Biology-Animal Reproduction and Development Flashcards

Question

Gametogenesis in Humans Oogenesis

Answer 1

being during embryonic development; **oogonia** (fetal cells) →(mitosis) **primary oocytes** →(meiosis) and remain at Prophase I until puberty (one primary oocyte during each menstrual cycle-28days, stim’d by FSH) continue its development through remainder of meiosis I within **follicle** (protects and nourishes oocyte)→ (completion of Meiosis I) **secondary oocyte** (most of cytoplasm) + **polar body** (small cytoplasm; may or may not divide but products disintegrate) formed; now arrested at metaphase of meiosis II until → ovulation

Answer 2

releases **secondary oocyte** from **vesicular follicle** (caused by LH surge). If fertilized by sperm → (finishes meiosis II) **ovum/egg** (diploid once completely fertilized) + **polar body** (degenerate)

Answer 3

begins at *puberty* within seminiferous tubules of testes. **Spermatogonia** cells →(mitosis) **primary spermatocytes** → (meiosis) **2 secondary spermatocytes** → (meiosis II) **4 spermatids**.

Answer 4

in seminiferous tubules provide nourishment to spermatids as they differentiate into mature **spermatozoa** (sperm). They complete maturation (gain motility and are stored) in the epididymis.

Answer 5

penultimate step in maturation of the spermatozoa while in the vagina, allows for egg penetration

Answer 6

**ovarian cycle** (ovary) + **menstrual cycle** (uterus)

Answer 7

divided into follicular, ovulation, luteal, menstruation (proliferative/secretory/menstruation) ## Footnote **Hypothalamus and anterior pituitary initiate**: monitor estrogen and progesterone in blood; Low level→hypothalamus→GnRH→FSH and LH (via anterior pituitary-negative feedback)→ **Follicle develops** →FSH stimulate follicle to secrete estrogen→ lots of estrogen (positive feedback on AP) → **LH Surge** → **Ovulation** (follicle is now **corpus luteum**-maintained by LH [which along w/ estrogen begins to decrease after ovulation], secretes → estrogen + progesterone)→ **Development of endometrium** (thickens in prepn for implantation of fertilized egg)→ No implantation or Implantation

Answer 8

(*negative-feedback* on AP from ↑e+p) **terminates production of FSH + LH** (due to ↓GnRH from hypothalamus)→**Corpus luteum** (no longer maintained by LH) **disintegrates** →corpus albicans, no estrogen + progesterone → endometrium shed during menstruation’s flow phase.

Answer 9

**If implantation occurs**→embryo (placenta) secretes chorionic gonadotropin (**HCG**)→maintain **corpus luteum**→ **Production of e + p** remain high → endometrium stays → HCG is later replaced by progesterone from placenta

Answer 10

1. **Follicular phase**: development of egg and secretion of estrogen from follicle. 2. **Ovulation**: midcycle release of egg. 3. **Luteal phase**: secretion of estrogen and progesterone from corpus luteum after ovulation.

Answer 11

thicken endometrium

Answer 12

development and maintenance of endometrial wall

Answer 13

* GnRH →FSH + LH (also called **ICSH**, interstitial cell stimulating hormone à testosterone and androgens from testis). * FSH and testosterone→influence **Sertoli** cells to promote development of sperms (nourish sperm during development-spermatogenesis). Hormone and gamete production are constant unlike female.

Answer 14

* gametogenesis (sperm/egg formation) * embryonic development (fertilization of egg until birth) * reproductive maturity (puberty) * aging process to death.

Answer 15

embryonic followed by fetal development. Fetus is an embryo that resembles the infant form.

Answer 16

1. Fertilization 2. Cleavage 3. Morula 4. Blastula 5. Gastrula 6. Extraembryonic membrane development 7. Organogenesis

Answer 17

sperm penetrate plasma membrane of 2nd oocyte. ## Footnote 1. **Recognition**: before penetration, sperm secretes proteins that bind with receptor that reside on glycoprotein layer (**vitelline layer-zone pellucida** in human) surrounding plasma membrane of oocyte ensures same species fertilization Note: Fertilization can be external in water (lots of eggs laid since change of fertilization is lower; e.g. frogs, amphibians) or internal (terrestrial vertebrates; # of eggs affected by internal vs. external (more eggs) early development, amount of parental care (less care = more eggs) 2. **Penetration**: plasma membranes of sperm and oocyte fuse, sperm nucleus enter oocyte. 3. **Formation of fertilization membrane**: vitelline layer forms fertilization membrane blocks additional sperm (due to **cortical reaction**: exocytosis of enzymes produced by cortical granules in egg cytoplasm during fertilization – slow block when seen in mammals) 4. **Completion of meiosis II in 2nd oocyte:** sperm penetration triggers meiosis 2; ovum + polar body (discharged through plasma membrane) produced. 5. **Fusion of nuclei and replication of DNA**: sperm and ovum nuclei fuse→zygote (diploid-23 pairs in human).

Answer 18

Glycoprotein membrane surrounding plasma membrane of an oocyte. External but essential to the oocyte. First appears in unilaminar oocytes; secreted by both the oocyte and follicular cells (at puberty FSH stimulates growth of granulosa cells around primary oocyte that secrete the viscous zona pellucoda). It binds sperm, and is required to initiate the **acrosome** **reaction** (sperm releases contents of acrosome as it approaches egg; contributes to charge based fast block of polyspermy). 5 days after fertilization, blastocyst performs **zone hatching** (zona pellucida degenerates + replaced by underlying layer of trophoblastic cells so it can implant in the uterus).

Answer 19

rapid cell divisions without cell growth; each cell = **blastomere** (less cytoplasm than original zygote) 1. **Embryo polarity**: egg has upper, **animal pole** and lower, **vegetal pole** (contain more yolk material which is denser than cytoplasm, settles at bottom; differentiates into extraembryonic membranes that protect+nourish embryo). 2. **Polar and equatorial cleavages**: early cleavages are polar, dividing egg into segments that stretch from pole to pole (segments of orange); others are parallel with equator. 3. **Radial and spiral cleavages**: radial in deuterostomes forming (indeterminate) cells at animal and vegetal poles that are aligned together, top cells directly above bottom cells. In protostomes (spiral-determinate), cells formed on top are shifted relative to those below. 4. **Indeterminate and determinate cleavages**: indeterminate (blastomeres can individually complete normal development if separated). Determinate cannot develop into complete embryo if separated; each is differentiated into part of the embryo. Note: fertilization takes place in the oviduct; cleavage while swept; embryo at blastula stage by the time it reaches the uterus for implantation

Answer 20

successive cleavage results in solid ball of cells (~8+ cells stage) (first 8 cells are totipotent)

Answer 21

cell division continues; liquid fills morula and pushes cells out to form circular cavity surrounded by single layer of cells. Blastocoel is the cavity. (~128 cells stage) * In humans the blastula is called the blastocyst and implants into the endometrium

Answer 22

invagination into blastula, forming two-layered embryo with an opening from outside into center cavity. 1. _Three germ layers_: ectoderm, mesoderm, and endoderm (3rd layer is formed between outer and inner layer of invaginated embryo). Give rise to all subsequent tissues. **Endoderm** – epithelial lining of digestive & respiratory, parts of liver, pancreas, thyroid, and urinary bladder lining **Mesoderm** – musculoskeletal, circulatory system, excretory system, gonads, connective tissue, portions of digestive & respiratory, notochord **Ectoderm** – Nervous system (brain and spinal cord), integument (epidermis & hair / epithelium of nose, mouth, anal canal), sense structures (lens of eye, retina), teeth, neural tube Note: some primitive animals (e.g. sponges, cnidarian) will develop **mesoglea**, a noncellular layer, instead of mesoderm 2. _Archenteron_: center cavity formed by gastrulation. 3. _Blastopore_: opening into archenteron, becomes mouth (protostomes) or the anus (deuterostomes).

Answer 23

In birds, reptiles, and humans (called amniotes), this develops as follows: 1. Chorion 2. Allantois 3. Amnion 4. Yolk Sac

Answer 24

outer membrane. Birds and reptiles: membrane for gas exchange. Mammals: chorion implants into endometrium, and later, the chorion and maternal tissue form the **placenta** (a blend of maternal and embryonic tissues across which gases, nutrients, and wastes are exchanged)

Answer 25

Sac that buds off from archenteron (cavity of gastrula forming primitive gut) that eventually encircles the embryo, forming layer below chorion. * Birds + reptiles: initially stores waste products as uric acid. Later fuses w/ chorion→membrane for gas exchange w/ blood vessels below. * Mammals: allantois transports waste products to placenta; eventually forms umbilical cord between embryo and placenta: transporting gases, nutrients, and wastes. Becomes urinary bladder in adults.

Answer 26

encloses **amniotic cavity**, a fluid-filled cavity that cushions the developing embryo, much like the coelom cushions internal organs in coelomates

Answer 27

In birds and reptiles, yolk sac membrane digests enclosed yolk. Blood vessels transfer nutrients to embryo. In placental mammals, yolk sac is empty, as umbilical cord/placenta delivers nutrients. **_Differences in development_** - **External development**: fish & amphibians have external fertilization in water; reptiles, birds, and some mammals (e.g. monotremes) have internal fertilization then lay eggs. No placenta. - **Non-placental internal development**: certain animals (e.g. marsupials, tropical fish) w/ no placenta either, limited exchange of food+O2 between mother/young. - **Placental internal development**: (e.g. humans). Major components are umbilical cord & placenta system: O2 received direct from mother (fetal lungs not fxnal until birth) + nutrients; CO2 and metabolic wastes removed. P & UC form from outgrowths of amnion, chorion, allantois, and yolk sac. Amnion contains amniotic fluid as shock absorber; placenta formation begins with chorion; blood vessels of allantois wall enlarge and become umbilical vessels (connect fetus → developing placenta); yolk sac (site of early development of blood vessels) becomes associated w/ umbilical vessels. Aka **viviparous** in mammals, results in live birth.

Answer 28

cells continue to divide after gastrulation→ differentiate→develop into specific tissues and organs. In chordates: 1. **Notochord**: cells along dorsal surface of mesoderm layer form notochord, a stiff rod that provides support in lower chordates. Vertebrae of higher chordates are formed from nearby cells in mesoderm. 2. **Neural tube**: In ectoderm layer directly above notochord, layer of cells forms neural plate. Plate indents, forming **neural groove**, then rolls up into a cylinder, the **neural tube**. This develops into the CNS. Additional cells roll off top of neural tube and form **neural crest** (which form teeth, bones, muscles of skull, pigment cells in skin, and nerve tissue)

Answer 29

amphibian a. **Gray crescent**: sperm penetrates frog egg → reorganization of cytoplasm → pigmented cap of animal pole rotates towards point of penetration while gray, crescent-shaped region forms opposite the point of penetration. Spemann found in early cleavage, each individual cell could develop into a frog only if it had a small portion of gray crescent. b. **Gastrulation**: blastopore forms at border between gray crescent and vegetal pole. During gastrulation, cells migrate over top edge (**dorsal lip**-formed from same region previously occupied by gray crescent) of and into blastopore in process called involution; blastocoel disappears and replaced by a different cavity (the archenteron). (this is confusing, see here for in depth explanation). Bottom edge of blastopore → **ventral lip**, side → **lateral lip**. c. **Yolk**: more extensive than sea urchin; cells from vegetal pole rich in yolk material form **yolk plug** near dorsal lip

Answer 30

a. **Blastodisc**: yolk of bird egg is very large, not involved in cleavages; cleavages only occur in blastula that consists of flattened, disk-shaped region that sits on top of yolk (**blastodisc**). b. **Primitive streak**: when gastrulation begins, invagination occurs along line called primitive streak (rather than a circle). As cells migrate into here, results in an elongated blastopore rather than circular as in sea urchins and frogs.

Answer 31

a. **_Blastocyst_**: blastula stage consisting of two parts—outer ring of cells (**trophoblast**) and inner mass of cells (**embryonic disc**). ## Footnote - Inner cell mass goes on to form the epiblast and hypoblast; epiblast is what gives rise to the endo/epi/mesoderm. b. **_Trophoblast_**: accomplishes implantation by embedding into endometrium; produces **human chorionic gonadotropin (HCG)** to maintain e+p production from **corpus luteum** (which in turn maintains endometrium); it later forms the **chorion** (later forms **placenta**). c. **_Embryonic disc_**: within cavity created by trophoblast, **inner cell mass** clusters at one pole and flatten into embryonic disc (analogous to blastodisc of birds and reptiles). Primitive streak develops→ gastrulation→development of embryo + extraembryonic membranes (except chorion)

Answer 32

1. Influence of the egg cytoplasm 2. Embryonic Induction 3. Homeotic Genes 4. Apoptosis

Answer 33

cytoplasmic material distributed unequally in egg, non-uniform distribution of cytoplasm (think gray crescent in frogs and yolk in bird eggs) results in embryonic axes, such as animal and vegetal poles. When cleavages divide egg→ daughter cells have different quality of cytoplasmic substances (**cytoplasmic determinants**). →Unique substances influence subsequent development of each daughter cell. ## Footnote **Sea urchin:** slice 8-ball embryo into two halves. Longitudinal à embryo has cells from animal & vegetal pole → normal development results. Horizontal→ embryo only has cells from animal OR vegetal→abnormal development results. Confirms the cytoplasmic determinants affecting development. Spemann confirmed with gray crescent vs none cuts.

Answer 34

influence of one cell/group of cells over neighboring cells; **organizers** (controller cells) secrete chemicals that diffuse among neighboring cells, influence their development (Dorsal lip [fxning as a primary organizer] of blastopore induces notochord development in nearby cells); 2nd dorsal lip grafted to embryo→two notochords developed

Answer 35

control of development by turning on and off other genes that code for substances that directly affect development. *Mutant* homeotic genes in fruit flies → wrong body parts in wrong places. **Homeobox** (unique DNA segment-180 nts) identifies a particular class of genes that control development (encodes homeodomain of protein that can bind DNA)

Answer 36

Programmed cell death that is a part of normal cell development. Essential for development of nervous system, operation of immune system, and destroy tissue (webbing) between fingers/toes. * Damaged cells also undergo apoptosis; if not cancer may develop. Regulated by protein activity (rather than at transcriptional/translational level); apoptosis proteins are present but inactive in normal cell. * **Mammals**: mitochondria play important role in apoptosis. * **Characteristics of apoptosis**: changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation. There is no cellular rupturing, no inflammatory response. The dead cells are engulfed. Typically affects single cells.

Answer 37

Cell is said to be **determined** if its final form cannot be changed; cytoplasmic influences narrowed by successive cell division; determination likely later than earlier. Trace cells during development to build **lineage map**.

Answer 38

a series of strong uterine contractions 1. Cervix thins out and dilates, amniotic sac ruptures and releases fluids 2. Rapid contractions followed by birth 3. Uterus contracts and expels umbilical cord and placenta

Answer 39

**Fraternal twins **result from more than one egg being fertilized **Identical twins** result from indeterminate cleavage

Answer 40

group of tetrapods (four-limbed animals with backbones or spinal columns) that have a terrestrially adapted egg; supported by several extraembryonic membranes.

Biology-Animal Reproduction and Development Flashcards

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