Download begins during female`s embryonic development Ovaries

I. Types of reproduction
A. Asexual Reproduction
1. Only 1 parent
2. Example: Animalia (Porifera, Cnidaria,
Platyhelminthes, Annelida), Plantae,
Fungi, Monera, Protista
•
Hydrozoa and scyphozoa
typically reproduce by
budding asexually.
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.
1) Identical organisms
are susceptible to the
same environmental
challenges.
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
Sexual Reproduction +/• Advantages
– VARIETY
• Disadvantages
– Timing
– Mate
appeasement
– slower
C. Parthenogenesis-an unusual case
1. Reproduction w/ one type of sex cell.
2. Haploid Eggs develop w/out fertilization
3. Ex. Brahminy Blind Snake is parthenogenic
and has only sterile females.
4. Turkey, Daphnia, Whiptail lizards
Whiptail lizard
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
External
fertilizers
must
produce
large
numbers of
eggs.
Many young are
produced to ensure the
survival of a few
Mating ball formed as multiple males
amplex on one female.
Who’s yo’ Daddy?
Water borne eggs are exposed
to chemicals in the water
(these mutants are from
Minnesota)
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)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
occurs from Puberty until death!
Seminiferous tubules~ location
Primordial germ cells (2N)~ differentiate into….
Spermatogonia (2N)~ sperm precursor
divide Repeated through mitosis into….
Primary spermatocytes (2N)
start meiosis (1st meiotic division)
produces 2 Secondary spermatocytes (2N)
2nd meiotic division
produces 4 Spermatids (1N)~
Sertoli cells provide nourishment as they mature into…
Sperm cells (1N)
m. spermatogenesis is controlled by hormones
1) LH stimulates testes to produces testosterone…
2) FSH stimulates Sertolli cells to promote the dev of
sperm
3) hormone & gamete production are constant
3. Oogenesis
begins during female’s embryonic development
Ovaries - location
fetal Primordial germ cells (2N) called oogonia
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
a)
b)
c)
d)
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
1) deuterostomes – radial cleavage where cells are
aligned with each other (chordates)
2) protostomes – spiral cleavage where cells are
slightly offset from each other
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
recap
1. fertilization
2. cleavage
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 2layered 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