biol 1406 chapter 11

diploid cells

somatic (nonreproductive) cells of adults have 2 sets of chromosomes

haploid cells

gametes (eggs and sperm) have only 1 set of chromosomes

sexual reproduction

involves an alternation of meiosis (diploid → haploid) and fertilization (haploid → diploid)

germ-line cells

the diploid cells that undergo meiosis to produce haploid gametes

meiosis 1

separates homologous chromosomes, resulting in 2 haploid cells

meiosis 2

separates sister chromatids, resulting in 4 unique haploid cells, resembles a miotic division

synapsis

the pairing of homologous chromosomes during prophase 1, forming a structure called a bivalent or tetrad

synaptonemal complex

a protein structure that holds homologous chromosomes together during synapsis and facilitates crossing over

prophase 1

chromosomes condense, synapsis occurs, and crossing over takes place

crossing over (genetic recombination)

the exchange of genetic material between non-sister chromatids, producing genetic recombination

chiasmata

sites of crossing over, chromatids that remain connected after recombination

metaphase 1

homologous chromosome pairs align at the metaphase plate, orientation is random

anaphase 1

chiasmata break, homologous chromosomes separate, but sister chromatids remain attached at centromeres, independent assortment of maternal and paternal chromosomes

telophase 1

nuclear envelopes reform, and two haploid cells result (with sister chromatids still joined)

reduction division

another name for meiosis 1 because it reduces the number of chromosomes by half, converting a diploid cell (2n) into two haploid cells (n)

prophase 2

nuclear envelopes dissolve and new spindle apparatus forms

metaphase 2

chromosomes align on metaphase plate

anaphase 2

sister chromatids are separated from each other and move to opposite poles

telophase 2

nuclear envelope reforms around 4 sets of daughter chromosomes; cytokinesis follows

nondisjunction

failure of chromosomes to move to opposite poles during either meiotic division

aneuploid gametes

gametes with missing or extra chromosomes, result of nondisjunction events, most common cause of spontaneous abortion in humans

four distinct features of meiosis

homologous pairing and crossing over, sister chromatids remain joined at their centromeres and segregate together during anaphase 1, kinetochores of sister chromatids attach to the same pole in meiosis 1, DNA replication is suppressed between meiosis 1 and meiosis 2

shugoshin

protein that protects cohesion from separase-mediated cleavage during meiosis 1

features of mitosis

purpose: growth, repair, sexual reproduction

location: somatic (body) cells

number of divisions: 1

number of daughter cells: 2

chromosome number in daughter cells: diploid (2n) same as parent cell

genetic variation: no variation; identical to parent

crossing over: does not occur

homologous chromosomes: do not pair up

daughter cell identical to parent: yes

features of meiosis

purpose: sexual reproduction, gamete (sperm/egg) formation

location: germ cells (testes and ovaries)

number of divisions: 2

number of daughter cells: 4

chromosome number in daughter cells: haploid (n) half the parent cell

genetic variation: increases due to crossing over and independent assortment

crossing over: occurs during prophase 1

homologous chromosomes: pair up (synapsis) during prophase 1

daughter cell identical to parent: no (genetically unique cells)