sexual reproduction I suppose

what is the main purpose of sexual reproduction

generate random assortment of chromosome combinations

why is meiosis necessary for sexual reproduction

reduces the number of chromosomes by half (reduction phase) (gametogenesis) (haploid)

what does fertilization do in meiosis

restores the chromosome number to normal

syngamy

fusion of two gametes to double the number of chromosomes

4 stages of meiosis

• interphase I: DNA replication to ready for division

• division I (meiosis 1): reduction division

• interphase II: resting phase with no DNA replication

• division II (meiosis 2): separates sister chromatids

prophase I: 4

• nuclear membrane disappears and centrioles divide and generate spindle fibers

• homologous chromosomes move in proximity to each other

• chromosomal pairs are attached to each other (synapsis)

• intertwined chromatids zip themselves together at points called chiasmata and exchange genetic info in crossing over

prophase I summary: 3

• crossing over (chiasma forms)

• nuclear membrane disappears

• nucleolus becomes invisible

metaphase I:

homologous chromosomes attach themselves to spindle fibers along the equatorial plate

anaphase I: 4

• chromosome pairs move to separate poles

• homologous pairs separate (segregation)

• sister chromatids remain attached and begin migrating up to poles

• in humans there are 23 double chromosomes at each pole

telophase I: 5

• secondary gametocytes formed

• cells have one homologous pairs, sister chromatids have not yet separated

• nuclear membrane forms around dyads of sister chromatids

• chromosomes DO NOT uncondense

• cytokinesis

interphase II: 5

• resting phase

• short

• chromosomes do not completely unwind

• NO DNA REPLICATION

• often skipped and straight to prophase II

prophase II:

nuclear membranes disappear, spindle fibers begin to form

metaphase II: 2

• dyads: (single chromosomes line up with two sister chromatids) line up and form on equitorial plate

• spindle fibers attach to centromeres

anaphase II: 2

• centromeres release and chromatids begin to separate

• chromatids migrate to the spindle poles (now considered a chromosome)

telophase II: 2

• cytokinesis and complete decondensation is completed forming 4 haploid cells called monads (each vary in structure)

• telophase I produced 2 daughter cells and therefore telophase II produces four granddaughter cells

what does gametogenesis do

makes female and male sex cells through meiosis

male sex cells through meiosis

symmetrical, producing four small sperm cells

female sex cells through meiosis

asymmetrical, producing one large egg cell and three polar bodies, thereby concentration cytoplasm to ensure viability of the egg

nondisjunction: 2

• when two homologous chromosomes move to the same pole during meiosis

• one daughter cells will be missing one chromosome (monosomy) and the other will have an extra chromosome (trisomy)

alternation of generations: 2

• cycling between diploid (2N) and haploid (N) stages within the life cycle of sexually reproducing plants and animals

• have bodies that survive in those environments, not only gametes

spore

haploid cells that germinates when conditions are right

what does a sporophyte (2n) produce

one or more haploid spores (n) through meiosis

if a spore developed without fertilization they will develop into…

…gametophytes (n) - a gamete (n) making body

how will the gametes create a new sporophyte

via fertilization and fuse to create (2n)

what is the advantage of switching between asexual and sexual reproduction

survive in different kinds of reactions and environments

advantage of sexual reproduction

opportunity for genetic variation which can aid in selective advantage in changing environments

advantage of asexual reproduction

tends to be quicker and thus can take advantage of a stable environment by increasing populations

fragmentation:

kind of asexual reproduction in animals when a limb plus a part of its center breaks off and can regenerate (is genetically identical to OG)

parthenogenesis

used by egg laying organisms if fertilization is not possible (eggs can still develop into mature adults)

mitosis vs meiosis what kind of cells are produced

• mitosis: body cells

• meiosis: sex cells

mitosis vs meiosis regarding homologous chromosomes

• mitosis: line up independently along equatorial plate during metaphase

• meiosis: line up together along equatorial plate forming a line of 4 similar chromatids during metaphase I

mitosis vs meiosis prophase

• mitosis: short prophase

• meiosis: long prophase

mitosis vs meiosis where does it happen

• mitosis: all locations of the body

• meiosis: only in gonads

mitosis vs meiosis when do chromosomes replicate

before both processes

mitosis vs meiosis what does each create

• mitosis: 2 daughter cells

• meiosis: 4 granddaughter cells

mitosis vs meiosis are their products capable of further division?

• mitosis: yes further mitotic division

• meiosis: no further meiotic division

mitosis vs meiosis are the daughter cells identical:

• mitosis: yes

• meiosis: no due to crossing over

mitosis vs meiosis what kind of cells does it result in?

• mitosis: diploid

• meiosis: haploid