Ch. 2: Reproduction Flashcards
defn + types of cells: diploid vs. haploid
DIPLOID = 2n = contain two copies of each chromosome
- autosomal cells
HAPLOID = n = only one copy of each chromosome
- germ cells
what is the cell cycle?
the series of phases that eukaryotic cells replicate through
what are the four stages of the cell cycle for actively dividing cells?
G1
S
G2
M
defn: interphase
the first three stages (G1, S, and G2)
the longest part of the cell cycle (actively dividinig cells spend 90% of their time here)
defn: G0 phase
an offshoot of G1
this is where cells that do not divide spend all of their time
the cell simply lives and carries out its functions, without any preparation for division
what form is DNA in during interphase? how does this affect visualization with light microscopy?
why is DNA in this form?
chromatin (less condensed form)
individual chromosomes are not visible with light microscopy in this state
it is in this form because DNA must be available to RNA polymerase so that genes can be transcribed
steps (2) + aka: G1 phase
Presynthetic gap
cells create organelles for energy and protein production (mitochondria, ribosomes, endoplasmic reticulum), while also increasing their size
what criterion must be met for the cell to pass from the G1 to S stage? what is this junction calle?
restriction point
criteria: containing the proper complement of DNA
steps (2) + aka: S stage
Synthesis of DNA
- cell replicates its genetic material so that each daughter cell will have identical copies
- after replication, each chromosome consists of two identical chromatids that are bound together at a specialized region (the centromere)
how many chromosomes are present after replication (after S stage)? what does this imply about the amount of DNA entering G2 as compared to G1?
still 46! 92 chromatids are present, but the ploidy has not changed
cells entering G2 have twice as much DNA as cells in G1
defn: chromatid vs. chromosome
CHROMATID = composed of a complete double-stranded molecule of DNA
- sister chromatids are identical copies of each other
CHROMOSOME = a single chromatid before S phase OR the pair of chromatids attached at the centromere AFTER the S phase
steps (3) + aka: G2 stage
postsynthetic gap
- cell passes through another quality control checkpoint
- DNA has already been duplicated, and the cell checks to make sure there are enough organelles and cytoplasm for two daughter cells
- the cell also checks to make sure the DNA proceeded correctly to avoid passing on an error to daughter cells
what are the two checkpoints that control the cell cycle?
G1/S and G2/M
what is the main point of the G1/S checkpoint?
what happens to the cell if there is damage at this checkpoint?
what is the main protein in control of this?
the cell determines if the condition of the DNA is good enough for synthesis
if there is DNA damage: the cell cycle goes into arrest until the DNA has been repaired
main protein: p53
what is the main point of the G2/M checkpoint?
what is the main protein?
the cell is mainly concerned with ensuring that it has achieved adequate size and the organelles have been properly replicated to support w daughter cells
main protein: p53
defn + how they work (4): cyclins and cyclin-dependent kinases (CDK)
the molecules responsible for the cell cycle
- to be activated, CDKs require the presence of the right cyclins
- during the cell cycle, concentrations of the different cyclins increase and decrease during specific stages
- these cyclins bind to CDKs, creating an activated CDK-cyclin comlex
- this complex can then phosphorylate transcription factors
defn: transcription factors
promote transcription of genes required for the next stage of the cell cycle
why is cell cycle control needed?
to ensure that cells that are damaged or inadequately sized do not divide
what happens when cell cycle control falters, and damaged cells undergo mitosis?
cancer may result!
defn + result (3): mutation of TP53
one of the most common mutations found in cancer
mutation of the gene that produces p53 (TP53)
when this is mutated
1. the cell cycle is not stopped to repair damaged DNA
2. mutations accumulate
3. results in a cancerous cell that divides continuously and without regard to the quality or quantity of the new cells produced
steps: tumors vs. metastasis vs. middle stage
TUMOR: cancer cells undergo rapid division
MIDDLE STAGE: eventually if the cell begins to make the right factors, the damaged cells are then able to reach other tissues
METASTASIS: may be local invasion as well as distant spread of cancerous cells through the bloodstream or lymphatic systems
defn: mitosis
the process by which 2 identical daughter cells are created from a single cell
what are the 4 phases of mitosis? + mnemonic
PMAT
Prophase
Metaphase
Anaphase
Telophase
what kind of cells does mitosis occur in?
somatic cells (cells not involved in sexual reproduction)
summarize the main accomplishments of the 4 phases of mitosis
PROPHASE - chromosomes condense, spindle forms
METAPHASE - chromosomes align
ANAPHASE - sister chromatids separate
TELOPHASE - new nuclear membranes form
what are the two microtubule organizing centrs of the cell?
- the centrosome
- the basal body of a flagellum or cilium
defn : cytokinesis
occurs at the end of telophase
separation of the cytoplasm and organelles (gives each daughter cell enough material to survive on its own)
can cells divide infinitely?
no; each cell undergoes a finite number of divisions before programmed death (for human somatic cells, that is usually 20 - 50)
what types of cells does meiosis occur in? what are the results of meiosis?
occurs in: germ cells (gametocytes)
results in: four nonidentical sex cells (gametes)
what are 3 similarities between mitosis and meiosis?
- genetic material must be duplicated
- chromatin is condensed to form chromosomes
- microtubules emanating from centrioles are involved in dividing genetic material
how many rounds of replication and division are there in mitosis and meiosis each?
Mitosis: 1 replication, 1 division
Meiosis: 1 replication, 2 division
what is the result of meiosis I? (aka?)
homologous chromosomes being separated –> generates haploid daughter cells
aka: reductional division
what is the result of meiosis II? aka?
results in the separation of sister chromatids without a change in ploidy
equational division
which is more similar to mitosis: meiosis I or meiosis II?
meiosis II
defn: homologous pairs vs. sister chromatids
HOMOLOGOUS PAIRS = considered separate chromosomes (i.e. maternal chromosome 15 and paternal chromosome 15)
SISTER CHROMATIDS = identical strands of DNA connected at the centromere
how many homologous pairs of chromosomes (homologues) is the human genome composed of?
23
after the S phase, how many chromatids, chromosomes, and homologous pairs are there?
92 chromatids
organized into
46 chromosomes
organized into
23 homologous pairs
each homologous pair contains one WHAT from each parent?
one chromosome
how is crossing over characterized?
by the number of crossover events that occur in one strand of DNA (single crossovers, double crossovers, etc.)
why does it logically make sense that crossing over occurs between homologous chromosomes and NOT between sister chromatids of the same chromosome?
the latter are identical, so crossing over would not produce any change
defn: recombination
the result of crossing over
the chromatids involved are left with an altered but structurally complete set of genes
what effect does genetic recombination have on linked genes?
it can unlink linked genes –> increases the variety of genetic combos that can be produced via gametogenesis
defn: linkage
the tendency for genes to be inherited together
how does physical distance between genes affect crossing over and linkage?
the FARTHER genes are located from each other the
LESS likely they are to be inherited together and are
MORE likely to undergo crossing over
what advantage does sexual reproduction provide that asexual reproduction doesnt?
great genetic diversity!! –> increased ability to evolve and adapt to a changing environment
defn: Mendel’s second law of independent assortment
the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes
what does each daughter cell have because of crossing over?
a unique pool of alleles from a random mixture of maternal and paternal origin
what part of anaphase I of meiosis I accounts for Mendel’s first law of segregation?
disjunction
defn: interkinesis
a short rest period that may occur between cell divisions during which the chromosomes partly uncolil
what are the 4 main differences between meiosis and mitosis?
Mitosis: 2n –> 2n
Meiosis: 2n –> n
Mitosis: occurs in all dividing cells
meiosis: occurs in sex cells only
mitosis: homologous chromosomes do not pair
meiosis: homologous chromosomes align on opposite sides of the metaphase plate
mitosis: no crossing over
meiosis: crossing over can occur
what is chromosomal sex determined by? what are the two types?
by the 23rd pair of chromosomes
XX: female
XY: male
what chromosomes do ova and sperm carry?
ova: X chromosome
sperm: either X or Y chromosome
mnemonic: X-linked mutations
SeX-linked is X-linked
defn: hemizygous
males are termed this with respect to many genes on the X chromosome because they only have one copy
char (4): X-linked disorders
- a male with a disease-causing allele on the unpaired part of the X chromosome will necessarily express that allele (hemizygous)
- females may be homozygous or heterozygous with respect to genes on the X chromosome
- most X-linked disorders are recessively inherited
- females express these disorders far less frequently than males
defn: carrier
a female carrying a diseased allele on an X chromosome but not exhibiting the disease
which contains more genetic information: the X or Y chromosome?
X!
defn + location + func: SRY
SRY = sex-determining region Y
one notable gene on the Y chromosome
codes for a transcription factor that initiates testis differentiation and thus the formation of male gonads
in Y chromosome absence: ALL zygotes female
in Y chromosome presence: zygote is male
mnemonic: pathway of sperm through the male reproductive system
SEVE(N) UP
Seminiferous tubules
Epididymis
Vas deferens
Ejaculatory duct
(Nothing)
Urethra
Penis
what do the primitive gonads in males develop into?
testes
what are the two functional components and what do they do + char?
- SEMINIFEROUS TUBULES = highly coiled
produces sperm - INTERSTITIAL CELLS OF LEYDIG = secrete testosterone and other male sex hormones (androgens)
func: Sertoli cells
nourishes seminiferous tubules
defn: scrotum
an external pouch that hangs below the penis and contains the testes
why and how (2) do the testes have a lower temperature than the rest of the body?
- there is a layer of muscle around the vas deferens that can raise and lower the testis to keep proper temperature
- the location of the testes below the penis
for proper sperm development
what happens to sperm in the epididymis?
their flagella gain motility
during ejaculation, what 2 parts of the male system does sperm travel through or to?
- vas deferens
- ejaculatory duct
func + what is it formed from: urethra
the two ejaculatory ducts fuse to form it
carries sperm through the penis as they exit the body
defn + 3 parts that produce it: seminal fluid
mixes with sperm as they pass through the reproductive tract
- seminal vesicles
- prostate gland
- bulbourethral gland
func: seminal vesicles
contribute fructose to nourish sperm
give the fluid mildly alkaline properties
func: prostate gland
gives the fluid mildly alkaline properties
why do the seminal vesicles and prostate gland give the sperm mildly alkaline properties?
so they can survive in the relative acidity of the female reproductive tract
func: bulbourethral (Cowper’s) glands
produce a clear viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal
defn: semen
the combination of sperm and seminal fluid
defn: spermatogenesis and spermatogonia
SPERMATOGENESIS = the formation of haploid sperm through meiosis (occurs in the seminiferous tubules)
SPERMATOGONIA = male diploid stem cells
what are the 5 steps of sperm development and what are they called at that stage?
- SPERMATOGONIA = male diploid stem cells
- diploid PRIMARY SPERMATOCYTES = after replicating their genetic material (S stage)
- haploid SECONDARY SPERMATOCYTES = after the first meiotic division
- haploid SPERMATIDS = after meiosis II
- SPERMATOZOA = after maturation
how many functional sperm are resulted from spermatogenesis per spermatogonium?
4!
what are the three main parts of mature sperm and what are their basic functions?
- HEAD = contains genetic material
- MIDPIECE = generates ATP from fructose
- FLAGELLUM = for motility
why is the midpiece of the sperm filled with mitochondria?
they generate the energy for swimming through the female reproductive tract to reach the ovum in the fallopian tubes
defn + func + origin: acrosome
defn: a cap that covers each sperm head
func: necessary to penetrate the ovum
origin: derived from the Golgi apparatus
defn + func: ovaries
gonads
produce estrogen and progesterone
defn + func: follicles
thousands of these are in the ovaries
multilayered sacs that contain, nourish, and protect immature ova (eggs)
how many eggs are ovulated a month and what is the path from ovary to exit?
1
- goes into the peritoneal sac (lines the abdominal cavity)
- then the fallopian tube (oviduct; lined with cilia to propel the egg forward)
- uterus
defn: oogenesis
the production of female gametes
gametocytes undergo the same meiotic process in both females and males, but what is a difference between them?
there is no unending supply of stem cells analogous to spermatogonia in females
defn + char: primary vs. secondary oocytes
PRIMARY OOCYTES
by birth, all oogonia have undergone DNA replication
these cells are 2n and are arrested in prophase I
SECONDARY OOCYTES
produce along with a polar body when one primary oocyte per month completes meiosis I
arrested in metaphase II, does not complete the rest of meiosis II unless fertilization occurs
polar body: does not divide further, will never produce functional gametes
why does a polar body get produced alongside a secondary oocyte?
because of unequal cytokinesis which distributes ample cytoplasm to one daughter cell (the secondary oocyte) and nearly none to the other (the polar body)
defn + func: zona pellucida ; corona radiata
the two layers that surround oocytes
ZONA PELLUCIDA
1. surrounds the oocyte itself
2. an acellular mixture of glycoproteins (protects the oocyte) and compounds needed for sperm binding
CORONA RADIATA
1. outside the zona pellucida
2. a layer of cells that adheres to the oocyte during ovulation
what triggers meiosis II of a secondary oocyte?
when a sperm cell penetrates the corona radiata and zona pellucida with the help of acrosomal enzymes
result: meiosis II of a secondary oocyte
splits into a mature ovum and another polar body
func + char: mature ovum
- a large cell consisting of large amts of cytoplasm and organelles
contributes nearly everything to the zygote (half of the DNA, all of the cytoplasm, organelles, and RNA for early cellular processes)
sperm contribute the other half
what happens upon completion of meiosis II?
the haploid pronuclei of the sperm and the ovum join, creating a diploid zygote
what is the status of production of gonadotropin-releasing hormone (GnRH) before and during puberty
PRE-PUBERTY: the hypothalamus restricts production of GnRH
START OF PUBERTY: this restriction is lifed as the hypothalamus releases pulses of GnRH
what is the immediate effect and secondary affect of the restriction on GnRH production being lifted at the start of puberty?
the anterior pituitary grand is triggered to synthesize and release follicle-stimulating hormone FSH and luteinizing hormone LH
these hormones trigger the production of other sex hormones that develop and maintain the reproductive symptom
what is the status of androgen production during the fetal period, and then during the duration of infancy and childhood?
FETAL PERIOD (from nine weeks after fertilization until birth): presence of the Y chromosome leads to production of androgens resulting in male sexual differentiation
INFANCY AND CHILDHOOD: androgen production is low
what happens to testosterone production during puberty? where is it produced? and what is the immediate effect? how is this achieved?
- increases dramatically
- produced by the testes
- sperm production begins
- this is achieved from a delicate interplay of FSH and LH stimulation on two cell types in the testes
what is the interplay of FSH and LH that leads to testosterone production and sperm maturation?
FSH stimulates Sertoli cells and triggers sperm maturation
LH causes the interstitial cells to produce testosterone
what are the 2 major roles of testosterone in male sexual development?
- develops and maintains the male reproductive system
- results in the development of secondary sexual characteristics
what are 3 secondary sexual characteristics in men?
- facial and axillary hair
- voice deepening
- increased muscle and bone mass
what is the level of testosterone production in adulthood, and then as adulthood continues?
high into adulthood
declines with age
how does testosterone participate in a negative feedback loop?
testosterone exerts negative feedback on the hypothalamus and anterior pituitary so that production is kept within an appropriate range
what is the main method of control of the ovaries, where do ovaries derive from, and what do ovaries produce?
- under control of FSH and LH secreted by the anterior pituitary
- derive from the same embryonic structures as the testes
- produce estrogens and progesterone
what are estrogens secreted in response to and what do they lead to (3)?
secreted in response to FSH
- development and maintenance of the female reproductive system and female secondary sexual characteristics
- in the embryo: stimulate reproductive tract development
- in adults: lead to thickening of the lining of the uterus (endometrium) each mont in preparation for the implantation of a zygote
what are 3 secondary sexual characteristics for women?
- breast growth
- hip widening
- changes in fat distribution
mnemonic: role of estrogen and progesterone
ESTrogen ESTablishes and PROgesterone PROtects the endometrium
what is progesterone secreted by and in response to what?
what is the main role of progesterone
secreted by the corpus luteum in response to LH
involved in the development and maintenance of the endometrium (but NOT in the initla thickening)
defn: corpus luteum
the remains of the ovarian follicle following ovulation
the corpus luteum atrophies and ceases to function at the start of the first trimester, where does progesterone come from at this point?
supplied by the placenta
what are the reproductive years in a woman in biological terms?
from menarche to menopause
what are the 4 phases of the menstrual cycle?
- follicular phase
- ovulation
- luteal phase
- menstruation
what is a quick summary of the menstrual cycle? (4)
- follicles mature during the follicular phase (FSH, LH)
- LH surge at midcycle triggers ovulation
- ruptured follicle becomes corpus luteum (which secretes estrogen and progesterone) to build up uterine lining in preparation for implantation; LH and FSH are inhibited
- If fertilization does not occur, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again
what is human chorionic gonadotropin (hCG), what does it do, and explain the levels of this and other hormones throughout pregnancy (3)?
IF FERTILIZATION HAS OCCURRED: the resulting zygote will develop into a blastocyst that will implant in the uterine lining and secrete hCG
hCG is an analog of LH (looks very similar chemically and can stimulate LH receptors)
hCG maintains the corpus luteum
- critical during first trimester development because the estrogen and progesterone secreted by the corpus luteum keep the uterine lining in place
- second trimester: hCG levels decline bc the placenta has grown to a sufficient size to secrete enough progesterone and estrogen by itself
- the high levels of estrogen and progesterone continue to serve as negative feedback on GnRH secretion
defn + process: menopause (3)
- with aging, the ovaries become less sensitive to FSH and LH resulting in ovarian atrophy
- as estrogen and progesterone levels drop, the endometrium also atrophies and menstruation stops
- the negative feedback on FSH and LH is removed, so the blood levels of these two hormones rise
