Lecture #18: Asexual and Sexual Reproduction
"A population transcends finite life spans only by
reproduction." (p. 975)
I. MODES OF
REPRODUCTION
A. ASEXUAL
REPRODUCTION = when a single
individual produces clones that are genetically identical to itself. (It
perpetuates successful genotypes in constant environments.)
1. Fission
is the separation of a parent organism into two or more individuals (sea
anemone).
2. Budding
is when a new individual grows out from the body of the original (hydra)
(coral).
3. Fragmentation
is the natural breaking of the body into pieces that develop into complete
adults (segmented worms, e.g. annelidia, and sponges).
4. Parthenogenesis
is more like asexual reproduction, because the egg develops without being
fertilized.
B. SEXUAL
REPRODUCTION = when gametes (ova and
spermatozoa) form zygotes.
1. Recombinations
of genetic pools allow more diversity of offspring.
a. it is like
buying new clothes or shoes--if the store has only one style, the chance of
being selected is less (and the store goes out of business).
b. variety
(diversity) increases the chance of selection (and future use).
C. EXTERNAL
FERTILIZATION vs INTERNAL FERTILIZATION
1. External
requires environment that is constantly moist and has limited temp changes.
2. Internal
requires special organs, along with cooperative behavior for copulation.
II. THE THIN LINE
BETWEEN MALENESS AND FEMALENESS
1. Parthenogenic
lizards that genetically are all females: (Fig. 46.2)
a. during
breeding season, some females impersonate a male. (doubling of chromosomes
after meiosis)
b. yet, later,
when estrogen levels are higher, the impersonator may lay eggs, normally.
c. still,
initiation of courtship allows hormones to flow to maximize ovulation.
(d. compare this
to induced-ovulators, like the rabbit.)
2. Hermaphroditic
animals have both functional male and female reproductive systems.
a. some
hermaphrodites can fertilize themselves.
b. most will mate
(cross-fertilize) with another member of the same species. (Fig. 46.6)
c. twice as many
offspring can be produced from a single encounter.
III. HORMONAL
CONTROL OF MAMMALIAN REPRODUCTION
"The
omnipresent process of sex, as it is woven into the whole texture of our man's
and woman's body, is the pattern of all the process of our life." Havelock
Ellis
A. THE DIFFERENCE
BETWEEN LITTLE BOYS AND LITTLE GIRLS
1. undifferentiated at 7 weeks. (Fig. Z)
2. genital
tubercle becomes penis or clitoris.
3. urethral
folds give rise to shaft and labia minora and outer 1/3 of vagina.
4. labioscrotal
swelling gives rise to scrotum and labia majora.
B. REPRODUCTIVE
ANATOMY OF ADULT HUMANS
1. The human male
(Fig. 46.8)
2. The human
female (Fig. 46.9)
C. SEX
CHARACTERISTICS IN MALES AND FEMALES
1. The male
pattern and androgens (testosterone):
a. primary sex
characteristics are vas deferens, external genitalia, and sperm.
b. spermatogenesis
(200 million sperm/day) (Figs. 46.11 & 46.12)
c. secondary
sex characteristics:
(1) deepening of
the voice.
(2) axillary,
facial, and pubic hair.
(3) muscle growth
(androgens promote protein synthesis).
(4) sexual
behavior and aggressiveness (bird singing and frog calling).
2. The female
pattern and estrogens (and progesterone):
a. primary sex
characteristics are oviduct/uterus, external genitalia, and eggs.
b. oogenesis
(400 eggs/lifetime) (Fig 46.13)
c. secondary
sex characteristics:
(1) deposition of
fat in the breasts and hips.
(2) stimulates
breast development.
(3) effects
calcium metabolism and water retention.
(4) mediates
female sexual behavior.
D. HORMONAL
CONTROL OF THE TESTES (Fig. 46.14)
E. HORMONAL
CONTROL OF THE OVARIES (the menstrual
cycle) (Fig. 46.15)
1. ovarian follicular
& luteal phases.
2. uterine proliferative
& secretory phases.
F. MISCELLANY ON
CONCEPTION, PREGNANCY, AND BIRTH
1. Fertilization
and post-fertilization (Fig. 46.16)
a. trophoblastic
cells of blastocyst produce hCG to retain corpus luteum.
b. Pregnancy
lasts 266 days (281 days from start of last period).
2. Placental
circulation (Fig. 46.17)
3. Labor and
parturition (progesterone down and prostaglandins up) (oxytocin).
(Fig. 46.19, 46.20)