EFB 307 Week 2
EFB 307 Week 2 EFB 307
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This 7 page Class Notes was uploaded by Gabrielle Donnelly on Sunday September 13, 2015. The Class Notes belongs to EFB 307 at Syracuse University taught by Dr. Powell in Fall 2015. Since its upload, it has received 27 views. For similar materials see Principles of Genetics in Biomedical Sciences at Syracuse University.
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Date Created: 09/13/15
September 8 2015 Mendelian analysis Gregor Mendel father of genetics Christian monk in a monastery dedicated to the teaching and doing of scienti c research 0 Published his ndings in 1866 but not recognized until 30 years later 0 Applied the scienti c method 0 Observe background datagtform hypothesisgtperform experimentgtform conclusions 0 Goal is to disprove hypothesis if you cannot then it is supported Cell cycle 0 Cells spend most time in G nonreplicating phase 0 In interphase chromatin spread open for gene expression Mitosis vs meiosis o Mitosisgt2n4 2 chromosome pairs Replication of DNA chromatins match upgtgtform 2 daughter cells 0 Meiosisgtsister chromatins exchange genetic material in metaphase and homologous chromosomes are separated Haploid cell is the result create gametes DNA exchange is evident in some gametes but does not occur in others 0 Variation meiosis differences in the formation of gametes in males vs females 4 sperm cells are formed in male meiosis Unequal distribution in cells for females to form ovum and polar bodies Terms to know 0 Gene fundamental physical and functional unit of heredity which carries information from 1 generation to the next DNA Allele on gene 1 of different forms of a gene that exists at a single locus 0 Different sequences can create different functions 0 Alleles form by mutation today39s mutation is tomorrow39s allele Locus location of a gene on chromosome Genotype speci c allelic composition of a cell Phenotype detectable outward manifestations of a speci c genotype traits Phenotype and genotype relationship Organisms phenotype is the phenotype of its cells 0 Cell phenotypegtinternal chemistry and structuregtcontrolled by enzymes 0 Enzyme function determined by its 3D structuregtcontrolled by amino acid sequence 0 Amino acid sequencegtDNA sequence of a geneGENOTYPE Therefore genotype DNA sequence determines phenotype outward appearance 0 Ex PKU human genetic disease Autosomal recessive gene Requires homozygous allele for disease Mental retardation and early death may occur Allele encodes a dysfunctional enzyme Homozygous alleles result in the inability to convert phenylalanine amino acid into tyrosine 00000 One gene one enzyme hypothesis 0 Most cellular components result from many enzymes catalyzing various intermediaries in biochemical pathway 0 This is why we observe epistasis gene interaction 0 Ex if genes 123 produce enzymes 139239339 all 3 are needed to produce chemical AgtBgtCgtD Also can have nonenzymatic gene products RNAs and structural proteins 0 A minority of genes produce more than 1 product by RNA splicing Ex epistasis in labgtbiochemical pathways products combine for nal phenotype Phenotypic variation 0 Continuous trait ranges over continuous spectrum 0 Ex human skin pigments European vs African vs mixedrace Discontinuous distinct characteristic trait 0 Ex rolling tongue attached earlobe Mendelian analysis used for both continuous and discontinuous Before Mendel Breeding was carried out somewhat successfully Prevailing theory quotblending of essencesquot between mother and father genes average Mendeldiscrete units of inheritancegtparticulate inheritancegene How did Mendel know Picked the right plant in peas they naturally self true breeding lines available picked traits not linked to one another 0 Made controlled crosses and carefully examined ratio of offspring More terms 0 Gene pair 2 copies of gene present in diploid cell Diploid cell with 2 chromosome sets 2 genomes Homozygous same allele in a given pair Heterozygous different alleles in a given pair Hemizygous single allele without paired gene in a diploid cell 0 X linked genes in XY males 0 Mutation insertion of deletion 0 Hybrid breeding from uneven crossovers 0 Genetic engineering 0 Acts like dominant gene Homolog gene related to a second gene common ancestral DNA sequence Ortholog genes in different species same function homologs Paralog genes related by duplication in genome evolve new functions homologs in same species Dominant genes that always show phenotype 0 Ability to roll tongue 0 0x0 gene put in Chestnut Recessive genes that show phenotype in absence of dominant alleles o Inability to roll tongue Crossing Monohybrid cross look at inheritance of single gene pair 0 YY true breeding yellow x yy true breeding green parental 0 Y and y gametes o Yy yellow heterozygous F1 rst lial generation 0 F2 generation has 121 genotypic ratio 31 phenotypic ratio Mendel39s 1st law 2 members of gene pair segregate from each other into gametes so 12 gametes carry 1 member of the pair and the 12 of gametes carry the other member of the pair Dihybrid cross RRyy round green x rrYY wrinkled yellow 0 9331 genotypic ratio Mendel39s 2 cl law during gamete formation the separation of alleles of 1 gene is independent of the segregation of the alleles of another gene 0 Law of independent assortment o Exceptionclosely linked genes Homozygous vs heterozygous Can39t tell with phenotype 0 Use test cross 0 Cross your unknown with a tester known genotype 0 Tester is homozygous recessive for gene Test cross 0 Unknown A and tester aa If AA phenotypic ratio of progeny be 1 all Aa If Aa phenotypic ratio of progeny be 11 12 Aa and 12 aa Determines if gene pair is hetero or homo Can be used with many different gene pairs must examine resulting phenotypic ratios individually OOOO Trihybrid cross inheritance of multiple traits P1 AABBCC and aabbcc Gametes ABC and abc F1 AaBch ABC ABc AbC etc Forked line methodbranch instead of Punnet square Ex method used in chestnut breeding with 3 resistance genes Mathematical gene crossing heterozygous pairs gametes genotype phenotypes n 2quotn 3quotn 2quotn 1 2 3 2 more genes more phenotype possibilities TAKE HOME QUESTIONS Genotypes more abundant with heterozygous crosses dominant allele hides recessive phenotype 3 in uences on phenotype which causes different nger prints Developmental noise 0 Sex determination in alligators is caused by what The environment 0 Human genome has how many genes 2400028000 September 10 2015 Probability Calculating genetic ratios 0 Use two statistical rulesgtcommit to memory Product rule 0 Probability of independent events occurring together product of probabilities of each individual event occurring 0 Ex Dice probability of rolling double sixes 136 16 x 16 0 If you rolled 3600 times you d get double sixes about 100 times Sum rule 0 Probability of either 2 mutually exclusive events occurring is the sum of their individual probabilities of occurring 0 Ex Dice probability of rolling number that add to 7 with 2 dice Die 1 Die 2 Probability 6 1 136 1 6 136 5 2 136 etc c There are 6 possibilities so 136 136 136 636 or 16 c For every 3600 rolls about 600 would have the dice add up to 7 Application to genetics Ex A plant with 3 gene pairs A produces anthocyanin bluered a does not produce anthocyanin Y normal green leaves y yellowgreen leaves P normal pollen formation p sterile male no pollen formation Cross two heterozygotes o AaYpr x AaYpr 0 What39s the probability of getting homozygous recessive in all gene pairs aayypp Having no anthocyanin yellowgreen leaves sterile male 1 Treat each trait separately and apply the product rule 0 Aa x Aa has a genotypic ratio of 121 or 1A for aa 0 This is the same for Yy and Pp crosses 2 Use the product rule 0 1A x 1A x 1A 164 plants will have completely recessive traits Q Probability of getting an anthocyanin producing yellowgreen male fertile plant Any o A 3A 14 AA 12 Aa 000000 0 30 14 o P 3A 0 3A x x 3A 964 Q What is the probability that a plant would have just 1 homozygous recessive trait aa yy or pp each are mutually exclusive events 0 Any 964 34 x 14 x 34 0 aaYP 964 14 x 3A x 3A o AYpp 964 34 x 3A x 14 o Added up 2764 Pedigree Analysis Family trees and Mendelian principles to deduce inheritance important for determining genetic diseases Large human families with good records work best 0 Ex Mormons 0 You can39t expect normal ratios due to small numbers Male square Female circle Sex unknown diamond Female carrier of sex linked recessive gene circle with dot in the middle the symbol will be colored lled in if the phenotype is present Order of birth goes from left to right Analysis Proband an individual who is the focus of a genetic study propositus Trait dominant or recessive 0 Look at recessive rst usually genetic diseases 0 Ex Recessive allele in albinism 0 Parents with full pigmentation can have kids with albinism H Both parents have Aa 5 e a g AA Aa Aa Other recessive diseases Hemophilia sexlinked lacking blood clotting factor Cystic brosis lungs ll up with mucus one of the most common genetic diseases in the US PKU error of metabolism resulting in mental retardation diet can control disease Sickle cell anemia hemoglobin mutated with low 02 carrying capacit at of n cause clumping 39 EX Grandparents AA or Aa and aa Parents Aa and Aa Q What39s he robability t at t 39 39 s o Aa a 55 f e r A aa A aa 0 14 AA x 12 Aa o 3 options AA Aa aAgtgt23 probability that they39re carriers Genetic diseases 0 Most caused by recessive alleles selected against normally Alleles are rare therefore homozygous recessive very rare 0 Some heterozygote traits can be bene cial Malaria resistance 0 Using HardyWeinberg principle pquot2 2pq qquot2 1 o For 2 alleles A and a Let p A39s proportion Let q a39s proportion Let pquot2 AA homozygous dominant Let 2pq Aa heterozygous Let qquot2 aa homozygous recessive Sickcell anemia o If allele occurs 1100 alleles how often do we see the disease occur 0 Heterozygous carriers 2pqgt 299100 represents alleles 1100 19810000 Or approximately 150 people have advantages 0 Homozygous recessive qquot2 1100quot2 110000 makes the disease rare If Inbreeding occurs 0 Increases the problem of homozygous recessive alleles being passed on 0 Reason why cousin marriage is not allowed Pedigree analysis of dominant alleles Dominant alleles phenotype shown in parents and offspring Abnormal homozygous dominant alleles are very rare because of detrimental added effects Ex Androplasia type of dwar sm o Polydactyly extra ngers and toes o Huntington s disease late onset of disease neurological disease premature death symptoms after children are born Pedigree determines odds o If 1 parent develops Huntington s you have 50 chance of developing it too 0 If 1 grandparent has the disease you have 25 change 12 x 12 1A1 0 Now there39s a genetic test for the disease Xlinked inheritance Many human genes are in the xchromosome xlinked Ex color blindness red 0 Hemizygous in males and acts like a dominant allele 0 Recessive in females 0 Q Woman with color blindness what is the probability her sons have it 100 because the alleles for it are on both of her Xchromosomes Categories of Inheritance Autosomal recessivegtalbinism Tay sachs Autosomal dominantgt Huntington s Ylinked gt hairy ears Xlinked recessive gt color blindness Xlinked dominant gt bone weakening disease Hypophosphatemia organelle