Biology-Animal Reproduction and Development

Question 1

Non-animal Reproduction

Answer 1

asexual reproduction: benefits from stable environment since offspring are clones; sexual reproduction’s advantage is variation

Question 2

Fission

Answer 2

separation of organism into 2 new cells (amoeba)

Question 3

budding

Answer 3

new individual splits off from existin one (hydra)

Question 4

fragmentation + regeneration

Answer 4

single parent breaks into parts that regenerate into new individuals (sponge/planaria/starfish)

Question 5

parthenogenesis

Answer 5

development of egg w/out fertilization; resulting adult is haploid (honeybees, some lizards)

Question 6

Gonads

Answer 6

reproductive structure responsible for production of gametes. Male = testis, female= ovaries (primary sex characteristics)

(secondary sex characteristics) indiction of sexual maturity but not specifically involved in reproduction (e.g. breasts)

Question 7

Female Reproduction System

Ovary

Answer 7

ova, or eggs, are produced. Each female has two ovaries

Question 8

Female Reproductive System consists of:

Answer 8

ovary, oviduct, uterus, vagina

Question 9

Female Reproductive System

Oviduct

Answer 9

eggs move from ovary to uterus through oviduct (Fallopian/uterine tube); one for each ovary; swept by fimbrae

Question 10

Female Reproductive System

Uterus

Answer 10

fertilized ovum implants (attaches) on the inside wall, endometrium, of uterus. Development of embryo occurs here until birth

Question 11

Female Reproductive System

Vagina

Answer 11

at birth, fetus passes through cervix (opening in the uterus), through and out of body

Question 12

Male Reproductive System

Male Reproductive System

Answer 12

path of sperm is SEVEnUP

SEVEnUP: seminiferous tubules ⇒epidydmis →vas deferens→ ejaculatory duct→ urethra →penis

Question 13

Male Reproductive System

Testis

Answer 13

each consists of seminiferous tubules for production of sperm and interstitial cells (Leydig cells) produces male sex hormones (testosterone = androgen) secreted in the presence of LH;

sertoli cells stimulated by FSH surround and nurture sperm (also secrete peptide hormone inhibin, acts on PitGl to inhibit FSH release);

testis contained in scrotum-about 2C lower than body temp for sperm production.

Question 14

Male Reproductive System

Epididymis

Answer 14

coiled tube, one attached to each testis; site for final maturation and storage of sperm.

Question 15

Male Reproductive System

Vas deferens

Answer 15

transfer sperms from one epididymis to urethra.

Question 16

Male Reproductive System

Seminal vesicles

Answer 16

Two glands, during ejaculation secrete into vas deferens: provide mucus (liquid for sperm), fructose as ATP, and prostaglandins (stimulate uterine contractions that help sperm move into uterus)

Question 17

Male Reproductive System

Prostate gland

Answer 17

secretes milky alkaline fluid into urethra; neutralizes acidity of urine that may still be in urethra, also vagina acidity. Also neutralizes seminal fluid (too acidic from metabolic waste of sperm)

Question 18

Male Reproductive System

Bulbourethral glands (aka Cowper’s)

Answer 18

secrete small amount of fluid of unknown function into urethra

Question 19

Male Reproductive System

Penis

Answer 19

transport semen (fluid containing sperm and secretions) into vagina.

Question 20

Sperm

Sperm

Answer 20

compact packages of DNA specialized for effective male genome delivery.

Question 21

Sperm

Sperm head

Answer 21

haploid (23 chromosomes); at tip is acrosome (a lysosome containing enzymes [hyaluronidase] which are used to penetrate egg-originates from Golgi body vesicles that fused together). Only nuclear portion of sperm enters the egg.

Question 22

Sperm

Midpiece

Answer 22

flagellum (9 + 2 microtubule array), lots of mitochondria

Question 23

Sperm

Tail

Answer 23

remainder of flagellum; sperm is propelled by whiplike motion of tail and midpiece.

Question 24

Gametogenesis in Humans

Gametogenesis in Humans

Answer 24

It is the meiotic cell divisions that produce eggs (oogenesis) and sperm (spermatogenesis). Egg contains most of the cytoplasm, RNA, organelles, and nutrients needed by developing embryo.

• oogenesis
• ovulation
• spermatogenesis

Question 25

Gametogenesis in Humans

Oogenesis

Answer 25

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

Question 26

Gametogenesis in Humans

Ovulation

Answer 26

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)

Question 27

Gametogenesis in Humans

Spermatogenesis

Answer 27

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

Question 28

Gametogenesis in Humans

Sertoli cells

Answer 28

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.

Question 29

Gametogenesis in Humans

Capacitation

Answer 29

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

Question 30

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Female Reproductive Cycle

Answer 30

ovarian cycle (ovary) + menstrual cycle (uterus)

Question 31

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Menstrual Cycle (uterus)

Answer 31

divided into follicular, ovulation, luteal, menstruation (proliferative/secretory/menstruation)

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

Question 32

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Menstrual Cycle (No Implantation)

Answer 32

(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.

Question 33

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Menstrual Cycle (Implantation)

Answer 33

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

Question 34

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Ovarian Cycle

Answer 34

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.

Question 35

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Estrogen

Answer 35

thicken endometrium

Question 36

Hormonal Control of Human Reproduction: Female Reproductive Cycle

Progesterone

Answer 36

development and maintenance of endometrial wall

Question 37

Hormonal Control of Human Reproduction:

Male Reproductive Cycle

Answer 37

• 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.

Question 38

Embryonic Development

Four stages in growth and development of animal

Answer 38

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

Question 39

Embryonic Development

In mammals, development is two stages

Answer 39

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

Question 40

Embryonic Development

Stages of Embryonic Development

Answer 40

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

Question 41

Embryonic Development: Fertilization

Fertilization

Answer 41

sperm penetrate plasma membrane of 2nd oocyte.

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).

Question 42

Embryonic Development: Fertilization

Zona Pellucida

Answer 42

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).

Question 43

Embryonic Development

Cleavage

Answer 43

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

Question 44

Embryonic Development

Morula

Answer 44

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

Question 45

Embryonic Development

Blastula

Answer 45

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

Question 46

Embryonic Development

Gastrula(tion)

Answer 46

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).

Question 47

Embryonic Development: Extraembryonic membrane development

Extraembryonic membrane development

Answer 47

In birds, reptiles, and humans (called amniotes), this develops as follows:

1. Chorion
2. Allantois
3. Amnion
4. Yolk Sac

Question 48

Embryonic Development: Extraembryonic membrane development

Chorion

Answer 48

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)

Question 49

Embryonic Development: Extraembryonic membrane development

Allantois

Answer 49

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.

Question 50

Embryonic Development: Extraembryonic membrane development

Amnion

Answer 50

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

Question 51

Embryonic Development: Extraembryonic membrane development

Yolk Sac

Answer 51

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.

Question 52

Embryonic Development: Organogenesis

Organogenesis

Answer 52

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)

Question 53

Embryonic Development: Exceptions to the General Embryonic Development Patterns

Frog

Answer 53

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

Question 54

Embryonic Development: Exceptions to the General Embryonic Development Patterns

Bird

Answer 54

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.

Question 55

Embryonic Development: Exceptions to the General Embryonic Development Patterns

Humans and most other mammals

Answer 55

a. Blastocyst: blastula stage consisting of two parts—outer ring of cells (trophoblast) and inner mass of cells (embryonic disc).

• 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)

Question 56

Embryonic Development: Factors that Influence Development

Factors that Influence Development

Answer 56

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

Question 57

Factors that Influence Development

Influence of the egg cytoplasm

Answer 57

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.

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.

Question 58

Factors that Influence Development

Embryonic Induction

Answer 58

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

Question 59

Factors that Influence Development

Homeotic genes

Answer 59

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)

Question 60

Factors that Influence Development

Apoptosis

Answer 60

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.

Question 61

Factors that Influence Development

Determined

Answer 61

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.

Question 62

Factors that Influence Development

Labor (three stages)

Answer 62

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

Question 63

Factors that Influence Development:

Fraternal vs. Identical Twins

Answer 63

**Fraternal twins **result from more than one egg being fertilized

Identical twins result from indeterminate cleavage

Question 64

Amniotes

Answer 64

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