Bellwork

•Why do you think sex (exchange of gametes) has evolved? In what conditions do you think organisms would favor asexual versus sexual reproduction, and visa versa?

•Something to think about: Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction

Fig. 46-3

Asexual reproduction

Female

Sexual reproduction

Female

Generation 1

Male

Generation 2

Generation 3

Generation 4

•Sexual reproduction results in genetic recombination, which provides potential advantages:▫Increase in variation in offspring

increase in the reproductive success in changing environments

An increase in the rate of adaptation A shuffling of genes and the elimination of

harmful genes from a population

•Sexual reproduction is the creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote

•Asexual reproduction is creation of offspring without the fusion of egg and sperm

Asexual

•In budding, new individuals arise from outgrowths of existing ones

•Fragmentation is breaking of the body into pieces, some or all of which develop into adults▫Fragmentation must be accompanied by

regeneration, regrowth of lost body parts•Parthenogenesis is the development of a

new individual from an unfertilized egg

Human Reproductive system

Fig. 46-10

Oviduct

Ovary

Uterus(Urinary bladder)(Pubic bone)Urethra

(Rectum)Cervix

Vagina ShaftGlansPrepuce

Clitoris

Labia minoraLabia majora

Vaginal opening

Ovaries

Uterus

Follicles

Oviduct

Cervix

Corpus luteumUterine wall

Endometrium

Vagina

•Each ovary contains many follicles, which consist of a partially developed egg (oocyte)

•Once a month, an oocyte develops into an ovum (egg) by the process of oogenesis

•Ovulation expels an egg cell from the follicle

•The egg cell travels from the ovary to the uterus via an oviduct, or fallopian tube

•Cilia in the oviduct convey the egg to the uterus, also called the womb

Fig. 46-11

Seminalvesicle(behind bladder)

(Urinarybladder) Prostate

glandBulbourethralglandErectile tissueof penis

Urethra

ScrotumVas deferensEpididymis

Testis

Seminal vesicle

(Urinarybladder)

(Urinaryduct)

(Rectum)Vas deferens

Ejaculatory ductProstate gland

Bulbourethral gland Vas deferens Epididymis

TestisScrotum

(Pubic bone)

Erectiletissue

Urethra

Glans

Prepuce

Penis

•The male gonads, or testes, consist of highly coiled tubes surrounded by connective tissue

•Sperm form in these seminiferous tubules

•Production of normal sperm cannot occur at the body temperatures of most mammals

•Semen is composed of sperm plus secretions from three sets of accessory glands• The two seminal vesicles contribute about 60%

of the total volume of semen▫Contains fructose providing energy for the sperm

and coagulating enzymes• The prostate gland secretes its products

directly into the urethra through several small ducts▫Contains anticoagulant and citrate (sperm

nutrient)• The bulbourethral glands secrete a clear mucus

before ejaculation that neutralizes acidic urine remaining in the urethra ▫As well as some semen – this is why the withdrawal

method of birth control is very ineffective

Fig. 46-11b

Seminal vesicle

(Rectum)

Vas deferens

Ejaculatory duct

Prostate gland

Bulbourethral gland Vas

deferensEpididymisTestisScrotum

(Urinarybladder)

(Urinaryduct)

(Pubic bone)

Erectiletissue

UrethraGlans

Prepuce

Penis

•Gametogenesis, the production of gametes by meiosis, differs in females and males

•Sperm are small and motile and are produced throughout the life of a sexually mature male

•Spermatogenesis is production of mature sperm

Fig. 46-12aEpididymis

Seminiferous tubule

Testis

Cross sectionof seminiferoustubule

Sertoli cellnucleus

Primordial germ cell in embryo

Mitotic divisions

Spermatogonialstem cell

Mitotic divisions

Mitotic divisions

Spermatogonium

Primary spermatocyte

Meiosis I

Meiosis II

Secondary spermatocyteLumen ofseminiferous tubule

Plasma membrane

Tail

Neck

Midpiece

Head

Mitochondria

Nucleus

Acrosome

Spermatids(at two stages ofdifferentiation)

Earlyspermatid

Differentiation(Sertoli cellsprovide nutrients)

Sperm

2n

2n

2n

n n

n n n n

n n n n

•Eggs contain stored nutrients and are much larger

•Oogenesis is development of mature oocytes (eggs) and can take many years

Fig. 46-12e

Ovary

In embryo

Primordial germ cell

Mitotic divisions

Oogonium

Mitotic divisions

Primary oocyte(present at birth), arrestedin prophase of meiosis I

Firstpolarbody

Completion of meiosis I and onset of meiosis II

Secondary oocyte,arrested at metaphase of meiosis II

Ovulation, sperm entry

Completion of meiosis IISecon

dpolarbody Fertilized egg

Primaryoocytewithinfollicle

Growingfollicle

Mature follicle

Rupturedfollicle

Ovulatedsecondary oocyte

Corpus luteum

Degeneratingcorpus luteum

2n

2n

nn

n

n

Sex Hormones

•FSH and LH regulate processes in the gonads and the production of sex hormones

•The sex hormones are androgens, estrogens, and progesterone

•Females – mainly estrogens and progestrone•Male – mainly androgens (testosterone)

Male Hormones•FSH and LH regulate cells which control

sperm production

Female Hormones

•In females, the secretion of hormones and the reproductive events they regulate are cyclic

Fertilization

•Sperm can live up to 5 days in the reproductive tract

•The Egg can live 24-48 hours after being released

• Conception, fertilization of an egg by a sperm, occurs in the oviduct

• The resulting zygote begins to divide by mitosis in a process called cleavage

• Division of cells gives rise to a blastocyst, a ball of cells with a cavity

•The embryo releases human chorionic gonadotropin (hCG), which prevents menstruation▫This is what pregnancy tests detect

First trimester

•Embryo gets nutrients from the endometrium▫Diffuses nutrient, immune protection,

respiratory gasses and releases waste▫Splitting of the embryo can develop into

monozygotic twins (genetically identicle) Dizygotic twins – two eggs fertilized

independently▫Organogenesis – development of body

organs

Second trimester

•Placenta takes over hormone levels (progesterone)

Third trimester

•Growth of the fetus