Reproduction Flashcards
diploid
2n
contain two copies of each chromosome
i.e. autosomal cells
haploid
n
contain only one copy of each chromosome
i.e. germ cells
cell cycle
specific series of phases during which a cell grows, synthesizes DNA, and divides
derangements can lead to unchecked cell division and may be responsible for the formation of cancer
four stages: G1, S, G2, M
interphase
G1, S, G2 collectively
longest part of the cell cycle
chromatin
G0 stage
cell is simply living and serving its function, without any preparation for division
chromatin
less condensed form of chromosomes
allows for DNA to be available to RNA polymerase so genes can be transcribed
G1 stage
cells create organelles for energy and protein production (mitochondria, ribosomes, and ER), while also increasing size
restriction point
governs passage into S (synthesis) stage
criteria (i.e. containing the proper complement of DNA) must be met
S stage
cell replicates its genetic material so that each daughter cell will have identical copies
after replication, each chromosome consists of two identical chromatids bound together at specialized region known as centromere
G2 stage
cell phases through another quality checkpoint
DNA already duplicated
cell checks to ensure that there are enough organelles and cytoplasm to divide between two daughter cells
makes sure DNA replication proceeded correctly to avoid passing on error to daughter cells that may further replicate error to progeny
M stage
consists of mitosis itself along with cytokinesis
divided into four phases: prophase, metaphase, anaphase, telophase
p53
main protein in control of checking at restriction point (between G1/S) as well as at G2/M checkpoint to ensure that there is no damage to the DNA and that the cell has achieved adequate size and organelles have been properly replicated to support two daughter cells
cyclin-dependent kinases (CDK)
responsible for the cell cycle
require presence of right cyclins
conc’s of various cyclins increase/decrease during specific stages
cyclins bind to these creating an activated complex, which can then phosphorylate transcription factors
transcription factors
promote transcription of genes required for the next stage of the cell cycle
cancer
results when cell cycle control becomes deranged and damaged cells are allowed to undergo mitosis
one of the most common mutations found is of gene that produces p53 (TP53)
- cell cycle is not stopped to repair damaged DNA which allows for mutations to accumulate
tumors
created when cancer cells undergo rapid cell division
metastasis
if cancer cell begins to produce the right factors, the damaged cells are then able to reach other tissues
distant spread of cancerous cells through the bloodstream or lymphatic systems
mitosis
process by which two identical daughter cells are created from a single cell
four phases: prophase, metaphase, anaphase, telophase
occurs in somatic cells–cells not involved in sexual reproduction
finite number of divisions before programmed death: 20-50 for human somatic cells
prophase
first phase in mitosis
condensation of the chromatin into chromosomes
centriole pairs separate and move toward opposite poles of the cell
centrioles form spindle fibers made of microtubules, which radiate outward
nuclear membrane dissolves, allowing spindle fibers to contact the chromosomes
nucleoli become less distinct, may disappear completely
kinetochores appear at the centromere
centriole pairs
cylindrical organelles located outside the nucleus in centrosome region
responsible for the correct division of DNA
asters
formed from microtubules
anchor the centrioles to the cell membrane
kinetochores
protein structures located on the centromeres that serve as attachment points for specific fibers of the spindle apparatus
metaphase
centriole pairs are now at opposite ends of the cell
kinetochore fibers interact with the fibers of the spindle apparatus to align chromosomes at the metaphase plate
metaphase plate
equatorial plate
equidistant between the two poles of the cell
anaphase
centromeres split so that each chromatid has its own distinct centromere, allowing sister chromatids to separate
pulled toward the opposite poles of the cell by the shortening of the kinetochore fibers
telophase
reverse of prophase
spindle apparatus disappears
nuclear membrane reforms around each set of chromosomes and nucleoli reappear
chromosomes uncoil, resuming interphase form
each of two new nuclei has received a complete copy of the genome identical to the original genome and to each other
cytokinesis
cytokinesis
separation of the cytoplasm and organelles so that each daughter cell has sufficient supplies to survive on its own
gametocytes
germ cells in which meiosis occurs
results in up to four nonidentical sex cells
gametes
nonidentical sex cells
meiosis
occurs in germ cells to create four nonidentical sex cells (games
consists of one round of replication followed by two rounds of division
meiosis I
results in homologous chromosomes being separated, generating haploid daughter cells
reductional division
meiosis II
similar to mitosis
results in separation of sister chromatids
equational division
homologous pairs
considered separate chromosomes
human genome consists of 23
each contains one chromosome inherited from each parent
prophase I
meiosis I
chromatin condenses into chromosomes, spindle apparatus forms, nucleoli and nuclear membrane disappear
homologous chromosomes come together and intertwine in synapsis
crossing over occurs
tetrad
each chromosome consists of two sister chromatids, so each synaptic pair contains four chromatids
chiasma (pl. chiasmata)
point of synapsis
crossing over
chromatids of homologous chromosomes may break at point of synapsis and exchange equivalent pieces of DNA
occurs between homologous chromosomes and not between sister chromatids of the same chromosomes
genetic recombination, can unlink linked genes, thereby increasing the variety of genetic combinations that can be produced via gametogenesis
each daughter cell will have a unique pool of alleles from a random mixture of maternal and paternal origin
Mendel’s second law (of independent assortment)
inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes
metaphase I
meiosis I homologous pairs (tetrads) align at the metaphase plate and each pair attaches to a separate spindle fiber by its kinetochore (only ONE spindle fiber per pair of sister chromatids)
anaphase I
meiosis I
homologous pairs separate and are pulled to opposite poles of the cell
disjunction
accounts of Mendel’s first law (of segregation)
each chromosome of paternal origin separates from its homologue of maternal origin and either chromosome can end up in either daughter
segregation
separating of the two homologous chromosomes
distribution to the two intermediate daughter cells is random with respect to parental origin
telophase I
meiosis I
nuclear membrane forms around each new nucleus
each chromosome still consists of two sister chromatids joined at the centromere
cells are now haploid; once homologous chromosomes separate, only n chromosomes are found in each daughter cell (23 in humans)
cell divides into two daughter cells by cytokinesis
interkinesis
between cell divisions, there may be a short rest period during which the chromosomes partially uncoil
meiosis II
very similar to mitosis in that sister chromatids, rather than homologues, are separated from each other
by completion, up to four haploid daughter cells produced per gametocyte (oogenesis an exception)
prophase II
meiosis II
nuclear envelope dissolves, nucleoli disappear, centrioles migrate to opposite poles, spindle apparatus begins to form
metaphase II
meiosis II
chromosomes line up on metaphase plate
anaphase II
meiosis II
centromeres divide, separating chromosomes into sister chromatids
pulled to opposite poles by spindle fibers
telophase II
meiosis II
nuclear membrane forms around each new nucleus
cytokinesis follows, and two daughter cells are formed
X chromosome
carries sizable amount of genetic information
sex-linked disorders
cause by mutations in genes of X chromosome
most are inherited recessively
females express them far less frequently than males
hemizygous
males with respect to many of the genes on the X chromosome because they only have one copy
carriers
females carrying a diseased allele on an X-chromosome, but not exhibiting the disease
Y chromosome
contains very little genetic information
in its absence, all zygotes will be female, but in its presence a zygote will be male
SRY (sex-determining region Y)
notable gene on Y chromosome
codes for a transcription factor that initiates testis differentiation and thus the formation of male gonads
testes
primitive gonads develop into these
have two functional components: seminiferous tubules and interstitial cells (of Leydig)
located in scrotum
sperm
produced in the highly coiled seminiferous tubules, nourished by Sertoli cells
testosterone
secreted by cells of Leydig, which also secrete other male sex hormones (androgens)
scrotum
external pouch that hangs below the penis and maintains a temperature 2˚ to 4˚C lower than the body
epididymis
where flagella of sperm gain motility
stored until ejaculation
ejaculation
sperm travel through the vas deferens to the ejaculatory duct at the posterior edge of the prostate gland
urethra
formed from the fusion of the two ejaculatory ducts, carries sperm through the penis as they exit the body (reproductive and urinary systems share a common pathway)
seminal fluid
mixed with sperm as they pass through the reproductive tract
produced through a combined effort by the seminal vesicles, prostate gland, and bulbourethral gland
seminal vesicles
combine fructose to nourish sperm, give the seminal fluid mildly alkaline properties so the sperm will be able to survive in the relative acidity of the female reproductive tract
prostate gland
gives the seminal fluid mildly alkaline properties so the sperm will be able to survive in the relative acidity of the female reproductive tract
bulbourethral (Cowper’s) glands
produce a clear viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal
semen
the combination of sperm and seminal fluid
spermatogenesis
formation of haploid sperm through meiosis
occurs in the seminiferous tubules
results in four functional sperm for each spermatogonium
spermatogonia
diploid stem cells in males
primary spermatocytes
after replicating their genetic material (S stage) spermatogonia develop into these
secondary spermatocytes
first meiotic division of primary spermatocytes, results in haploid cells
spermatids
secondary spermatocytes undergo meiosis II to generate these haploid cells
spermatozoa
after spermatids undergo maturation
midpiece
sperm
filled with mitochondria, which generate the energy to be used as the sperm swims through the female reproductive tract to reach the ovum in the fallopian tubes
acrosome
cap that covers each sperm head
derived from the Golgi apparatus and is necessary to penetrate the ovum
ovaries
female gonads
produce estrogen and progesterone
located in the pelvic cavity
each consists of thousands of follicles
follicles
multilayered sacs that contain, nourish, and protect immature ova (eggs)
peritoneal sac
lines the abdominal cavity
through which one egg per month is ovulated
fallopian tube (oviduct)
lined with cilia to propel the egg forward
connected to the uterus
uterus
muscular
site of fetal development
cervix
lower end of the uterus
connects to the vaginal canal
vaginal canal
where sperm are deposited during intercourse
also passageway through which childbirth occurs
vulva
external female anatomy known collectively
ovaries
female gonads
produce estrogen and progesterone
located in the pelvic cavity
each consists of thousands of follicles
follicles
multilayered sacs that contain, nourish, and protect immature ova (eggs)
primary oocytes
once oogonia undergo DNA replication (happens by birth)
cells are 2n and are arrested in prophase I
fallopian tube (oviduct)
lined with cilia to propel the egg forward
connected to the uterus
uterus
muscular
site of fetal development
cervix
lower end of the uterus
connects to the vaginal canal
vaginal canal
where sperm are deposited during intercourse
also passageway through which childbirth occurs
vulva
external female anatomy known collectively
oogenesis
production of female gametes
zygote
2n
produce upon completion of meiosis II where haploid pronuclei of the sperm and ovum join
primary oocytes
once oogonia undergo DNA replication (happens by birth)
menarche
first menstrual cycle
begins the process of one primary oocyte completing meiosis I per month
secondary oocyte
completion of meiosis I by primary oocyte produces this and a polar body
division characterized by unequal cytokinesis
remains arrested in metaphase II and does not complete the remainder of meiosis II unless fertilization occurs
polar body
gets very little cytokinesis at the end of meiosis I
generally does not divide further and will never produce functional gametes
zona pellucida
surrounds oocyte itself and is an acellular mixture of glycoproteins that protect the oocyte and contain compounds necessary for sperm cell binding
corona radiata
lies outside the zone pellucida and is a layer of cells that adhered to the oocyte during ovulation
estrogens
secreted in response to FSH
result in development and maintenance of the female reproductive system and female secondary sexual characteristics (breast growth, widening of the hips, changes in fat distribution)
in embryo, stimulate development of the reproductive tract
in adults, lead to thinking of lining of uterus each month in preparation for implantation of a zygote
zygote
2n
produce upon completion of meiosis II where haploid pronuclei of the sperm and ovum join
hypothalamus
prior to puberty, restricts production of GnRH
at start of puberty, restriction is lifted–releases pulses of GnRH
gonadotropin-releasing hormone (GnRH)
released by hypothalamus
triggers the anterior pituitary gland to synthesize and release FSH and LH
follicular phase
begins when menstrual flow begins
GnRH secretion from the hypothalamus increases in response to the decreased concentrations of estrogen and progesterone, which fall off toward the end of each cycle
higher concentrations of GnRH cause increased secretions of both FSH and LH
work in concert to develop several ovarian follicles
begin to produce estrogen, which has negative feedback effects and causes the GnRH, LH, and FSH concentrations level off
estrogen works to regrow the endometrial lining, stimulating vascularization and glandularization of the decidua
late in phase, developing follicles secrete higher and higher concentrations of estrogen
ovulation phase
estrogen concentrations reach a threshold that paradoxically results in positive feedback, and GnRH, LH, and FSH levels spike
surge in LH induces the release of the ovum from the ovary into the abdominal (peritoneal) cavity
testosterone
produced by the testes
dramatically increases during puberty, sperm production begins
not only develops and maintains the male reproductive system but also results in the development of secondary sexual characteristics
production remains high through adulthood and declines as men age
exerts negative feedback on hypothalamus and anterior pituitary so that production is limited to appropriate levels
secondary sexual characteristics
i.e. facial and axillary hair, deepening of voice, and changes in growth patterns
estrogens
secreted in response to FSH
result in development and maintenance of the female reproductive system and female secondary sexual characteristics (breast growth, widening of the hips, changes in fat distribution)
in embryo, stimulate development of the reproductive tract
in adults, lead to thinking of lining of uterus each month in preparation for implantation of a zygote
progesterone
secreted by the corpus luteum in response to LH
increasingly involved in the development and maintenance of the endometrium but not in initial thickening of the endometrium
corpus luteum
remnant follicle that remains after ovulation
secretes progesterone in response to LH
menstrual cycle
menarche to menopause
cyclic pattern of estrogen and progesterone levels rising and falling
in response, endometrial lining will grow and be shed
can be divided into four events: follicular phase, ovulation, the luteal phase, and menstruation
ovulation
estrogen concentrations reach a threshold that paradoxically results in positive feedback, and GnRH, LH, and FSH levels spike
surge in LH induces the release of the ovum from the ovary into the abdominal (peritoneal) cavity
luteal phase
after ovulation, LH causes ruptured follicle to form the corpus luteum with secretes progesterone
maintains uterine lining for implantation
progesterone levels begin to rise while estrogen levels remain high
high levels of progesterone again cause negative feedback on GnRH, FSH, and LH, preventing the ovulation of multiple eggs
menstruation phase
assuming that implantation does not occur, corpus luteum loses its stimulation from LH, progesterone levels decline, and the uterine lining is sloughed off
loss of high levels of estrogen and progesterone removes the block on GnRH so that the next cycle can begin
human chorionic gonadotropin (hCG)
if fertilization has occurred, resulting zygote will develop into a blastocyst that will implant in uterine lining and secrete this hormone
analog of LH, looks very similar chemically and can stimulate LH receptors
maintains corpus luteum
critical during first trimester development because it is the estrogen and progesterone secreted by the corpus luteum that keep the uterine lining in place
by second trimester, levels decline because placenta has grown to a sufficient size to secrete progesterone and estrogen by itself
menopause
as a woman ages, ovaries become less sensitive to FSH and LH, resulting in ovarian atrophy
as estrogen and progesterone levels drop, endometrium atrophies and menstruation stops
because negative feedback on FSH and LH is removed, blood levels of these rise
accompanied by profound physical and physiological changes (flushing, hot flashes, bloating, headaches, and irritability)
occurs between the ages of 45-55
luteal phase
after ovulation, LH causes ruptured follicle to form the corpus luteum with secretes progesterone
maintains uterine lining for implantation
progesterone levels begin to rise while estrogen levels remain high
high levels of progesterone again cause negative feedback on GnRH, FSH, and LH, preventing the ovulation of multiple eggs
menstruation phase
assuming that implantation does not occur, corpus luteum loses its stimulation from LH, progesterone levels decline, and the uterine lining is sloughed off
loss of high levels of estrogen and progesterone removes the block on GnRH so that the next cycle can begin
human chorionic gonadotropin (hCG)
if fertilization has occurred, resulting zygote will develop into a blastocyst that will implant in uterine lining and secrete this hormone
analog of LH, looks very similar chemically and can stimulate LH receptors
maintains corpus luteum
critical during first trimester development because it is the estrogen and progesterone secreted by the corpus luteum that keep the uterine lining in place
by second trimester, levels decline because placenta has grown to a sufficient size to secrete progesterone and estrogen by itself
menopause
as a woman ages, ovaries become less sensitive to FSH and LH, resulting in ovarian atrophy
as estrogen and progesterone levels drop, endometrium atrophies and menstruation stops
because negative feedback on FSH and LH is removed, blood levels of these rise
accompanied by profound physical and physiological changes (flushing, hot flashes, bloating, headaches, and irritability)
occurs between the ages of 45-55
