study_guide3 - Exam 3 Study Guide Linked genes genes on the...

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Exam 3 Study Guide Linked genes – genes on the same chromosome pair Linked genes violate independent assortment because they are not equally represented or chanced during meiosis. Cis arrangement – parental type is PT and pt, recombinant is Pt and pT Trans arrangement – parental type Pt and pT, recombinant is PT and pt 1 map unit=1% difference btwn 2 recombinant genes # of recombinants/ total offspring If genes are on same chrom and are 50 m.u. apart or more, they appear unlinked & show 50% recomb Parental types are produced from NO crossing over. Recombinant types occur in crossing over in the parent during meiosis. The genetic map gives gene pair and % recombinance and you can then determine where each gene is in relation to each other. Prokaryotic Genetics Division by binary fission - The fission process begins when the DNA of the mother cell is replicated and joins into a circular structure, pair by pair; each circular DNA strand then attaches to the plasma membrane. Near the site of attachment, the cell elongates and causes the two duplicated chromosomes to separate. At this point, the plasma membrane pinches inward toward the middle of the cell; when it reaches the middle, the cell splits into two daughter cells. They are clones. Under perfect conditions, may replicate every 20 minutes. Genes are within 1 double-stranded circular chromosome. Differences may arise via mutation or recombination. Plasmids contain: non essential genes like resistance genes, conjugation genes (F factor) or genes that make the bacterium pathogenic. The F factor allows for gene conjugation. F+ strain – the F factor is NO T integrated in chromosome and is transferred with the plasmid during conjugation. An F- type becomes an F+ type this way. Hfr strain – F factor is integrates itself into the chromosome. F- type doesn’t become F+ because entire F factor isn’t transferred. This method allows for transfer of chromosomal genes. In conjugation experiments, Hfr used b/c they are non-resistant b/c don’t transfer plasmids w/ resis just F factors. Types of Recombination: Genes % A-B 20 B-C 5 A-D 30 C-D 45 B-D 50
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Conjugation – the direct transfer of DNA from one cell to another Transduction – transfer of DNA fro one cell to another via a viral intermediary. Transformation – the alteration of the genome by the uptake of extracellular DNA. Crossing over occurs and it’s own version of the gene leaves the cell. Temperate phages – can go through both lytic and lysogenic cycles. Lytic cycle – immediate release of progeny after infection. Lysogenic cycle – incorporation into host cell chromosome and induced when cell experiences unfavorable growth conditions. Prophage – a phage that is in the lysogenic stage. Generalized transduction – occurs when the bacterial chrom DNA fragment is packaged into phage head instead of viral DNA. It is a mistake in the LYTIC cycle. This fragment is introduced to recipient cell and can replace original DNA.
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