like rats, fruit flies and have them breed (controlled) o Central Dogma of Biology  transfer of information occurs through DNA replication, transcription and translation o Genetics  the science that deals with the structure and function of genes and their transmission from one generation to the next (heredity) Variation o Most of genetics involves the study of variation in traits o Trait (character) = the characteristics of an individual o Variants are those individuals in a species that differ in some characteristic from the vast majority of that species o Example: Mendel used flower colour variant (purple and white flowered pea plants) Genes o Gene  a nucleotide sequence of DNA that specifies a polypeptide or RNA o They are the DNA regions that encode proteins o DNA (normal gene)  normal protein gene product  normal phenotype o Mutational event in DNA  mutated gene  abnormal (partially functional or non functional) or no protein gene product  altered phenotype o DNA dictates the sequence of amino acids in a polypeptide chain, and the sequence then dictates the 3D shape of the polypeptide chain  the shape then dictates interactions and so on Chromosomes o DNA molecules carrying the genes are assembled into chromosomes  package and manage the storage, duplication, expression and evolution of DNA o Autosomal chromosomes  not involved in germinating traits (non sex chromosomes) o the entire collection of chromosomes in each cell = genome Molecular Similarities of All life forms o RNA used to be the molecule of information storage but it is intrinsically unstable o DNA took over the same functions as RNA o All organisms today descend from the first organism that happened upon the molecular specialization of information storage in DNA and biological function in proteins o Common origin  all living forms use the same genetic code in which various triplet grouping of the 4 letters of DNA and RNA encode the 20 letters of the amino acid alphabet o Pax6 gene  mutation leads to failure of eye development in both people and mice  gene that initiates eye development in vertebrates and insects Modular Construction of Genomes o Exons are arranged into genes  genes duplicate and diberfe to generate multigene families  multigene families sometimes rapidly expand to gene superfamilies containing hundreds of related genes (closely related but slightly divergent genes) o This is how evolution occurs at the molecular level o In eukaryotes, separated exons composing single gene allow potential rearrangements and rapid divesification Albinism o is an autosomal recessive trait o In most people the cells in the skin can produce melanin  this results in a range of skin pigments o Rare mutations result in complete lack of pigment  albinism o The dominant allele A determines the ability to make pigment o AA  active enzyme  pigmented o Aa  active enzyme  pigmented o aa  inactive enzyme  albino Alkaptonuria (AKU) o 1902 doctor Garrod noticed patients with AKU had unusual constituent to their urine = homogenistic acid (HA) o he described this disease as ‘inborn error of metabolism’ 1 o 1958  described the defective enzyme as homogenistic oxidase (HA oxidase) Phenylketonuria (PKU) o Foling (1934)  PKY is a disorder of metabolism caused by a defect in phenylalanine hydroxylase (PAH) o The role of the normal allele is to produce phenylalanine hydroxylase o Role of the normal gene is thus revealed by what happens when the normal gene product is absent! o o PKU  defective/missing PAH (phenylalanine hydroxylase) that turns phenylalanine into tyrosine o AKU  defective/missing HA oxidase that turns homogenistic acid (HA) into maleylacetoacetic acid  build up of HA = black pee (pathway is stopped) o Albinism  missing enzyme that turns tyrosine to dopamine (which can then make melanin a few steps later) How does a mutant allele affect a gene product? o A person with PKU marries one with AKU. One of their children marries a person with AKU. What genotypes and phenotypes of children can they have and in what proportions? o ppHH(person with PKU) x PPhh (person with AKU)  PpHh (100%) o PpHh (child of AKu and PKU parents) x PPhh (person with AKU)  PPHh, PPhh, PpHh, Pphh o So offspring  0% have PKU, 50% have AKU o Phenylalanine is converted to tyrosine by allele P, and tyrosine is converted to carbon dioxide by allele H Model Organisms o Selected by researchers b
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