Download AP Biology: Reproduction I. Types of reproduction A. Asexual

AP Biology: Reproduction
I. Types of reproduction
A. Asexual Reproduction1. Only 1 parent
2. Example: Animalia (Porifera, Cnidaria, Platyhelminthes, Annelida), Plantae, Fungi,
Monera, Protista
3. Advantages of Asexual Reproduction
a. Rapid production of offspring
b. No mate appeasement
c. Timing not significant
4. Disadvantages to Asexual
a. Produces identical offspring
b. Eliminates variation
c. Makes species susceptible to extinction.
B. Sexual Reproduction
1. 2 parents produce offspring that have unique combos of genes inherited from the
gametes of the parents
2. disadvantages of sexual repro
a. Mate appeasement required.
b. Timing of sperm placement is important.
c. Slower than asexual (normally)
3. Advantages to Sexual Reproduction -- variety
C. Parthenogenesis-an unusual case
1. Reproduction w/ one type of sex cell.
2. Eggs develop w/out fertilization
3. Ex. Brahminy Blind Snake is parthenogenic and has only females.
4. other; Turkey, Daphnia, Whiptail lizards
II. Fertilization– union of sperm & egg
A. External Fert – fertilization of egg outside of the female’s body
1. External fertilization advantages & disadvantages
a. + less mate appeasement
b. requires large volumes of gametes
c. require large numbers of offspring
B. Internal Fertilization – sperm fertilizes egg inside female
1. advantages & disadvantages
a. (-) Mate appeasement and attraction is required
b. (+) produces smaller number of offspring
c. (-) must raise offspring
C. Capacitation of Sperm
1. Sperm are incapable of penetrating an oocyte unless they are capacitated
2. Capacitation: the process by which the acrosomal region of a sperm becomes
weakened
3. This allows hydrolytic enzymes to be released from the sperm near the oocyte
4. Why is polyspermy bad?
a. Polyspermy is prevented in humans by:
1). Fast block to polyspermy
a) Depolarization of the membrane
b) Prevents other sperm from fusing with oocyte membrane
2). Slow block to polyspermy
a) Releases cortical granules and forms fertilization membrane
b) Detaches all sperm in contact with the oocyte membrane
5. What about sperm from other species?
a. special receptor proteins on egg that recognize proteins on the sperm --1) that means it’s species specific!
D. Gametogenesis
1. production of gametes
2. Spermatogenesis
a) occurs from Puberty until death!
b) Seminiferous tubules~ location
c) Primordial germ cells (2N)~ differentiate into….
d) Spermatogonia (2N)~ sperm precursor
e) divide Repeated through mitosis into….
f) Primary spermatocyte s(2N)
g) start meiosis (1st meiotic division)
h) produces 2 Secondary spermatocyte s(1N)
i) 2nd meiotic division
j) produces 4 Spermatids (1N)~
k) Sertoli cells provide nourishment as they mature into…
l) Sperm cells (1N)
3. Oogenesis
a) begins during female’s embryonic development
b) Ovaries - location
c) fetal Primordial germ cells (2N) called oogonia
d) form Primary oocytes (2N) – each oocyte has an envelop of “caretaking” cells
called a follicle
e) Between birth & puberty oocytes suspended in prophase I of meiosis
f) at Puberty FSH triggers completion of meiosis I with unequal cytokinesis – this
makes sure that the developing embryo (later) has enough organelles …. for survival
g) Secondary oocyte (1N) -with most of the cytoplasm -is formed & the other is a
polar body (ultimately disintegrates)
h) ovulation allows oocyte to be released from ovary
i) Meiosis II begins when stimulated by fertilization
j) an Ovum (1N) & 2nd polar body are formed (polar body disintegrates)
E. Female Reproductive Cycle
Follicular Phase
1. Pituitary releases FSH & LH (neg. feedback – low levels of estrogen &
progesterone cause pit to secrete FSH –controlled by hypothalamus)
2. FSH stimulates development of follicle in ovary
3. follicle secretes estrogen
Ovulation Phase
4. ↑ levels of estrogen (pos feedback) cause pit to release LH which triggers ovulation
Luteal Phase
5. what’s left over of the follicle is called the corpus luteum – it secretes Estrogen &
Progesterone
6. E & P cause endometrium (lining of uterus) to thicken
7. high levels of E & P cause pituitary to stop producing FSH & LH (neg feedback) –
termination of cycle
8. no FSH & LH causes corpus luteum to deteriorate– so no E & P
9. No E & P means endometrium disintegrates & is sloughed off during menstruation
If egg is fertilized & implanted
10. if embryo implants it secretes HCG (human chorionic gonadotropin) that keeps the
corpus luteum alive functional (making E & P)
a. if no HCG – no E & P & menstruation would begin resulting in spontaneous
abortion
** pregnancy tests check for HCG in urine!
11. later HCG is replaced by P produced by placenta so, technically the embryo
maintains the pregnancy
III. Embryonic development
A. similar processes occur in most animals
1. fertilization – combo of sperm & egg
a. developing organism now called a zygote
2. cleavage – zygote undergoes rapid cell division w/out cell growth (so each cell has
very little cytoplasm) each of these cells is called a blastomere
a. embrionic polarity –
1) upper is animal
2) lower is vegetal – contains yolk (food) which is more dense so it sinks to the
bottom
b. polar & equatorial cleavages occur
1) polar = N to S
2) equatorial = E to W
c. radial & spiral cleavages
(chordates)
other
1) deuterostomes – radial cleavage where cells are aligned with each other
2) protostomes – spiral cleavage where cells are slightly offset from each
d. indeterminate/determinate cleavage
1) when blastomeres are separated & each one can complete normal
development it’s called indeterminate cleavage
2) when blastomeres are separated the individuals CAN’T complete
development it’s called determinate cleavage (each cell has already determined how it
will develop & has already grown past the point of no return)
a) radial deuterostomes = indeterminate (embryonic stem cells)
b) spiral protostomes = determinate
3. Morula – continued cleavage makes a solid ball of cells called a morula
4. Blastula – cleavage continues- ball of cells fills with fluid & forms a hollow ball with
a single layer of cells
a. hollow area is called blastocoel
5. Gastrula – group of cells invaginates forming a 2-layered embryo w/ an opening to
the outside
a. a 3rd layer then forms between inner & outer layers – now you have the 3 germ
layers (endoderm, mesoderm, ectoderm)
b. center cavity formed = archenteron
c. opening to archenteron (blastopore) becomes anus in deuterstomes (you)
6. Extraembryonic membrane development (birds, reptiles, humans)
a. chorion – outer membrane that implants in to uterus wall (endometrium)
1) chorion + maternal tissue = placenta
2) this allows exchange of gases, nutrients, & wastes between embryo &
mother
b. allantois – encircles embryo – transports wastes & develops into umbilical cord
c. amnion – sac enclosing amniotic cavity which contains amniotic fluid that acts as a
shock absorber
d. yolk sac – empty in mammals – in birds & reptiles contains nutrients & blood
vessels to transfer nutrients to embryo
7. Organogenesis – cell differentiation – creation of tissues & organs
a. notochord- form from cells on dorsal surface of mesoderm – creates vertebra
b. neural tube – from ectoderm above notochord – a groove forms which ultimately
develops into CNS