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Laboratorium techniek 1 13 Genetics Heredity = Continuity of biological traits from one generation to the next parents children Who are the parents of.

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Presentation on theme: "Laboratorium techniek 1 13 Genetics Heredity = Continuity of biological traits from one generation to the next parents children Who are the parents of."— Presentation transcript:

1 Laboratorium techniek 1 13 Genetics Heredity = Continuity of biological traits from one generation to the next parents children Who are the parents of these children? Variation = Inherited differences among individuals of the same species Genetics = The scientific study of heredity and hereditary variation

2 Laboratorium techniek 2 13 Chromosome Offspring acquire genes from parents by inheriting chromosomes chromosomechromatine wound on histon peptide DNA double helix of nucleotides base pair phosphate desoxyribose N-base nucleotide gene locus DNA = Type of nucleic acid that is a polymer of four different kinds of nucleotides. Chromosomes = Organizational unit of heredity material in the nucleus of eukaryotic organisms Gene = Unit of hereditary information that is made of DNA and is located on chromosomes Locus = Specific location on a chromosome that contains a gene

3 Laboratorium techniek 3 13 Karyotype

4 Laboratorium techniek 4 13 Asexual life cycle Asexual reproduction A type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts

5 Laboratorium techniek 5 12 Mitosis l Mitotic cell cycle: In a dividing cell, the mitotic (M) phase alternates with interphase, a growth period. The first part of interphase, called G 1, is followed by the S phase, when the chromosomes replicate; the last part of interphase is called G 2. In the M phase, mitosis divides the nucleus and distributes its chromosomes to the daughter nuclei, and cytokinesis divides the cytoplasm, producing two daughter cells.

6 Laboratorium techniek 6 12 Mitosis ll

7 Laboratorium techniek 7 12 Mitosis lll

8 Laboratorium techniek 8 13 Sexual life cycle Meiosis and fertilization result in alternation between the haploid and diploid condition Diploid = Condition in which cells contain two sets (2n) of chromosomes Haploid = Condition in which cells contain one set (1n) of chromosomes Gamete = A haploid reproductive cell (sperm cells and ova) The diploid number is restored when two haploid gametes unite Fertilization = The union of two gametes to form a zygote Zygote = A diploid cell that results from the union of two gametes

9 Laboratorium techniek 9 13 Variety of life cycles Three basic patterns of sexual life cycles a. Animal In animals gametes are the only haploid cells b. Fungi and some protists In many fungi and some protists, the only diploid stage is the zygote c. Plants and some algae Plants and some species of algae alternate between multicellular haploid and diploid generations

10 Laboratorium techniek Life cycle malaria

11 Laboratorium techniek Life cycle Aspergillus

12 Laboratorium techniek (A)sexual reproduction Like begets like, more or less: a comparison of asexual versus sexual reproduction

13 Laboratorium techniek Meiosis – overview What happens during meiosis?

14 Laboratorium techniek Meiosis l

15 Laboratorium techniek Meiosis ll

16 Laboratorium techniek Mitosis vs. meiosis

17 Laboratorium techniek Origins of genetic variation l 1. Independent assortment of chromosomes Independent assortment = the random distribution of maternal and paternal homologues to the gametes The process produces 2 n possible combinations of maternal and paternal chromosomes in gametes

18 Laboratorium techniek Origins of genetic variation ll 2. Crossing over Crossing over = The exchange of genetic material between homologues; occurs during prophase of meiosis I. In humans, there is an average of two or three crossovers per chromosome pair

19 Laboratorium techniek Origins of genetic variation lll 3. Random fertilization Random fertilization is another source of genetic variation in offspring The process produces 2 n x 2 n possible combinations of maternal and paternal chromosomes in the zygote 4. Mutation The ultimate source of variation: random and relatively rare structural changes made during DNA replication in a gene as a result of mistakes

20 Laboratorium techniek Summary 1.Offspring acquire genes from parents by inheriting chromosomes 2.Like begets like, more or less 3.Fertilization and meiosis alternate in sexual life cycles 4.Meiosis reduces chromosome number from diploid to haploid 5.Sexual life cycles produce genetic variation among offspring 6.Evolutionary adaptation depends on a population’s genetic variation

21 Laboratorium techniek Key terms heredity karyotype zygote meiosis I and II variation homologous diploid cells synapsis genetics chromosomes meiosis tetrad gene sex chromosomes alternation of generations chiasma (chiasmata) asexual reproduction autosome clone gamete sporophyte crossing over sexual reproduction haploid cell sporeslife cycle fertilization gametophyte somatic cell syngamy

22 Laboratorium techniek Heredity Theories of heredity Blending theory of heredity = Pre-Mendelian theory of heredity proposing that hereditary material from each parent mixes in the offspring; once blended the hereditary material is inseparable and the offspring's traits are some intermediate between the parental types Particulate theory of heredity = Gregor Mendel's theory that parents transmit to their offspring discrete inheritable factors (now called genes) that remain as separate factors from one generation to the next

23 Laboratorium techniek Mendel’s experiments Terms Character = Detectable inheritable feature of an organism  gene Trait = Variant of an inheritable character  allele True breeding = Always producing offspring with the same traits as the parents when the parents are self-fertilized P = true-breeding parental plants of a cross F 1 = hybrid offspring of the P- generation F 2 = generation of self-pollinated F 1 -plants

24 Laboratorium techniek Monohybrid cross Monohybrid cross Hypothesis: If the inheritable factor for white flowers had been lost, then a cross between F1 plants should produce only purple- flowered plants. Experiment: Mendel allowed the F1 plants to self-pollinate. Results: There were 705 purple- flowered and 224 white-flowered plants in the F2 generation — a ratio of 3:1. Conclusion: The inheritable factor for white flowers was not lost, so the hypothesis was rejected

25 Laboratorium techniek Testing hypotheses using the  2 -statistic There were 705 purple-flowered and 224 white-flowered plants in the F2 generation. Hypothesis: Is this a ratio of 3:1? 1.Calculate expected values based on the result total (929): 3 : 1 = : Calculate the differences between observed (O) and expected (E) 3.Standardise the differences: |O – E | 2  2 =   E 4.Calculate degrees of freedom (DF) = number of differences – 1 5.Lookup in  2 table at DF 6.If p<0.05 then reject hypothesis O E |O–E| ( ) 2  2 =  +  The correction for continuity of 0.5 is only applied when DF=1  2 = = At DF= lies between and with 0.900>p>0.500, so accept hypothesis

26 Laboratorium techniek Law of segregation By the law of segregation, the two alleles for a character are packaged into separate gametes 1. Alternative forms of genes are responsible for variations in inherited characters. 2. For each character, an organism inherits two alleles, one from each parent. 3. If the two alleles differ, one is fully expressed (dominant allele P); the other is completely masked (recessive allele p). 4. The two alleles for each character segregate during gamete production.

27 Laboratorium techniek Genotype and phenotype Homozygous = Having two identical alleles for a given trait (e.g., PP or pp). Heterozygous = Having two different alleles for a trait (e.g., Pp). Phenotype = An organism's expressed traits (e.g., purple or white flowers). Genotype = An organism's genetic makeup (e.g., PP, Pp, or pp).

28 Laboratorium techniek Testcross Testcross = The breeding of an organism of unknown genotype with a homozygous recessive

29 Laboratorium techniek Dihybrid cross Mendel's law of independent assortment = Each allele pair segregates independently of other gene pairs during gamete formation

30 Laboratorium techniek Testing hypotheses using the  2 -statistic

31 Laboratorium techniek Laws of Probability Question: In a Mendelian cross between pea plants that are heterozygous for flower color (Pp), what is the probability of the offspring being a heterozygote? Question: In a Mendelian cross between pea plants that are heterozygous for flower color (Pp), what is the probability that the offspring will be homozygous recessive? 2. Rule of addition Rule of addition = The probability of an event that can occur in two or more independent ways is the sum of the separate probabilities of the different ways 1. Rule of multiplication Rule of multiplication = The probability that independent events will occur simultaneously is the product of their individual probabilities

32 Laboratorium techniek Extended Mendelian genetics l Incomplete dominance = dominant phenotype is not fully expressed in the heterozygote, resulting in a intermediate phenotype Complete dominance = an allele is fully expressed in the phenotype of a heterozygote and masks the phenotypic expression of the recessive allele; the phenotypes of the heterozygote and dominant homozygote are indistinguishable Codominance = full expression of both alleles in the heterozygote

33 Laboratorium techniek Extended Mendelian genetics ll Important points about dominance/recessiveness relationships: 1. They range from complete dominance, through various degrees of incomplete dominance, to codominance 2. They reflect the mechanisms by which specific alleles are expressed in phenotype and do not involve the ability of one allele to subdue another at the level of the DNA 3. They do not determine or correlate with the relative abundance of alleles in a population

34 Laboratorium techniek Extended Mendelian genetics lll Multiple alleles = Some genes may have more than just two alternative forms of a gene

35 Laboratorium techniek Extended Mendelian genetics l V Pleiotropy = The ability of a single gene to have multiple phenotypic effects Epistasis = Interaction between two nonallelic genes in which one modifies the phenotypic expression of the other (9:3:4)

36 Laboratorium techniek Extended Mendelian genetics V Polygenic inheritance = Mode of inheritance in which the additive effect of two or more genes determines a single phenotypic character

37 Laboratorium techniek Nature versus nurture Norm of reaction = Range of phenotypic variability produced by a single genotype under various environmental conditions The expression of most polygenic traits, such as skin color, is multifactorial; that is, it depends upon many factors - a variety of possible genotypes, as well as a variety of environmental influences

38 Laboratorium techniek Human genetics Humans are difficult to investigate long generation time few offspring experiments unacceptable Pedigree = A family tree that diagrams the relationships among parents and children across generations and that shows the inheritance pattern of a particular phenotypic character

39 Laboratorium techniek Human genetic disorders l Recessive disorders: show up in homozygous individuals heterozygote are called carriers frequencies differ worldwide due to local selective forces Cystic fibrosis Tay-Sachs disease Sickle cell anemia

40 Laboratorium techniek Human genetic disorders ll Phenylketonuria Dominant disorders Achondroplasia (dwarfism) 1:10,000 people Lethal dominant alleles are not passed to next generation Late-acting alleles escape elimination: Huntington’s disease Multifactoral disorders (heart disease, diabetes, cancer, schizophrenia)

41 Laboratorium techniek Genetic testing Carrier recognition Fetal testing Newborn screening (PKU)

42 Laboratorium techniek Summary 1.Mendel brought an experimental and quantitative approach to genetics 2.By the law of segregation, the two alleles for a character are packaged into separate gametes 3.By the law of independent assortment, each pair of alleles segregates into gametes independently 4.Mendelian inheritance reflects rules of probability 5.Mendel discovered the particulate behavior of genes 6.The relationship between genotype and phenotype is rarely simple 7.Pedigree analysis reveals Mendelian patterns in human inheritance 8.Many human disorders follow Mendelian patterns of inheritance 9.Technology is providing news tools for genetic testing and counseling

43 Laboratorium techniek Key terms character dominant allele polygenic inheritancetrait law of segregation true-breeding incomplete dominance multifactorial complete dominance homozygous monohybrid cross heterozygous cystic fibrosisP generation multiple alleles F 1 generation genotype pleiotropy F 2 generation testcross alleles dihybrid cross recessive allele hybridization norm of reactioncarriers codominanceepistasis phenotypesickle-cell disease quantitative characterlaw of independent assortment

44 Laboratorium techniek Chromosomal basis of inheritance Chromosome theory of inheritance: Mendelian genes have specific loci on chromosomes, which undergo segregation and independant assortment Recombinants have new combinations of traits RY and ry are parental phenotypes rY and Ry are recombinant phenotypes

45 Laboratorium techniek Morgan’s experiments with fruit flies l Morgan used Drosophila melanogaster, a fruit fly species Short generation time Fruit flies have three pairs of autosomes and a pair of sex chromosomes (XX in females, XY in males) The normal character phenotype is the wild type Alternative traits are mutant phenotypes

46 Laboratorium techniek Morgan’s experiments with fruit flies ll Cross white-eyed male with a red- eyed female: F 1 had red eyes Crosses between the F 1 offspring produced the classic 3:1 phenotypic ratio in the F 2 offspring The white-eyed trait appeared only in males All the females and half the males had red eyes Morgan concluded that a fly’s eye color is a sex-linked gene

47 Laboratorium techniek Linked genes Dihybrid test cross did not produce 1:1:1:1 ratio  genes must be on the same chromosome: linked genes Complete linkage gives ratio 1:1:0:0 17% recombinants must be the result of crossing over

48 Laboratorium techniek Crossing over Recombination is result of crossing over and independant assortment

49 Laboratorium techniek Genetic maps Geneticists can use recombination data to map a chromosome’s genetic loci: linkage map The farther apart two genes are, the higher the probability that a crossover will occur between them and therefore a higher recombination frequency The recombination frequency between cn and b is 9% The recombination frequency between cn and vg is 9.5% The recombination frequency between b and vg is 17% How are the loci arranged? b – vg – cn or vg – b - cn Map distance: 1 unit is 1% recombination

50 Laboratorium techniek Genetic maps Why is 9,0 (b-cn)+ 9,5 (cn-vg) > 17% (b-vg)? This results from multiple crossing over: the further loci are apart, the greater the change for multiple crossing over events Some genes on a chromosome are so far apart that a crossover between them is virtually certain: independent inheritance, no linkage

51 Laboratorium techniek Sex chromosomes

52 Laboratorium techniek 52 Summary 1.Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles 2.Morgan traced a gene to a specific chromosome 3.Linked genes tend to be inherited together because they are located on the same chromosome 4.Independent assortment of chromosomes and crossing over produce genetic recombinants 5.Geneticists use recombination data to map a chromosome’s genetic loci 6.The chromosomal basis of sex varies with the organism 7.Sex-linked genes have unique patterns of inheritance 8.Alterations of chromosome number or structure cause some genetic disorders 9.The phenotypic effects of some mammalian genes depend on whether they are inherited from the mother or the father (imprinting) 10.Extranuclear genes exhibit a non-Mendelian pattern of inheritance

53 Laboratorium techniek Key terms chromosome theory of inheritance linkage map polyploidycytological map deletionwild type duplicationmutant phenotype hemophilia inversion sex-linked genes Barr body translocationlinked genes nondisjunction Down syndrome genetic recombination aneuploidy fragile X syndromeparental type trisomicrecombinants monosomic

54 Laboratorium techniek Genetics of viruses and bacteria Bacteria are prokaryotic organisms: - small - no compartments - single, circular chromosome Viruses are smaller and simpler still, lacking the structure and most meta- bolic machinery in cells - aggregates of nucleic acids and protein - genes in a protein coat - reproduce in host-cells - limited hoste-range Ideal genetic models for study

55 Laboratorium techniek Discovery of viruses The discovery of Tobacco Mosaic Virus TMV Ultimate pathogen test: Postulates of Koch 1886 Mayer: very small, invisible, non- culturable bacterium? 1892 Ivanowsky: pathogen passed porcelain filter – small bacterium or toxin? 1898 Beijerinck: infectious agent reproduces in living host, is soluble, not killed in ethanol – named micro-organism virus 1935 Stanley: crystallized the pathogen 1939 Kaushe et al: first electron micrograph, particle is only 20 nm in diameter 1939 today TMV particle consists of nucleic acid enclosed by a protein coat

56 Laboratorium techniek Viral structure 1 Viral genome ds DNA, ss DNA, ds RNA or ss RNA Single nucleic acid molecules that are linear or circular May have four to hundreds of genes 2 Capsids Capsid = Protein coat that encloses the viral genome, composed of many capsomeres Nucleocapsid = integrated structure of nucleic acid and capsid-proteins

57 Laboratorium techniek Viral structure 3 Envelopes or membranes Envelope = Membrane that cloaks some viral capsids Helps viruses infect their host by fusing with cell-membrane Derived from host cell or nuclear membrane which is usually virus-modified They also have some viral proteins and glycoproteins

58 Laboratorium techniek Bacteriophages The most complex capsids are found among bacteriophages Of the first phages studied, seven infected E. coli. These were named types 1 – 7 (T1, T2, T3,... T7). The T-even phages – T2, T4, and T6—are structurally very similar The icosohedral head encloses the genetic material The protein tailpiece with tail fibers attaches the phage to its bacterial host and injects its DNA into the bacterium

59 Laboratorium techniek Infection cycle Viral infection begins when virus genome enters the host cell Once inside, the viral genome commandeers its host, reprogramming the cell to copy viral nucleic acid and manufacture proteins from the viral genome Nucleic acid molecules and capsomeres self-assemble into viral particles that exit the cell

60 Laboratorium techniek Phage lytic cycle In the lytic cycle the phage kills the host. Virus is called virulent.

61 Laboratorium techniek Defenses against phages Natural selection favors bacterial mutants with receptors sites that are no longer recognized by a particular type of phage Bacteria produce restriction nucleases that recognize and cut up foreign DNA, including certain phage DNA Modifications to the bacteria’s own DNA prevent its destruction by restriction nucleases But, natural selection favors resistant phage mutants.

62 Laboratorium techniek Phage lysogenic cycle In the lysogenic cycle phage DNA incorporates in bacterial DNA: prophage. Virus is called temperate.

63 Laboratorium techniek Replication strategies in plant and animal viruses –RNA and retroviruses have viral enzymes in nucleocapside RNA-viruses have high mutation rates (no proof-reading during replication)

64 Laboratorium techniek Animal viruses

65 Laboratorium techniek Retrovirus HIV causes AIDS (Acquired Immuno Deficiency Syndrome) HIV is a retrovirus

66 Laboratorium techniek Viruses and symptoms The link between viral infection and the symptoms it produces is often obscure –Virus triggers release of hydrolytic enzymes from lysosomes –Viruses causes the infected cell to produce toxins that lead to disease symptoms –Virus has toxic molecular components (envelope proteins) In some cases, viral damage is easily repaired (respiratory epithelium after a cold), but in others, infection causes permanent damage (nerve cells after polio) Cure by immune system, some medicines: –AZT interferes with reverse transcriptase of HIV –Acyclovir inhibits herpes virus DNA synthesis –antibiotics are useless Prevention by vaccination RNA-viruses are hard to combat, because they mutate fast Disease Cause major losses

67 Laboratorium techniek Plant viruses l Plant viruses are classified according to ICTV guidelines: Type of nucleid acid Form Host The Current Classification of Plant Virus Genera* *abstract

68 Laboratorium techniek Plant viruses ll Plant viral diseases are spread by two major routes: Horizontal transmission: infection by an external source –Plants are more susceptible if their protective epidermis is damaged, perhaps by wind, chilling, injury, or insects. –Insects are often carriers of viruses, transmitting disease from plant to plant non-persistent: insect is infectious for short time persistent: insect remains infectious for long period or forever (propagates in insect) Vertical transmission: a plant inherits a viral infection from a parent –This may occur by asexual propagation or in sexual reproduction via infected seeds

69 Laboratorium techniek Plant viruses lll Once it starts reproducing inside a plant cell, virus particles can spread throughout the plant by passing through plasmodesmata Agricultural scientists have focused their efforts largely on reducing the incidence and transmission of viral disease and in breeding resistant plant varieties

70 Laboratorium techniek Where did viruses come from? Candidates for the original sources of viral genomes include plasmids and transposons –Plasmids are small, circular DNA molecules that are separate from chromosomes –Plasmids, found in bacteria and in the eukaryote yeast, can replicate independently of the rest of the cell and are occasionally be transferred between cells –Transposons are DNA segments that can move from one location to another within a cell’s genome Both plasmids and transposons are mobile genetic elements

71 Laboratorium techniek Viroids Viroids, smaller and simpler than even viruses, consist of tiny molecules of naked circular RNA that infect plants Their several hundred nucleotides do not encode for proteins but can be replicated by the host’s cellular enzymes These RNA molecules can disrupt plant metabolism and stunt plant growth, perhaps by causing errors in the regulatory systems that control plant growth Potato spindle tuber viroid

72 Laboratorium techniek Prions Prions are infectious proteins that spread a disease They appear to cause several degenerative brain diseases including scrapie in sheep, “mad cow disease”, and Creutzfeldt-Jacob disease in humans normal disease-causing According to the leading hypothesis, a prion is a misfolded form of a normal brain protein It can then convert a normal protein into the prion version, creating a chain reaction that increases their numbers

73 Laboratorium techniek Bacteria l The short generation span of bacteria helps them adapt to changing environments Genetic recombination produces new bacterial strains The control of gene expression enables individual bacteria to adjust their metabolism to environmental change Bacteria are haploid: mutations are immediately expressed

74 Laboratorium techniek Bacteria ll The major component of the bacterial genome is one double-stranded, circular DNA molecule –For E. coli, the chromosomal DNA consists of about 4.6 million nucleotide pairs with about 4,300 genes. –This is 100 times more DNA than in a typical virus and 1,000 times less than in a typical eukaryote cell –Tight coiling of the DNA results in a dense region of DNA, called the nucleoid, not bounded by a membrane In addition, many bacteria have plasmids, much smaller circles of DNA –Each plasmid has only a small number of genes, from just a few to several dozen

75 Laboratorium techniek Replication Bacterial cells divide by binary fission This is preceded by replication of the bacterial chromosome from a single origin of replication: rolling circle model

76 Laboratorium techniek Replication Bacteria proliferate very rapidly in a favorable natural or laboratory environment –E. coli can divide every 20 minutes, producing a colony of 10 7 to 10 8 bacteria in as little as 12 hours –In the human colon, E. coli reproduces rapidly enough to replace the 2 x bacteria lost each day in feces Through binary fission, most of the bacteria in a colony are genetically identical to the parent cell –However, the spontaneous mutation rate of E. coli is 1 x mutations per gene per cell division –This will produce about 2,000 bacteria in the human colon that have a mutation in that gene per day –New mutations, though individually rare, can have a significant impact on genetic diversity –Individual bacteria that are genetically well equipped for the local environment outgrow less fit individuals

77 Laboratorium techniek Recombination Recombination is the combining of DNA from two individuals into a single genome  generates diversity Recombination occurs through three processes: –Transformation –Transduction –Conjugation

78 Laboratorium techniek Transformation l Transformation is the alteration of a bacterial cell’s genotype by the uptake of naked, foreign DNA from the surrounding environment Discovered by Griffith in 1928.

79 Laboratorium techniek Transformation ll Many bacterial species have surface proteins that are specialized for the uptake of naked DNA –These proteins recognize and transport only DNA from closely related bacterial species –While E. coli lacks this specialized mechanism, it can be induced to take up small pieces of DNA if cultured in a medium with a relatively high concentration of calcium ions –In biotechnology, this technique has been used to introduce foreign DNA into E. coli

80 Laboratorium techniek Transduction l

81 Laboratorium techniek Generalised transduction Transduction occurs when a phage carries bacterial genes from one host cell to another In generalised transduction, a small piece of the host cell’s degraded DNA is packaged within a capsid, rather than the phage genome –These proteins recognize and transport only DNA from closely related bacterial species –When this pages attaches to another bacterium, it will inject this foreign DNA into its new host –Some of this DNA can subsequently replace the homologous region of the second cell –This type of transduction transfers bacterial genes at random

82 Laboratorium techniek Specialised transduction Specialized transduction occurs via a temperate phage –When the prophage viral genome is excised from the chromosome, it sometimes takes with it a small region of adjacent bacterial DNA –These bacterial genes are injected along with the phage’s genome into the next host cell –Specialized transduction only transfers those genes near the prophage site on the bacterial chromosome Both generalized and specialized transduction use phage as a vector to transfer genes between bacteria

83 Laboratorium techniek Conjugation Conjugation transfers genetic material between two bacterial cells that are temporarily joined One cell (“male”) donates DNA and its “mate” (“female”) receives the genes A sex pilus from the male initially joins the two cells and creates a cytoplasmic bridge between cells “Maleness,” the ability to form a sex pilus and donate DNA, results from an F factor as a section of the bacterial chromosome or as a plasmid

84 Laboratorium techniek Plasmids Plasmids, including the F plasmid, are small, circular, self- replicating DNA molecules Episomes, like the F plasmid, can undergo reversible incorporation into the cell’s chromosome –Temperate viruses also qualify as episomes. Plasmids generally benefit the bacterial cell They usually have only a few genes that are not required for normal survival and reproduction –Plasmid genes are advantageous in stressful conditions –The F plasmid facilitates genetic recombination when environmental conditions no longer favor existing strains –Many plasmids carry antibiotic resistance

85 Laboratorium techniek Conjugation ll The F factor or its F plasmid consists of about 25 genes, most required for the production of sex pili –Cells with either the F factor or the F plasmid are called F + and they pass this condition to their offspring –Cells lacking either form of the F factor, are called F -, and they function as DNA recipients When an F + and F - cell meet, the F + cell passes a copy of the F plasmid to the F - cell, converting it into an F + cell

86 Laboratorium techniek Conjugation lll The plasmid form of the F factor can become integrated into the bacterial chromosome The resulting Hfr cell (high frequency of recombination) functions as a male during conjugation

87 Laboratorium techniek Conjugation l V The Hfr cell initiates DNA replication at a point on the F factor DNA and begins to transfer the DNA copy from that point to its F - partner In the partially diploid cell, the newly acquired DNA aligns with the homologous region of the F - chromosome Recombination exchanges segments of DNA

88 Laboratorium techniek R Plasmids In the 1950s, Japanese physicians began to notice that some bacterial strains had evolved antibiotic resistance –The genes conferring resistance are carried by plasmids, specifically the R plasmid (R for resistance) –Some of these genes code for enzymes that specifically destroy certain antibiotics, like tetracycline or ampicillin When a bacterial population is exposed to an antibiotic, individuals with the R plasmid will survive and increase in the overall population Because R plasmids also have genes that encode for sex pili, they can be transferred from one cell to another by conjugation

89 Laboratorium techniek Key terms capsid provirus transformation temperate virus prophage prion viral envelope retrovirus transduction plasmodesma(ta) bacteriophage (phage) reverse transcriptase conjugation nucleoid host range HIV F factor virion lytic cycle AIDS episome R plasmid virulent virus vaccine F plasmid lysogenic cycle

90 Laboratorium techniek 90 Osmosis Water potential =R.T.i.M.10 –3 Mpa  total =  pressure +  solutes

91 Laboratorium techniek 91 Koch’s postulates 1.The microorganism should be shown to be present in all cases of animals suffering from a specific disease but shold not be found in healthy animals 2.The specific microorganism should be isolated from the diseased animal and grown in pure culture on artificial laboratory media 3. This freshly isolated microorganism, when inoculated into a healthy laboratory animal, should cause the same disease seen in the original animal 4. The microorganism should be reisolated in pure culture from the experimental infection

92 Laboratorium techniek 92 the  2 -statistic

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