chapter 46 animal reproduction. overview of sexual reproduction

Chapter 46 Animal Reproduction

Overview of sexual reproduction

Both asexual and sexual reproduction occur in the

animal kingdom

sexual reproduction : fusion of haploid gametes to

form a zygote, fertilized eggs

Female gamete: ovum

Male : spermatozoon

Diverse mechanisms of asexual reproduction

enable animals to produce identical offspring

invertebrate: fission

budding

fragmentation and regeneration

Figure 46.0x1 Utethesia ornatrix mating

Figure 46.0x2 Red beetles mating

Figure 46.1 Two from one: asexual reproduction of a sea anemone (Anthopleura elegantissima)

Figure 46.x1 Aphid giving live birth

reproductive cycle and pattern vary extensively

among animals

1. Most animals shows definite cycles in reproductive

activity

2. Controlled by hormonal and environmental cues (temperature, rainfall, day length and lunar cycle)

parthenogenesis: eggs develop without fertilization

fig 46.2

Figure 46.2 Sexual behavior in parthenogenetic lizards

(a)

3. Reproduction may alternate between sexual and

asexual

hermaphrodite: individuals has both male and female

reproductive system( for sessile and

burrowing animals)

sequential hermaphrodite

protogenous : female first

protandrous: male first

figure 46.3

Figure 46.3 Sex reversal in a sequential hermaphrodite

Mechanisms of sexual reproduction

fertilization: Internal fertilization

External fertilization

Internal and External fertilization both depend on Internal and External fertilization both depend on

mechanisms ensuring that mature sperm encounter mechanisms ensuring that mature sperm encounter

fertile eggs of the same speciesfertile eggs of the same species

1. Internal fertilization

a. require cooperative behavior,lading to copulation

b. require sophisticated reproductive system

2. External fertilization

a. an environment where eggs can develop without

desiccation or heat stress

Figure 46.0 Frogs mating

Figure 46.4 The release of eggs and external fertilization

Species with internal fertilization usually produce

fewer zygotes but provide more parental protection

than species with external fertilization

a. External fertilization

less protection for eggs and fertilized zygotes

b. Internal fertilization

protection by: egg shells

develop within reproductive tract

pouches for marsupials

Figure 46.x2 Sea urchin sperm fertilizing an egg

Figure 46.5 Parental care in an invertebrate

Complex reproductive systems have evolved in

animal phyla( phylum Annelida)

1. Polychaete( 多毛綱 )

separate sex, but no distinct gonads

eggs and sperms develop from undifferentiated

linings of the coelom

gametes release from body wall and fill the

coelom as they mature

2. Flat worm ( Phylum Platyhelminthes)

hermaphroditic

sperms may ejected to female reproductive

system of another individual

Figure 46.6 Reproductive anatomy of a parasitic flatworm

2. Insects

separate sex with complex reproductive system

sperm develop in a pair of testes and stored in the

seminal vesicles

eggs develop in a pair of ovaries

female may store sperms in spermatheca

Figure 46.7 Insect reproductive anatomy

Mammalian reproductive system

Figure 46.8 Reproductive anatomy of the human male

尿囊貯精囊

輸精管

尿道球腺睪丸副睪

陰囊 包皮

龜頭

尿道前列腺

Figure 46.8 Reproductive anatomy of the human male

尿道

陰囊

尿囊

睪丸副睪

輸精管

龜頭

前列腺尿道球腺

貯精囊

Spermatogenesis

The production of mature sperm cells

a ejaculation of human male contain 100-650

million sperms

Figure 46.11 Spermatogenesis

Figure 46.11x Spermatogenesis: Seminiferous tubules (left), sperm in semen (right)

Figure 46.12 Structure of a human sperm cell

Figure 46.9 Reproductive anatomy of the human female

輸卵管

卵巢子宮

尿囊

尿道

陰蒂

大 ( 小 ) 陰唇

陰道

尿道球腺

子宮頸

Figure 46.9 Reproductive anatomy of the human female

Oogenesis

The development of ova( mature, unfertilized

egg cells)

Egg cells stays at prophase of meiosis I until

puberty

Figure 46.13a Oogenesis

Birth to puberty

Stimulation of FSH

Figure 46.9x Ovary (left) and follicle (right)

Figure 46.10 Ovulation

Figure 46.13b Oogenesis

Figure 46.15 The reproductive cycle of the human female

shedding of

endothelium lining

雌激素黃體激素

Differences of Oogenesis and spermatogenesis

1. Cytokinessis of meiotic division in oogenesis is

unequal ( polar body degenerate)

2. Mitosis continues thought the male’s life

3. Oogenesis has long ‘resting period’

A complex interplay of hormone regulates reproduction

The male pattern

Androgen ( 雄激素 )---- testosterone

Produced by ledig cells of testes

Responsible for 1st and 2nd sex characteristics

development of vas deferentia, development of

external reproductive structure, sperm

production

The aggressiveness of male behavior is enhanced

by androgen

Figure 46.14 Hormonal control of the testes

下視丘

腦下垂體

濾泡刺激激素

The female pattern

Ovulation occurs during menstrual cycle( shedding of

endothelium lining of uterus) or estrous(endothelium

lining cycle

More pronounced behavior change for estrous cycle

than menstrual cycle

Average of 28 days for menstrual cycle

Ovaries lose their response to FSH and LH during

menopause (age 46-54)

Embryonic and fetal development occur during pregnancy in human and other placental animals

Figure 46.16 Formation of the zygote and early postfertilization events

Reproductive Immunology

Interference of immune response by trophoblast:

1. Produce chemical signal induce suppressor T cell

which prevent other T cell from foreign tissue

2. Secret enzyme that break down tryptophan that is

necessary for T cell survival

3. A mouse protein produced by trophoblast protect

embryo from been attacked by complement

Figure 46.17 Placental circulation

Figure 46.18 Human fetal development

5 weeks 14 weeks 20 weeks

Figure 46.19 Hormonal induction of labor

Figure 46.20 The three stages of labor

Contraception: prevention of pregnancy

1. Prevent release of mature eggs and sperm from gonads

2. Prevent fertilization by keeping eggs and sperms apart

3. Prevent implantation

4. Abortion

Birth control pill

1. Combination of synthetic estrogen and progestin

negative feedback to inhibit release of GnRH

prevent ovulation

2. Minipill ( progestin)

alter cervical mucus to block sperm from

entering

Figure 46.21 Mechanisms of some contraceptive methods

Figure 46.22 Ultrasound imaging

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