Ch.20 Sexual Reproduction, Meiosis, Genetic Recombination

-use mitosis -progeny are identical to parent cells -does not involve fertilization -little/no genetic diversity -useful when env does not change

-involves meiosis & fertilization -brings together chromosomes from 2 diff parents to generate unique offspring -generates genetic diversity very quickly- every generation

-No genetic process generates diversity more quickly than sexual reproduction -Limited to genetic variation present in individuals of species due to rare occurence or mutations.

Even more rare-but advantageous to preserve in population, esp. in various combinations

-Haploid (1 copy of chromo.) cells or org's alternate w/diploid (2 copies of chromo. (homologous)) cells or org's -org's vary in prominence of haploid/diploid phases in life cycle

(eggs and sperm) contain half the complement of chromo. found in other cells produced by gametogenesis

fertilization or syngamy -the zygote, which contains two copies of each chromo (3 types of sexual life cycles)

-2 successie divisions, but only 1 DNA replication

(reduction division) -separates the 2 versions of each chromo. -Synapsis-pairing of homologous chromo during prophase I -Genetic recombo- exchange of genetic material during prophase I (crossing over)

(separation division) -separates the 2 sister chromatids (from DNA replication) of each chromo into daughter cells

-It halves the number of chromo- diploid parent cell results in haploid daughter cells

.....

DNA replicates, centrosome with centriols replicate, cell prepares for divison

....

Early Prophase I Dna condenses into chromosomes Nuclear envelope breaks down Mid Prophase I Mitotic spindle forms (kinetechore MT/fibers, polar MT, astral MT) Centrosomes migrate to opp cell poles Synapsis of homologous chromosomes Late Prophase I Crossing over-exchange genetic material occurs