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Cell Division

process by which cell replicates DNA, doubles organelles and cytoplasm => splits into two daughter cell

identical = same genetic complement

cell division of prokaryotes (unicell) and eukaryote (unicell)

mech for reproduction

cell division of eukaryotes (multicell)

mech for reproduction and also replaces cells that are ready to retire

prokaryotes cell division

divide via binary fission

single DNA molecules attaches to cell membrane => duplicate and cell grows => cell membrane invaginates or pinches inward => two identical daughter cells

binary fission

type of asexual reproduction

eukaryotic cell division

multiple chromosomes per cell => segregate during duplication

make new cytoplasm and organelles


euk, contain diploid (2n) number of chromosomes

reproduce by cell cycle


germ cells, n number of chromosomes, 23 chromosomes from each parent

cell cycle phases

G1, S, G2, M

M = cells actually divide
other phases known as interphase


longest part of cell cycle (90%)

cells that enter terminal (muscle and nerve) => spend time in offshoot of G1 called G0

indie chromosomes not visible w/ light microscopy; as chromatin; DNA must be open so can transcribe genes from it an replicate prior to cell division

interphase parts

g1, S, g2

g1 stage (presynaptic gap)

create organelles for energy and protein production (mito, ribo, ER)

passage into S (syn) phase governed by restriction point; certain criteria

restriction point

passage into S (syn) phase governed by this, certain criteria, make sure all necessary equipment is available for S

S stage (synthesis)

cell replicates, or synthesizes, its genetic material so each daughter cell will have identical copies

after rep => each chromosome consists of two identical chromatids

duploidy of cell doesn't change, even though number of chromatids doubled (entering G2 contain twice as much as DNA) (46 chromosome, 92 chromatids)


form during S phase, each chromosome consist of two identical ones

bound together at centromere


two identical chromatids bound together at this specialized region

g2 stage (postsynthetic gap)

final stage before actual cell division

make sure enough organelles and cytoplasm to make 2 daughter cells

M stage

mitosis + cytokinesis

4 phases

DNA tightly bound into chromosomes => don't lose any material during division

4 phases of mitosis

prophase, metaphase, anaphase, telophase


splitting of cytoplasm and organelles into daughter cells


less condensed from of chromosomes

in interphase

centrioles (M stage)

proper movement of our chromosomes depend on specialized subcellular organelles

paired cylindrical organelles located as centrosome

during prophase => centrioles migration opp. poles of cell and being to form spindle fibers

centrosome (M stage)

paired cylindrical organelles located outside the nucleus in this region

spindle fibers (M stage)

made from microtubules

during prophase => centrioles migration opp. poles of cell and being to form this

radiate outward from centrioles => chromosomes attachment point for later separation during anaphase

asters (M stage)

extend toward center of cell to form spindle apparatus => shortening of apparatus => separation of sister chromatids

spindle fiber radiate outward from centrioles => chromosomes attachment point for later separation during anaphase


cont. process


refer either to single chromatid or pair of chromatids attached at the centromere

each chromatid is composed of a complete, doublestrand


each is composed of a complete, doublestrand molecule of DNA

sister ones are identical copies of each other


chromosomes condense

centrioles separate => opposite poles of cell => spindle apparatus forms between them

nuclear membrane dissolves => allow spindle fibers enter nucleus, while nucleoli become less distinct or disappear

kinetochores, w/ attached kinetochore fibers, appear at chromosome centromere


centriole pairs at opposite poles of cell

kinetochore fibers interact w/ fibers of spindle appartus to align chromosomes at metaphase (eq. plate), which equidistant to two poles of spindle fibers


centromeres split so each chromatid has its own distinct centromere, allowing sister chromatid to separate (pulled towards opposite poles of cell by shortening of kinetochore fibers)

telomere are last part of chromatids to separate

telophase and cytokinesis

spindle apparatus disappears

nuclear membrane re-forms around each set of chromosomes

chromosomes uncoil => resuming their interphase form

each two new nuclei receive a complete copy of genome identical to original


separate cytoplasm and organelles => survive on own

each cell has finite number of divisions before programmed death (human somatic cells between 20 and 50)

asexual reproduction

production of offspring from genetic material of single parent

4 diff forms of asexual reproduction

binary fission, budding, regeneration, pathenogenesis

binary fission

simple form of reproduction in prokaryotes

circular chromosome attaches to cell wall => replicates while cell grows => plasma membrane and cell wall grow inward along midline => two equal daughter cells


add. plasmid DNA NOT binary fission

in some simple eukaryotic cells


equal replication followed by unequal cytokinesis

daughter cell gets DNA identical to her parent's but far less cytoplasm

daughter can immediately break off or stay attached to parent until grows to full size

several organisms like hydra and yeast (both euk)


entire body parts can be regrown

primarily in lower organisms; higher have more difficultly, primarily due to nerve damage.


an adult organism develops from unfertilized egg. (ex: insects produce males)

haploid since only one parent contribute genetic material

sexual reproduction

offspring are unique

parent contribute 1/2 of offspring's genetic material

gametes contribute to process (meiosis)


specialized sex cells that contribute to sex reproduction


gametes are produced through this process

yields 4 diff. haploid (n) gametes


cells that under meiosis

mitosis vs. meiosis

mitosis - genetic material duplicated

mito - two identical diploid (2n) daughter cells
meiosis - 4 diff. haploid (n) gametes


composed of one round of replication followed by two rounds of division

meiosis I

first division

results in homo chromosomes being separated => haploid daughter cells (reductional division)

reductional division

results in homo chromosomes being separated => haploid daughter cells

meiosis II

second division

similar to mitosis

results in separation of sister chromatids (equational division)

4 genetically unique haploid cells

not preceded by chromosomal replication

equational division

results in separation of sister chromatids

4 genetically unique haploid cells

prophase I

same as mitosis prophase 1 except when homologous chromosomes comes together and intertwine in process known as synapsis

synaptic pair of homo chromosomes contains four chromatids = tetrad

chromatids of homo chromsomes may break in point of synapsis (chiasma) => crossing over => sister chromatids not identical => genetic recombination can unlink linked genes => inc. variety of genetic combo via gametogenesis => genetic diversity => capable of species to evolve and adpat to changing environment


homologous chromosomes comes together and intertwine in process


chromatids of homo chromsomes may break in point of synapsis

crossing over

chromatids of homo chromsomes may break in point of synapsis (chiasma) => exchange equivalent pieces

metaphase i

homo pairs align at metaphase plate

each pair attaches to a separate spindle fiber by kinetochore

anaphase I

homo pairs separate and pull to opposite poles of cell (disjunction)

paternal and maternal chromosomes separate, either end up in either daughter cell => random cell (unique pool of alleles)


homo pairs separate and pull to opposite poles of cell

telophase I

nuclear membrane forms around each new nucleus

chromosome still consists of sister chromatids joined at centromere

46 chromatids per cell, 2 per chromosome

may be short rest period, or interkinesis where chromosome partially uncoil


prophase ii

centrioles opp. poles

spindle fibers form

metaphase ii

chromosome line metaphase plate

centromeres divide, separating chromosomes into pairs of sister chromatids

anaphase ii

sister chromatids pulled to opposite poles by spindle fibers

telophase ii

nuclear membrane forms around each new haploid nucleus => cytokinesis follows => two daughter cells => 4 haploid daughter cells produced per gametocyte

females = onlry one of becomes functional gamete.


during anaphase i or II, homo or sister chromatids fail to separate =. one of gametes will have 2 copies of a particular chromosome and other gamete will have none => fertilization => zygote may have one too many or two few copies of chromosome

can affect both autosomal and sex chromosome


haploid sperm and ovum fuse during fertilization to form a single-celled this in fallopian tubes

fallopian tubes

zygote forms here


where sperm and ovum are produced, which in both males and females are derived from same embryological structure


primitive gonads developed into this in males

located in scrotum

2 func. components of testes

1. seminiferous tubules
2. intestitial cells (cells of Leydig)

seminiferous tubules

sperm produced in this highly coiled seminiferous tububles, nourished by Sertoli cells

Sertoli cells

seminiferous tubules nourished by this

cells of Leydig

secrete testosterone and androgens


secreted by cells of Leydig


other male sex hormones

secreted by cells of Leydig


testes are located here

an external pouch that hangs below penis


maintains a temp 2 to 4 degrees lower than body => essential to proper sperm production

enzymes work at lower temp


as sperm mature, they go here => gain mobility in form of flagellum and then stored until ejaculation


maturation takes approx. 72 days from origin until ready for ejaculation

as passes through reproductive tract => mixed w/ seminal fluid

once male reaches maturity => approx. 3 million produced per day

survive for one to two days after ejaculation if environment (uterine) is suitable


sperm travel through ejaculatory duct => urethra => exit body through penis

in males

reproductive and urinary systems share a common pathway

seminal fluid

produced through a joint effort by seminal vesicles, prostate gland,and bulbourethral gland


combo of sperm and seminal fluid

seminal vesicles

along w/ prostate gland,and bulbourethral gland, seminal fluid is produced through this

contribute fructose to nourish sperm

prostrate gland

along w/ seminal fluid and bulbourethral gland, seminal fluid is produced through this

gives fluid mildly alkaline properties => survive relative acidity of female reproductive tract

enlarged => surrounds urethra => urinary freq. and urgency


formation of haploid sperm through meiosis

occurs in seminiferous tubules

creates 4 functional sperm for echo spermatogonium


diploid stem cells in makes known as this

in process of differentiation => replicate their genetic material an develop into diploid primary spermatocytes

primary spermatocytes

in process of differentiation => replicate their genetic material an develop into this diploid

secondary spermatocytes

first meiotic division of spermatogonia

undergo meiosis II to generate haploid spermatids


spermatids undergo maturation to become this

mature sperm

very compact

consists of:
1. head (contains genetic material)
-covered by acrosome

2. midpiece (generate energy from fructose for motility) (mito abundance of this)

3. tail (for motility)


each sperm head covered by this cap

derived from Golgi appparatus

necessary to penetrate ovum


acrosome necessary to penetrate this

female reproductive organs


have separate excretory and reproductive tracts


gonads in female reproductive organs

produce estrogen and progesterone

below digestive system in pelvic cavity

each consists of thousands of follices


each ovary consists of thousands of these

multilayered sacs that contain, nourish and protect immature ova.

Egg pathway (between puberty and menopause)

one egg per month released into peritoneal sac => fallopian tube/oviduct

peritoneal sac

lines the abdominal cavity

one egg per month released into here


egg arries from peritoneal sac, lined w/ cilia to usher it along

fallopian tubes

connected to muscular uterus


site of fetal development


lower end of uterus

connects to vaginal canal

vaginal canal

cervix connects to this

where sperm is deposited during intercourse


passageway through which childbirth occurs


external female anatomy known as this


product of female gametes

female gametocytes meiotic process

no unending supply of stems cell => oogonia ever formed during fetal development

primary oocytes

at birth, females have this predifferentiated cells

2n (like primary spermatocytes), frozen in prophase I

secondary oocyte

once reaches menarche, one primary oocyte per month will complete meiosis I, producing this and a polar body

division characterized by unequal cytokinesis => ample cytoplasm to one daughter (secondary) and none to other (polar)

polar doesn't divide further or produce functional gametes.

remains frozen in metaphase II and doesn't complete remainder of meiosis II, unless fertilization occurs

capable of being fertilized w/in 24 hours of ovulation


until this, women ovulate one secondary oocyte approx. every 28 days

after this, ovaries become less sensitive (neg. back)to their stimulating hormones (FSH and LH) => hormones shoot high since don't have estrogen and progesterone feedback (both which secreted by ovaries) => eventually atrophy


fusion of haploid cells (2ndary oocyte + sperm)

usually in widest part of fallopian tube => restore diploid chromosome number => zygote


sperm + 2ndary oocyte

restores diploid chromosome number

fusion of sperm and 2ndary oocyte

sperm cells secrete acrosomal enzymes => digest corona radiata => zona pellucida

first sperm direct contact w/ 2ndary oocyte's cell membrane => sperm forms acrosomal apparatus => sperm nucleus freely into ovum (no longer 2ndary oocyte) => ovum undergoes cortical reaction => Ca released cytoplasm => fertilization membrane

release of Ca also inc. metabolic rate of ovum and soon to be zygote

acrosomal apparatus

sperm forms this when first sperm direct contact w/ 2ndary oocyte's cell membrane

extends and penetrates the membrane

cortical reaction

ovum undergoes this after sperm nucleus freely into ovum (no longer 2ndary oocyte)

fertilization membrane

Ca released cytoplasm of ovum

impenetrable to other sperm (prevent multiple fertilization)

two types of multiple births

monozygotic (identical) and dizygotic (fraternal) twins

monozygotic (identical) twins

single zygote splits into two => genetic material is all the same

if division is incomplete => conjoined twins

share same genome and blood type

have identical genome since originate indeterminately cleaved cells of the same embryo

dizygotic (fraternal) twins

two eggs release in same cycle => may both be fertilized

each zygote will implant in uterine wall individually and develop a separate placenta, chorion, and amnion (although placentas may fuse if zygotes implant close to each other)

no more genetically similar than any other pair of siblings

pathway of sperm (SEVEN UP)

seminiferous tubules


vas deferens

ejaculatory duct





spermatogonia (2n) => 1 spermatocyte (2n) (meiosis I) => 2 spermatocyte (n) (meiosis II) => spermatids (n) => spermatozoa (n)


1 oocyte (meiosis I) => 2 oocyte (fertilization, meiosis II) => ovum

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