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Lecture 2

BIOC15 Lecture 2 Friday September 6.doc

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University of Toronto Scarborough
Biological Sciences
Karen Williams

BIOC15 Lecture 2 Friday September 6, 2013  Genetics: gene □ We can detect and how a gene is acting by evidence of what we see of something else changing (a different of protein, a metabolism that is changing, a change in development) □ Can look at the level of the gene by asking about the function of the gene - If you have a normal biochemical pathway (normal gene  normal gene product) - Change in DNA ( abnormal gene  abnormal gene product); biochemical pathway is altered  Diagram □ If a parent brings a small patient into the doctor, small patient says she has urine that turns black - This is considered a disorder (not normal); alkaptonuria - Block in the pathway  Homogentistic acid (HA) accumulates  Phenylketonuria (PKU) □ At another point of the pathway □ Disorder that is connected (similar) to the pathways of alkaptonuria □ OMIM 261600 - Can see a little bit more - Biochemical features, inheritance and mapping, diagnosis, clinical management - Animal Model • McDonald et al. (1990) isolated mutant mice exhibiting hereditary hyperphenylalaninemia after ethylnitrosourea (ENU) of the germ line • By linkage mapping, they demonstrated that the disorder, which had other characteristics close to those of phenylketonuria mapped to mouse chromosomes 10 at or near the Pah locus • Also tells you how you can study a human disorder by making a animal model of the disease and looking a the genetics of that disorder in the animal model • Animal models can use mutagenesis to change the normal gene product in order to get that mouse model of phenylketonuria (can alter DNA and look for mice with phenotypes as in people) □ Phenylalanine hydroxylase (PAH)is used to change phenylalanine to tyrosine □ Therefore phenylalanine accumulates  How does a mutant allele affect a gene product? □ Solution (always define your terms: ex. P = PKU ) NORMAL ALLELE - Children: 100% PpHh - Grandchildren: 25% PPHh, 25% PPhh, 25% PpHh, 25% Pphh - Children: 100% normal - Grandchildren: 50% normal, 50% alkaptonuria (AKU) - Pphh (unusually genotype) therefore you assume what is most likely which is homozygous dominant at the normal (P) locus - When doing genetics problem do not assume most unlikely circumstance (if you need to make that assumption, it is usually given to you) - Pedigree is done in diamonds because sex is unknown (Two shaded in; affected individuals) - 0% of grandchildren have PKU (ppHH) why? • They all have at least one dominant allele • The mother cannot pass on a recessive allele because she does not have one □ Phenylalanine Tyrosine Carbon dioxide   P H  Alkaptonuria □ Normal enzymes are involved □ Under HA oxidase (5) converts homogentistic acid (HA) to maleylacetoactic acid □ Eventually after a few more enzymes it is converted to carbon dioxide and water □ Other enzymes are okay, it is just HA oxidase that is changed in alkaptonuria  gene product is defective or missing, there is no conversion □ HA accumulates and when it is exposed to air, you get black urine □ HA oxidase is dysfunctional in alkaptonuria  Beadle and Tatum used Neurospora crassa □ Metabolic genetics and metabolism wok comes from working on a bread mould □ The fungus Neurospora crassa; fungi can grow with complete medium or on minimal medium if it is a wild type fungus □ Haploid  How to grow a mould □ Minimal medium: simplest more basic nutrients needed for growth  Nutritional mutants □ If you zap mold with X-rays and select for ability to grow on minimal media (zap then put on complete medium, then again on minimal medium; find some that don’t grow  nutritional mutants) □ What nutrient is missing? - If amino acid is missing, would I see growth? - In a systematical way, Beadle and Tatum took nutritional mediums that grew on minimal medium and added some amino acids (ex. tryptophan) - Found that the mutant grew when tryptophan was added meaning it was deficient in the ability to use tryptophan  auxotropic for that amino acid - Another example with arginine  Inducing variation in growth ability □ Proto – first, auxo- without; troph – growth  Growth response and pathway inferred from data □ Can infer pathway from data you get where the nutritional mutant actual
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