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GENETIC RECOMBINATION Homologous chromosomes may carry different alleles for any given gene. In meiosis I, homologues pair and then segregate to different daughter cells The alignment of one homologous pair is independent of the other homologous pair during metaphase, therefore two possible combinations. Recombination occurs during meiosis I, more specifically prophase I. REQUIRES GETTING DNA FROM DIFFERENT CELLS INTO CLOSE PROXIMITY. Occurs when homologous haploid parental genomes are brought into close proximity with each other. The recombination is caused by the cutting, pasting, and exchanging of DNA molecules (repair of DNA in a way), yielding cells with different DNA sequence that those carried by either parent. ALL CHROMATIDS PAIR, NOT JUST THE INSIDE ONES! 3-D STRUCTURE, NOT 2-D! The independent alignment of recombined chromosomes in meiosis II results in many different combinations. The random fertilization of gametes (n) results in several possible zygotes (2n). Virtually only in animals is the haploid a gamete. Most time spent in mitosis rather than meiosis, diploid is multicellular. In most plants and fungi, spores are the haploid, rather than gametes. In some fungi and in algae, the haploid are multicellular, while the diploid are unicellular. Binary fission is an asexual process, and is used by bacteria to reproduce. The transfer of the F Factor involves an F+ donor, and a F- recipient, where the F plasmid is reproduced by “rolling” while transferring into the F- recipient. Bacterial genes can be transferred in a way similar to recombination, in that bridges are built between two circular chromosomes, and they simply “roll” to form a combined chromosome. This is known as integration. Conjugation or the movement from one cell into another cell of chromosomes, the remnant chromosomes from the donor cell become degraded after conjugation is finished. MENDELLIAN GENETICS T4 Phage involves a virus attaching to a cell, whose restriction enzymes are unable to stop infections, resulting in the host’s chromosomes being cut up. T4 phage chromosomes now in cell and start multiplying, and begin being given out to other T4 phage “bodies”, thus allowing them to multiply and continue spreading. The lytic cycle is how a virus develops and how the virus is spread. Transduction is the movement of DNA from one cell to another through the life cycle of a virus; it can then be recombinated into the chromosome, which will help promote resistance to the virus. Transformation is the natural ability of a cell to take up DNA from its environment. The typical Mendelian ratios (3:1, 1:2:1, 9:3:3:1) are only seen if the traits show complete dominance, have only two alleles, are coded by only one gene, are unaffected by the environment, and are carried on autosomes (non-sex chromosomes). Principle of Independent Assortment is the principle that the alleles of the genes that govern two
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This note was uploaded on 04/04/2009 for the course BIOLOGY 1222 taught by Professor Haffie during the Spring '09 term at UWO.

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