BIOL 1000 Chapter Notes - Chapter 9 : Zygote, Transposable Element, Nuclear Membrane
29 Jun 2018
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Chapter 9: Genetic Recombination
9.1 Mechanism of Genetic Recombination
Genetic recombination: requires 2 DNA molecules that are different
from each other. It’s a mechanism for bringing them into close proximity & a
collection of enzymes to cut, exchange, & paste DNA back together (both DNA
backbones from each molecule).
Homology: allows DNA on diff. molecules to line up & recombine
precisely.
9.2 Genetic Recombination in Bacteria
Lederberg & Tatum: mutated bacteria to create strains that were different
in their ability to manufacture certain AAs and vitamins.
In bacteria, DNA of its chromosome may recombine with DNA brought
into close proximity of another cell. 3 primary mechanisms for bringing DNA
into bacteria from outside:
1) Conjugation: 2 cells form cytoplasmic bridge allowing DNA to move into
other cell from one; donated DNA can recombine with homologous sequences of
recipient. E.coli that’s DNA donor has F factor (part of main chromosome),
making them F+ while recipients have no factor and are F-. Genes from main
chrom. can go into F- cells
2) Transformation: intact cells of some species absorb pieces of DNA
released from disintegrated cells. Entering DNA fragments can recombine with
recipient’s DNA.
3) Transduction: DNA is transferred from one cell to another “by mistake”
inside head of an infecting virus bacteriophages. Generalized transduction
has all donor genes equally likely to be transferred is associated with virulent
bacteriophages in lytic cycle (kill host cells during each cycle of infection).
Specialized transduction associated with lysogenic cycle (DNA of bacteriophage
enters host & remains for generations)
9.3 Genetic Recombination in Eukaryotes: Meiosis
Animals have diploid (2n) life cycle in which diploid phase is
multicellular & haploid is unicellular. Meiosis is followed by gamete formation.
Products of meiosis are haploid gametes, & when one gamete fuses with another
(fertilization) diploid phase restored.
Plants & some fungi have alternating-generations life cycle in which
either haploid or diploid phases are multicellular & both divide by mitosis.
Diploid sporophytes are produced by fertilization, while haploid gametophytes
are produced by mitotic divisions of spores formed by meiosis.
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Document Summary
Genetic recombination: requires 2 dna molecules that are different from each other. It"s a mechanism for bringing them into close proximity & a collection of enzymes to cut, exchange, & paste dna back together (both dna backbones from each molecule). Homology: allows dna on diff. molecules to line up & recombine precisely. Lederberg & tatum: mutated bacteria to create strains that were different in their ability to manufacture certain aas and vitamins. In bacteria, dna of its chromosome may recombine with dna brought into close proximity of another cell. 3 primary mechanisms for bringing dna into bacteria from outside: Conjugation: 2 cells form cytoplasmic bridge allowing dna to move into. 1) other cell from one; donated dna can recombine with homologous sequences of recipient. E. coli that"s dna donor has f factor (part of main chromosome), making them f+ while recipients have no factor and are f-. Genes from main chrom. can go into f- cells.
