Lecture Final: Chapter 27

Question 1

Asexual reproduction

F
B
F
P

Other variants (2)

Answer 1

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)

Question 2

Asexual vs Sexual

• Gene inheritance through generations
• benefits

Answer 2

ASEXUAL: offspring inherit all of parents genes

@ third generation, everyone is still inheriting the family matriarch’s genes
@ fourth, again 100%

Benefits:

1. preserve genetic uniformity
2. 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:

1. increased genetic variability as a buffer against environmental uncertainty
2. Diploidy allows for homologous recombination in DNA repair
3. Diploidy can also buffer against presence of deleterious alleles

Question 3

External vs Internal Fertilization

Semelparous vs Iteroparous

Answer 3

EXTERNAL: usually in medium of water; common to fish / amphibians / algae

1. No copulation; gametes released into water
2. Excessive amounts of gametes produced to increase chances of fertilization
3. Zygotes develop outside male and female parents

INTERNAL: usually terrestrial beings, ie plants / reptiles / birds / mammals

1. Copulation occurs, gametes shed into a confined space, leading to increased chances of fertilization
2. Fewer gametes produced in order to save body materials
3. 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

Question 4

Reproductive anatomy of human male (7)

4sub3

Answer 4

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

Question 5

Spermatogenesis + N/C

Answer 5

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

Question 6

HYPOTHALAMIC PITUITARY GONADAL AXIS

Answer 6

Allow for steady testosterone and sperm production

1. Hypothalamus releases GnRH into hypophyseal portal system to activate anterior pituitary.
   - - GnRH: Gonadotropin-releasing hormone; aka gonadoliberin
2. 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
3. Testosterone will trigger spermatogenesis – rising levels will feedback negatively to hypothalamus and anterior pituitary
4. Sertoli cells produce inhibin, which will inhibit release of FSH and LH from anterior pituitary

Question 7

Reproductive anatomy of the female (4)

Answer 7

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)

Question 8

Oogenesis (6) + N/C

Answer 8

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]

1. 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
2. About a year before its possible ovulation, surrounding squamous cells become cuboidal (now a PRIMARY FOLLICLE) and oocyte enlarges
3. 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
4. By day 9, only one secondary follicle (usually) remains
5. 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
6. Meiosis 2 completed only at fertilization

Question 9

Female Ovarian Cycle

Follicular phase (5)
+ ovulation
+ luteal phase

Answer 9

1. Cohort of primary follicles (each with primary oocyte stalled at prophase 1) begin to grow stimulated by FSH.
2. When >1 layer of follicle cells (granulosa cells), now called secondary follicle
3. Mid-phase, one dominant secondary follicle survives dip in [FSH]
4. Connective tissue layer forms around follicle (theca = source of androgens in response to LH); also, glycoprotein-rich layter, zona pellucida, forms around primary oocyte
5. 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)

Question 10

Female reproductive cycle – talking about hormones

GnRH
Follicular phase (2)
+ ovulation
+ luteal phase (2)

Answer 10

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.

Question 11

Fertilization lab with sea urchins (5)

Answer 11

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)

1. Swimming sperm comes in contact egg molecules in jelly coat, triggering acrosomal reaction
   - - Jelly coat: maintain species to species recognition
2. 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
3. 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
4. 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
5. 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.

Question 12

Formation of human zygote and early post fertilization events

Answer 12

1. Fertilization occurs when cytoplasm of egg and sperm become continuous
2. Two events quickly follow
   - - Cortical reaction
   - - Completion of meiosis 2 by secondary oocyte
3. Rising levels of progesterone from corpus luteum relax smooth muscles of oviduct and newly fertilized egg moves down towards uterus
4. 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)
5. 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