Reproduction

Chapter 27

Reproduction

Asexual• Genetically identical

offspring (clones)• 1 parent• No gamete fusion• Mitosis only• Pro

– Ease for nonmotile and isolated individuals, and quick

• Con– Changing environments

Sexual• Genetically unique individuals• 2 parents• Haploid gametes (n) fuse (2n)

– Egg: large, nonmotile, female– Sperm: small, motile, male

• Mitosis and meiosis• Pro

– Variability = better survival chance

• Con– Finding mates

Asexual Reproduction

• Fission– Prokaryotes– Invertebrates

• Budding– Hydras

• Fragmentation– Some sea stars & sponges

• Parthenogenesis– Bees, ants, & Komodo

dragons

Sexual Reproduction

• Simultaneous hermaphroditism– Cross-fertilization

• Sequential hermaphroditism– Many fish– Blue-banded gobies

• Separate sexes– External– Internal

FertilizationExternal Internal

HUMAN REPRODUCTIVE SYSTEMS

Female Reproductive System• Ovaries and follicles

produce estrogen• Follicles release eggs

about every 28 days• Without fertilization,

corpus luteum and endometrium degenerate– Occurs in oviduct– Zygote, embryo, fetus (9th

week)

Male Reproductive System• Sperm

– Develop in seminiferous tubules– Epididymis store while developing

• Semen– Seminal vesicles: nutrients for

energy and uterine entry– Prostate gland: nourishes and

activates – Bulbourethral glands: neutralize

urethra• Ejaculation

• Bladder sphincter contracts• Ducts and glands contract to propel

semen• Urethra sphincter relaxes• Contractions of penis releases

semen

• Prior to birth– Cell in follicle undergo mitosis and start meiosis

• Birth – Primary oocyte (2n) halted at prophase I

• Puberty– LH stimulates meiosis I completion

• Secondary oocyte (n) halted at metaphase II & polar body– Ovulation releases

• Fertilization completes meiosis• Second polar body

Oogenesis

Spermatogenesis

• Diploid cells undergo mitosis after puberty

• 1 Primary (2n) to 2 secondary spermatocytes (n)

• Secondary spermatocyte to 2 spermatids

• Completes meiosis to become sperm– Process about 10 weeks

Gametogenesis

Oogenesis• Mitotic division completed

by birth

• 1 oocyte develops, polar bodies degenerate

• 1 ovum per cycle (28 days)

Spermatogenesis• Mitotic division adolescence

till death

• 4 spermatocytes result

• Mature sperm continuously produced

Fertilization

Infertility TechnologyMale

• Sperm count low or defective– Scrotum temperature change– Sperm bank

• Impotence– Viagra– Implants (irreversible)

• Intracytoplasmic sperm injection

Female• Lack of eggs

– Implant from a donor• Risk to donor

• Failure to ovulate– Hormone injections

• Multiple pregnancies• Can’t support embryo

– Surrogate mother• In vitro fertilization

STD’s

• United States w/ highest rates (developed countries)• Bacterial and fungal– Antibiotics can cure if early; resistance– Gonorrhea, chlamydia, and syphilis– Candidiasis

• Viral– Not curable, but controllable; infect others for life– Genital herpes (most difficult), HPV, HIV

• Protozoan– Trichomoniasis

Contraception• Sterilization prevents gamete

transport• Condoms prevent pregnancy and

STD’s• Abstinence only 100%• Rhythm method is unreliable

– 3-5 day sperm survival rate• Oral contraceptives prohibit

hormonal signal to follicle – Morning after pill

• RU486 induces abortion (7 weeks)– Blocks progesterone receptors