BCOR 101. WEEK 11
BCOR 101. WEEK 11 BCOR 101
Popular in Genetics
Popular in BioInformatics
verified elite notetaker
This 45 page Class Notes was uploaded by Katarina Fielding on Sunday April 24, 2016. The Class Notes belongs to BCOR 101 at University of Vermont taught by Amanda Yonan in Spring 2016. Since its upload, it has received 20 views. For similar materials see Genetics in BioInformatics at University of Vermont.
Reviews for BCOR 101. WEEK 11
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 04/24/16
Analysis and Mapping in Bacteria and Phages Chapter Six Bacteria • Single celled organisms • Usually reproduce asexually – Producing billions of genetically identical cells • Single, circular haploid genome – All mutations are expressed in phenotype • Have adapted to exchange and recombine genetic information with unrelated cells – To allow faster evolution • Recombination allows genetic mapping Conjugation • Genetic material from one bacterium cell is transferred to another bacterium • Akin to sexual reproduction, except: – One or a few genes – Replaces genes in one strain with other strain Conjugation This experiment proved conjugation can occur F (fertility) Factor • Some cells can donate their genetic material, but other cells cannot • F+ : cells that can donate DNA • F- : cells that can only receive DNA • F+ cells produce a “sex pilius” which makes physical contact with other cell – A tubular extension of the cell membrane • F factor physically moves into F- cells – Making both cells F+ F factor • Separate, smaller circular chromosome: – Double stranded DNA ~100,000 nucleotides 19 genes – Coding for: Genetic transfer and pilius formation High Frequency Recombination • Hfr = a mutated strain of bacteria that undergoes recombination 1000 X’s faster • Interrupted mating: – Hfr and F- strains mixed – Incubated for varying times – Then sheared apart in a blender • Saw that the genes always recombined in a certain order ex azi then ton then lac+ Chromosome Mapping • Hfr showed an ordered transfer of genes • Suggests that chromosome was transferred linearly • Gene order and genetic distance can be determined by measuring time Chromosome Mapping • Reran interrupted mating with four different Hfr strains • Saw different order of gene transfer – Or did they? Look for the pattern. Draw circle. What is the Hfr strain? • F factor gets integrated into bacteria’s genome • Site of integration becomes O site – Always the first part to recombine • F factor itself is the last part to recombine • Therefore any genes in the bacteria’s genome can be mapped based on time conjugation and recombination require Integration Conjugation Interrupted Conjugation • F- cell picks up some bacterial genes – Becoming partially diploid • Because mating is interrupted almost never picks up the F factor – Furthest away from O site – Therefore, F- cell does not become F+ • Hfr cell is unchanged after conjugation • Examining genes picked up by F- allows genetic mapping of bacterial genes Chromosome Mapping Example: • In three Hfr x F crosses (all Hfr strains derived from one F strain), the first three markers of transfer from interrupted mating experiments are: Hrf1: QDE... Hfr2: SCE... Hfr3: SFQ... • What is the order of genes on the circular bacterial chromosome (with S placed at both ends to represent circularity)? Hfr F′ • The process of integration can be reversed and the integrated F factor can be excised back out randomly • Excised F factor frequently retains some of bacterial genes with it F′ • F′ cells can go through conjugation with F- cells • In this case the chromosomal genes from the initial bacterium can be transferred through conjugation F- again partially diploid Plasmids • Independent, double stranded, circular DNA that exists in cytoplasm – In bacteria all DNA is cytoplasmic • Contain multiple genes • Classified based on type of genes: ex F factor = plasmid with genes for Fertility • Copied and distributed to daughter cells along with host DNA during mitosis R plasmids • Confer resistance antibiotics that would normally kill bacteria cells • Through conjugation these R plasmids can be transferred to non-resistant bacteria – Producing “super bugs” – Cannot be treated with multiple antibiotics Col Plasmid • Non-transferable plasmid – Not normal plasmid type • Encoding toxins that will kill neighboring bacteria cells • Bacteria that carry the Col plasmid (Col+) are immune to these toxins – “genetic warfare” between cells Note: Most plasmids are used for research – Genes carried are controlled by scientists Tranformation • Process where foreign DNA is stably integrated into the bacterial genome – Remember how Hfr was produced • Difference is that foreign DNA is integrated at homologous sequence in the genome – Not integrated randomly as F factor • Numerous steps, but only two categories: 1. DNA entry into host cell 2. Recombination btwn foreign DNA and genome Transformation Transformation Details • Competence: when a population of bacteria cells can accept foreign DNA – Can occur naturally – Or be induced for genetic studies • DNA strand aligns to homologous sequence and crossing over occurs • Replacing original host sequence – Which is then degraded • Heteroduplex: double stranded DNA that is a mix from two different sources Genetic Linkage • If two (or more) genes are linked they will often be co-transformed simultaneously • Because they are located on the same transforming segment of DNA • If two genes are not linked they will be transformed independently • Therefore, studying frequency of co- transformation can allow gene mapping Bacteriophages • Viruses that infect bacteria cells • Bacteria cells = host Bacteriophages – Lytic Phase All host cells die after lysis >200 live viruses released Viruses can then infect surrounding bacterium Bacteriophages – Lysogenic Phase • Some virus can also be integrated into host genome • As bacteria is replicated, viral DNA will be too • Lysis can be induced under certain conditions Lederberg-Zinder Experiment Prevents conjugation Transduction • When bacterial genetic material is recombined through phage infection • Occurs through the phage’s integration of it’s genome into the host cell’s genome through the lysogeny • If phage carries some bacterial genes in it’s genome along with it’s own genes – Some bacterial DNA picked up by virus Transduction • In step 4 some phages pick up part of the bacterial genome • When this phage infects another cell it carries the first DNA to a new host • Bacterial genes are integrated at homologous sequences into the host cell’s genome Transduction Mapping • If two (or more) genes are linked they will often be co-transduced simultaneously • Because they are located on the same transduced segment of DNA • If two genes are not linked they will be transduced independently • Therefore, studying frequency of co- transduction can allow gene mapping of bacterial genome Bacteriophage Recombination • Phage undergoes recombination too • Which allows for gene mapping of the few genes carried by bacteriophages 1. Mutants were identified in order to determine genes that existed in phage and their functions 2. Measure how often recombinant mutants are seen vs. total plaques Some of the Phage Mutants rapid lysis (r) More rapid and effective lysisected Mixed Infection Infect cells with two different mutant strains: ex h r+ x h+ r Bacteriophage Mapping • By studying mixed infection results – Mutants in two distinct strains of phage – Infecting same bacteria culture at once • Count the number of parental and recombinant plaques • If genes are unlinked parental and recombinant will be equally likely • If genes are linked, see an increase in parental plaques Bacteriophage Mapping • Determine map distance of bacteriophage’s genes by calculating RF • Recombination frequency (RF) Recombinant Plaques = % recombination Total Plaques • 1% recombination = 1 cM • Therefore mapping in phages is exactly the same as eukaryotic gene mapping Complementation Tests Questions? Discussion RecA Protein • If recA gene was mutated bacteria could not recombine • Therefore protein encoded by this gene must be necessary for recombination • RecA protein allows recombination between homologous sequences • Other genes and proteins also involved and necessary for recombination as well Map Distance 1.Chapter 7, Q 10 2.Chapter 7, Q 17 • Plus calculate Interference 3.Chapter 7, Q 14 4.Chapter 7, Q 15 • Plus calculate Interference Tetrad Analysis Parents Offspring a + x + b a + a b a + a + a b + b + b + + a b + b + + + + 105 20 32 Calculate distance between genes a and b. Co-transduction Two virus strains Infected bacteria + + + a b c + + + a c b Bacteria Selected Plaques + + + - 4100 a c b a b c None 3990 + c b + b c a 740 a + + b 670 a c + a + c b 160 + + b + b + c 140 a + b a b + c 90 a c + + + c a 110 10,000 Map these three viral genes. Co-transformation + + + Donor bacteria (a b c ) transforms recipient bacteria (a b c ): a+b-c- 180 a-b+c- 150 a+b+c- 210 a-b-c+ 179 a+b-c+ 2 a-b+c+ 1 a+b+c+ 3 Draw the general map of these three genes Hfr Interrupted Mating Hfr Order of Transfer 1 e r i u m b 2 u m b a c t 3 b m u i r e 4 c t e r i u 5 r e t c a b Starting with “B” draw a map of the bacterial genes. On your map draw where each strain inserted and which direction it inserted.
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'