Chapter 8 Chromosome Variation Major types of chromosome mutations o Extra Genes Chromosome rearrangement Duplication FISH Fluorescent in situ hybridization used to label genes telomeres etc 1 of genes undergo duplication every million years A segment of the chromosome is duplicated Deletion A segment of the chromosome is deleted Translocation A segment of a chromosome moves from one chromosome Inversion A segment of the chromosome is turned 180 degrees to a nonhomologous chromosome or to another place on the same chromosome Drosophila have giant polytene chromosomes Meaning they have many copies of the same chromosome o Extra Chromosomes Aneuploidy Trisomy o Extra Set Polyploidy Autotriploid Developmental consequences of duplications deletions o Change in gene dosage o Over or under expression of genes o Imbalance in gene expression relative to other genes in the organism Developmental consequences of inversions translocations o Change in local gene environment o Differences in chromatin structure o May alter gene expression o Developmental abnormalities Structural consequences of inversions o Change in gene order disrupts pairing in meiosis o Leads to production of defective gametes sterility Para centric Inversion o Para means alongside beside PARAllel Next to centromere o Inversions DO NOT include the centromere o In Prophase 1 of Meiosis the chromosomes form an inversion loop 1 The Heterozygote possesses one wild type chromosome 2 And one chromosome with a paracentric inversion 3 In prophase 1 an inversion loop forms 4 A single cross over within the inverted region 5 The crossover within the inversion results in an unusual structure 6 One of the four chromatids now has two centromeres 7 And one lacks a centromere 8 In Anaphase 1 the centromeres separate stretch the dicentric chromatid which breaks The chromosome lacking the centromere is lost 9 Two gametes contain wild type nonrecombinant chromosomes 10 The other two contain recombinant chromosomes that are missing some genes The resulting recombinant gametes are nonviable because they are missing some these gametes will not produce viable offspring genes Peri centric inversions 6 The chromosomes separate in anaphase 1 7 The chromatids separate in anaphase II forming 4 gametes 8 Recombinant gametes are nonviable because genes are either missing or present in too many copies Translocations Arms of chromosomes replace one another often creating one larger chromosome and one fragment that is often lost o Peri Means around about PERImeter Enclosing the centromere o Inversions DO include the centromere 1 The heterozygote possesses one wild type chromosome 2 And one chromosome with a pericentric 3 4 inversion In prophase 1 an inversion loop forms If crossing over takes place within the inverted region 5 Two of the resulting chromatids have too many copies of genes and no copies of others o Change in local gene environments o Differences in chromatin structure o May alter gene expression o Complex translocation heterozygotes in Oenothera A crosslike configuration between the four chromosomes forms during prophase 1 of meiosis In anaphase 1 the chromosomes can separate in three different ways Alternate segregation Adjacent 1 segregation Adjacent 2 segregation rare When separated again in anaphase II to make 8 gametes only the alternatively segregated gametes are viable Polyploid crop plants include o Autopolyploids haploid sets derived from same species Potato 4n 48 chromosomes Banana 3n o Allopolyploids haploid sets derived from dif Species Cotton 4n 52 chromosomes Wheat 6n 42 chromosomes Auto polyploidy can occur by non disjunction in meiosis 1 o Triploids are usually partially sterile o Triploid grass carp are heat shocked to create sterile fish to control vegetation Allopolyploids can be produced by hybridization Meiotic gynogen Heat shocked eggs to suppress meiosis II Mitotic Gynogen Cold shocked to suppress mitosis Gynogenesis Cloning fish Development of embryo without fusion of the egg and sperm nuclei so that it only has maternal chromosomes Chapter 9 Bacterial and Viral Genetic Systems Bacteria often contain plasmids extrachromosal genetic elements Benefits of using E Coli in genetic research include o Small size and small genome o Rapid reproduction dividing every 20 minutes o Easy to culture in liquid medium or on petri plates o Many mutants available o 1 big circular chromosome with 4 64 million bp A bacteria colony that grows only on the supplemented medium with leucine has a mutation in a gene that encodes the synthesis of an essential nutrient GENETIC EXCHANGE IN BACTERIA o Prototrophic bacterial strains are created from two auxotrophic possesses a nutritional mutation disrupting its ability to synthesize an essential biological molecule strains to allow for nutrient synthesis 1 Transformation a Naked DNA is taken up by cell crossover in bacterium leads to the creation of a recombinant chromosome b The rate of cotransformation is inversely c proportional to the distances map distance between genes Inefficient Most cells do not take up DNA so electroporation is commonly used to increase the efficiency of transformation in competent cells 2 Conjugation a Cytoplasmic bridge forms between cells Transferred DNA is replicated then crossed over into the recipient cell to create a recombinant chromosome b Genetic exchange requires direct contact between bacterial cells Lederberg and Tatum s U tube with filter c F plasmid transfer i F cell donates a single strand of DNA replicates in the recipient bacteria and a double stranded copy of F plasmid resides in the recipient cell ii F Factor Episome of E Coli that controls conjugation and gene exchange between E Coli cells The F factor contains an origin of replication and genes that enable the bacteria to undergo replication F F F Hfr d High frequency recombinants Hfr cells i Crossing over takes place between F factor and chromosome integrating the F factor into it ii Crossing over may lead to recombination of alleles iii Transfer times can be recorded in regular intervals to map the genes on a replicating bacteria and can thus construct a genetic map 3 Transduction Exchange of genes transferred by phage particles a Davis U tube experiment that yielded genetic exchange showed that conjugation was not the mechanism but it was a phage transfer b Phage Life cycle i Lytic Cycle Replication of phage DNA by taking over host cell ii Lysogenic Cycle Phage DNA integrates into bacterial