Lecture Final: Chapter 27 Flashcards
Asexual reproduction
F
B
F
P
Other variants (2)
Fission: parent separates into two approximately equally sized offspring (genetic clones)
Budding: mitotic growth of a new offspring from the parent’s body (also genetic clones)
Fragmentation and regeneration: pieces separate from adult body and regenerate into new individual
Parthenogenesis: mitotic development of an unfertilized egg; may or may not be a genetic clone; may be either female or male; maybe either haploid / diploid
– Wasps / bees / ants: females are the only diploid; males will be haploid – queen has the choice to fertilize an egg that passes through
Many tropical reef fish (ie wrasse) can alter their gender over time – sequential hermophrodites
- Protandrous: male first
- Protogynous: female first
Many segmented worms are simulateneous (both sexes at once)
Asexual vs Sexual
- Gene inheritance through generations
- benefits
ASEXUAL: offspring inherit all of parents genes
@ third generation, everyone is still inheriting the family matriarch’s genes
@ fourth, again 100%
Benefits:
- preserve genetic uniformity
- no energy expended in producing gametes or finding a mate
Sexual: offspring will inherit at most 50% of parent’s genes
@ third generation, at most 25% of family matriarch’s genes
@ fourth, at most 12.5%
Benefits:
- increased genetic variability as a buffer against environmental uncertainty
- Diploidy allows for homologous recombination in DNA repair
- Diploidy can also buffer against presence of deleterious alleles
External vs Internal Fertilization
Semelparous vs Iteroparous
EXTERNAL: usually in medium of water; common to fish / amphibians / algae
- No copulation; gametes released into water
- Excessive amounts of gametes produced to increase chances of fertilization
- Zygotes develop outside male and female parents
INTERNAL: usually terrestrial beings, ie plants / reptiles / birds / mammals
- Copulation occurs, gametes shed into a confined space, leading to increased chances of fertilization
- Fewer gametes produced in order to save body materials
- Zygote can be retained inside female’s body for protection until fully developed
** both will have male gametes swimming to female gametes
Semelparous: reproduce once and die → strenuous life, go big or go home
– Anadromous salmon: animals that are born in freshwater streams, mature in seawater, swim home to freshwaters to reproduce
Iteroparous: reproduce over and over again
– Humans and their large families
Reproductive anatomy of human male (7)
4sub3
Seminiferous tubules: location of sperm production; found within lobules
Testes: suspended outside bc sperm need slightly cooler temperature to mature as they become motile in the epididymis
Vas deferens: tube of ejaculation to urethra; usually severed in a vasectomy – still ejaculate fluid but will have no sperm in it
Seminal vesicles: secrete viscous, alkaline fluid containing various substances
- Fructose: energy source
- Prostaglandins: stimulate reverse peristalsis in uterus to move sperm up; can also be stimulated during labor to push baby out
- Coagulating glands allow for no fast / slow block to polyspermy bc they hang out and mature inside uterus
Prostate gland secretes a milky, slightly acidic fluid with citrate
Bulbourethral glands secrete a lubricating mucus into lumen; will clean the urethra before ejaculation
Urethra: sperm exits as semen at a slightly basic pH
Spermatogenesis + N/C
creation of sperms
2n, 2c (mitosis yields spermatogonia B )
> 2n, 4c (mitosis yields primary spermatocytes)
> > 1n, 2c (meiosis 1 yields secondary spermatocytes)
> > > 1n, 1c (meiosis 2 yields spermatids)
Spermatogonia stem cells divide mitotically into two daughter cells A and B
- A remains at basal lamina surface as stem cell
- B cell (spermatogonia 2n, 2c) replicates becoming primary spermatocytes (2n, 4c)
Cytoplasmic bridges between spermatocytes enables molecular exchange and synchronization
– In humans, the X chromosome is one of the most genetically rich ones. Uniquely X chromosomes (versus Y chromosomes), therefore have lots of X linked diseases expressed in males (ie color blindness, muscle dystrophy)
Sertoli cells (sustentocytes) seal around developing sperm cells (blood testis barrier; sealed with tight junctions); provide nutrients, secrete androgen / binding proteins / inhibin -- Inhibin: enzyme that travels to brain that stop testosterone production; allows for controlled production of testosterone
HYPOTHALAMIC PITUITARY GONADAL AXIS
Allow for steady testosterone and sperm production
- Hypothalamus releases GnRH into hypophyseal portal system to activate anterior pituitary.
- - GnRH: Gonadotropin-releasing hormone; aka gonadoliberin - Anterior pituitary secretes FSH and LH into blood stream
- - FSH: stimulates Sertoli cells to release androgen-binding protein to keep [testosterone] high
- - LH: binds to Leydig cells for testosterone production - Testosterone will trigger spermatogenesis – rising levels will feedback negatively to hypothalamus and anterior pituitary
- Sertoli cells produce inhibin, which will inhibit release of FSH and LH from anterior pituitary
Reproductive anatomy of the female (4)
Ovaries: paired; contain germ tissue where ova are produced via meiosis
– Also function as endocrine glands, producing estrogen and progesterone → influence secondary sexual characteristics in a women + uterine lining in preparation of a fertilized egg
Oviducts: catches released ova by FIMBRIAE (will sweep egg into oviduct; fingerlike projections); location of fertilization in the region called ampulla
Uterus: site of pregnancy; wall has three layers
- Perimetrium: outermost serous layer
- Myometrium: bulky middle layer of smooth muscle; used for contractions
- Endometrium: innermost mucosal lining that responds to hormones produced by the ovary to thicken / will be shed
Vagina: birth canal with acidic pH to minimize infections
(created from lactic acid caused by bacteria working on glycogen)
Oogenesis (6) + N/C
creation of ovum
2n, 2c (Oogonium goes through mitosis)
> 2n, 4c [DNA replication then goes through meiosis 1 (stalled at prophase 1), yields primary oocyte]
> > 1n, 2c [meiosis 1 (completion), yields secondary oocyte]
> > > 1n, 1c [ovulation and fertilization yields fertilized egg ; meiosis 2 completed]
- Each oogonium becomes surrounded by a single layer of squamous cells (now a PRIMORDIAL FOLLICLE) → oogonium replicates DNA and enters into meiosis 1, where it stalls at prophase 1 (now a PRIMARY OOCYTE) – occurs before you’re born
- About a year before its possible ovulation, surrounding squamous cells become cuboidal (now a PRIMARY FOLLICLE) and oocyte enlarges
- At beginning of ovarian cycle, 14 to 20 primary follicles begin developing due to FSH. Follicle cells become stratified (now a SECONDARY FOLLICLE); these cells convert androgens into estradiol and provide it and nutrients to growing oocyte
- By day 9, only one secondary follicle (usually) remains
- LH surge on day 14 triggers primary oocyte to complete meiosis 1 (stalls at meiosis 2) becoming a secondary oocyte, soon followed by ovulation
- - ovulation in rats yield ova; in humans, yields secondary oocyte - Meiosis 2 completed only at fertilization
Female Ovarian Cycle
Follicular phase (5)
+ ovulation
+ luteal phase
- Cohort of primary follicles (each with primary oocyte stalled at prophase 1) begin to grow stimulated by FSH.
- When >1 layer of follicle cells (granulosa cells), now called secondary follicle
- Mid-phase, one dominant secondary follicle survives dip in [FSH]
- Connective tissue layer forms around follicle (theca = source of androgens in response to LH); also, glycoprotein-rich layter, zona pellucida, forms around primary oocyte
- Graafian (mature) follicle forms, and primary oocyte completes meiosis 1 (now a secondary oocyte)
Ovulation: LH surge triggers expulsion of secondary oocyte from ovary within 24-36 hours; zona pellucida and granulosa cells removed
Luteal Phase: ruptured follicle secretes progesterone (steroid hormone that stimulates uterus in preparation for pregnancy)
Female reproductive cycle – talking about hormones
GnRH
Follicular phase (2)
+ ovulation
+ luteal phase (2)
GnRH from hypothalamus releases FSH and LH from anterior pituitary into bloodstream
- LH: stimulates thecal cells to secrete andorgens; creation of corpus luteum
- FSH: stimulates granulosa cells to convert androgens to estrogens
- Estrogen: stimulate growth of primary oocyte and proliferation of granulosa cells
FOLLUCLAR PHASE
- EARLY: estrogens in blood with negative feedback on LH and FSH secretion
- LATE: estrogens with positive feedback trigger LH surge → triggers completion of
OVULATION: release of secondary oocyte
LUTEAL PHASE: Ruptured follicle now corpus luterum, will synthesize progesterone and estrogen to maintain endometrium
- Rising [progesterone and estrogen] exerts negative feedback on release of LH and FSH → Declining levels of LH and FSH prevent maturation of new follicles and corpus luteum degenerates
- Declining [progesterone and estrogen] cause endometrium to slough off and begin mentrual flow → negative inhibition of LH and FSH removed, initiating a new cycle
** Variation in time of follicular phase – after ovulation, luteal phase will rigidly follow the 14 day time frame.
Fertilization lab with sea urchins (5)
Marine animals: traditional way to reproduce is to eject their gametes into the water and just let them have at it; usually released in a synchronized manner (in lab, will use CaCl as trigger)
- Swimming sperm comes in contact egg molecules in jelly coat, triggering acrosomal reaction
- - Jelly coat: maintain species to species recognition - Acrosome releases enzymes that digest a path through jelly coat.
- - Acrosome: sac at the top of sperm head; derived from the golgi → when it recognizes the proteins in the jelly coat of the egg, it will burst to release the enzymes - Species-species recognition btwn acrosomal process of sperm and receptor proteins on egg triggers PM (plasma membrane) fusion when the sperm-binding receptors trigger
- - Vitelline layer: surrounds the outer surface of PM of ovum
- - Polyspermy: fertilization by more than one sperm; lethal for an egg - Entry of sperm nucleus causes an influx of Na+ (more positive inside) > egg rapidly depolarizes > prevents additional sperm from binding to PM → FAST BLOCK to polyspermy via electrical barrier
- Depolarization of egg opens Ca2+ channels in the ER > creation of fertilization envelope → SLOW BLOCK to polyspermy via physical barrier (happens in humans)
- - One of the cortical enzymes is a trypsin-digesting protease that cleaves proteins attaching vitelline layer to the PM layer of the egg.
Formation of human zygote and early post fertilization events
- Fertilization occurs when cytoplasm of egg and sperm become continuous
- Two events quickly follow
- - Cortical reaction
- - Completion of meiosis 2 by secondary oocyte - Rising levels of progesterone from corpus luteum relax smooth muscles of oviduct and newly fertilized egg moves down towards uterus
- Within 24 to 36 hours post fertilization, first mitotic cell division
- - Division continues occur until blastocyst forms (hollow ball of 500 to 2000 cells)
- - S > M > S > M → blastomeres become smaller and smaller
- - Hollow to facilitate delivery of nutrients (bc if not hollow, then unable to obtain nutrients) - Three days before implantation, blastocyst “hatches” from fertilization envelope (hardened zona pellucida)
- - Trophoblasts: secrete proteases that degrade fertilization envelope; secrete hormone HCG (human chorionic gonadotropin) (peptide hormone v close in sequence to LH) – will bind to cells of corpus luteum to maintain production of progesterone so that endometrium is not sloughed off → will be maintained for a few weeks
