Chapter 46 Animal Reproduction 2005-2006

Sexual & asexual reproduction offspring all have same genes (clones) ______________ Sexual gametes (sperm & egg)  fertilization mixing of genes  ___________ 2005-2006

___________________ Development of an unfertilized egg honey bees drones = males produced through parthenogenesis  haploid workers & queens = females produced from fertilized eggs  diploid Honey bee eggs hatch regardless of whether the are fertilized. The female bees--queens & workers--develop from fertilized eggs that contain 32 chromosomes. These 32 chromosomes consist of two sets of 16, one set from each parent. Hence female bees are said to be diploid in origin. The males (drones) develop from unfertilized egg which contain only one set of 16 chromosomes from their mother. Drones are thus haploid in origin This reproduction by the development of unfertilized eggs is called parthenogenesis Drones develop by parthenogenesis from unfertilized eggs that the queen produces by withholding sperm from the eggs laid in large drone cells. Drones lack stings and the structures needed for pollen collection; in the autumn they are ejected by the colony to starve, unless the colony is queenless. New drones are produced in the spring for mating. Both queens and workers are produced from fertilized eggs. Queen larvae are reared in special peanut-shaped cells and fed more of the pharyngeal gland secretions of the nurse bees (bee milk or royal jelly) than the worker larvae are. The precise mechanism for this caste differentiation is still uncertain. Although workers are similar in appearance and behavior to other female bees, they lack the structures for mating. When no queen is present to inhibit the development of their ovaries, however, workers eventually begin to lay eggs that develop into drones. queen worker drone

Different strokes… parthenogenesis in aphids sex-change in fish 2005-2006 sex-change in fish

________________ earthworms mating flat worm Having functional reproductive system of both sexes earthworms mating flat worm

Fertilization Joining of egg & sperm _____________ usually aquatic animals usually land animals 2005-2006

Development External Internal development in eggs fish & amphibians in water soft eggs= exchange across membrane birds & reptiles on land hard-shell amniotic eggs structures for exchange of food, O2 & waste sharks & some snakes live births from eggs Internal placenta exchange food & waste live birth 2005-2006

Adaptive advantages? What is the adaptive value of each type of sexual reproduction number of eggs? level of parental of care habitat? 2005-2006

Human Reproduction: Reproductive hormones ___________________ from testes Functions Prenatal development of male genitalia sperm production 2° sexual characteristics Maintenance of sex drive _______________ from ovaries functions egg production prepare uterus for fertilized egg LH & FSH testes or ovaries 2005-2006

Sex hormone control in males Hypothalamus GnRH Pituitary FSH & LH Testes testosterone Body cells 2005-2006

Male reproductive system Sperm production over ____________ produced per day! ~2.5 million released per drop! 2005-2006

Male reproductive system Testes produces sperm & hormones _____________ sac that holds testicles outside of body Epididymis where sperm mature ______________ tubes for sperm to travel from testes to penis Prostate, seminal vesicles, Cowper’s (bulbourethal) glands nutrient rich fluid to feed & protect sperm buffer to counteract acids in vagina

Male reproductive system seminiferous tubule Male reproductive system sperm spermatocytes Testes & epididymis sperm production & maturation Glands seminal vesicles, prostate, bulbourethal produce seminal fluid = nutrient-rich 2005-2006

Leydig cells are responsible for the production of testosterone. Spermatogenesis Spermatogenesis occurs within each testis in small tubules called _________________ _________________ This light micrograph shows a cross section of seminiferous tubules, blood vessels and the interstitial _______________. Leydig cells are responsible for the production of testosterone.

Spermatogenesis Mitosis and meiosis may be taking place at any time in the spermatogonia. Mitosis replenishes numbers of cells, meiosis produces actual sperm (spermatozoa) ____________ help nourish sperm cells during meiosis

Spermatogenesis 2005-2006 MEIOSIS I MEIOSIS II Epididymis Testis Germ cell (diploid) Coiled seminiferous tubules 1° spermatocyte (diploid) MEIOSIS I 2° spermatocytes (haploid) MEIOSIS II Vas deferens Spermatids (haploid) Spermatozoa Cross-section of seminiferous tubule 2005-2006

Hormonal control of sperm production LH (_______________ hormone) stimulates Leydig cells to produce testosterone FSH (___________ - stimulating hormone) and testosterone stimulate meiosis in spermatogonia to produce spermatozoa

Role of epididymis, seminal vesicles, and prostate in semen production Sperm cells were produced in seminiferous tubules, carried thru the lumen, and sent to the epididymis. They are _______ briefly in the epididymis. On sexual arousal, millions of sperm cells are moved from the epididymis into the ________________. _________________ add large volume of fluid which has a high conc. of fructose for energy for the sperm cells to swim (approx. 70% of the fluid in semen is added by the seminal vesicles.) The _________ adds more fluid: alkaline which helps the sperm survive the acidic environment in a female’s vagina.

Female reproductive system

Female reproductive system Ovaries produces eggs & hormones Uterus nurtures fetus; lining builds up each month ______________________ tubes for eggs to travel from ovaries to uterus _____________ opening to uterus, dilates 10cm (4 inches) for birthing baby Vagina birth canal for birthing baby

Female reproductive system

Menstrual cycle Starting at puberty, human females begin a hormonal cycle called the menstrual cycle. Each cycle lasts (on average) 28 days. The purpose is to time the release of an egg (ovum) for possible fertilization and later implantation into the inner lining of the uterus (____________________) The implantation must occur when the endometrium is rich with blood vessels. The breakdown of the blood vessels leads to menstrual bleeding (________________); a sign that no pregnancy has occurred

Hormones Hypothalamus Pituitary Endometrium of uterus progesterone regulatory center for the menstrual cycle. The hypothalamus produces a hormone called GnRH (gonadotrophin-releasing hormone). The target tissue of GnRH is the anterior pituitary gland, which results in the pituitary producing and secreting 2 hormones into the bloodstream: FSH and LH. The target tissues for these 2 hormones are the ovaries Hypothalamus Pituitary FSH & LH estrogen progesterone Endometrium of uterus

Effects of FSH and LH on the ovaries To increase the production and secretion of __________ by the follicle cells of the ovary Estrogen enters the bloodstream Its target tissue is the endometrium of the uterus Result is growth of lining (increase in blood vessels) Stimulates egg development in ovaries

Egg maturation in ovary A spike in levels of FSH and LH leads to ovulation (release of oocyte from the follicle) The outer ring of follicle cells begin to divide and fill in the ‘wound’ area left by ovulation which forms a ____________. The corpus luteum produces progesterone for 10-12 days after ovulation. Progesterone (hormone) ___________ the thickened endometrium If no pregnancy, the corpus luteum eventually breaks down = less estrogen and progesterone 2005-2006

LH Menstrual cycle FSH … as estrogen and progesterone levels fall, the highly vascular endometrium can no longer be maintained. The capillaries begin to rupture and menstruation begins. The drop in progesterone and estrogen also signals the _____________ to begin secreting GnRH and another menstrual cycle begins. ovulation = egg release egg development corpus luteum estrogen progesterone lining of uterus days 7 14 21 28

Oogenesis In ovaries, cells called ________ go thru mitosis repeatedly to build up numbers of cells. Then those oogonia grow into larger cells (primary oocytes) and start meiosis, but the process stops at Prophase I, until puberty. Then ____ periodically stimulates a follicle to grow and induces its primary oocyte to complete meiosis I and start meiosis II ovulation Meiosis 2 completed triggered by fertilization 2005-2006

Comparison of spermatogenesis and oogenesis Millions of sperm produced every day 4 gametes for every cell that begins meiosis Very small Occurs in testis Released during ejaculation Haploid nuclei Continues throughout all of life, starting at puberty One egg is ovulated per menstrual cycle One gamete is produced for each cell that begins meiosis (plus polar bodies) Eggs are ‘large’ Occurs in ovaries Released during ovulation Haploid nuclei Ovulation starts at puberty, occurs with each menstrual cycle, then stops at menopause

Fertilization

Fertilization Enzymes from acrosome are released at the _____________. Sperm head enters egg, plasma membranes fuse together. This initiates the ___________________. 2005-2006

Fertilization and the cortical reaction As soon as the sperm reaches the nucleus, the ________________ fuse with the cell membrane and release their enzymes to the outside, making it impermeable to any other sperm cells.

Early human embryonic development: Cleavage Fertilization triggers the zygote to start repeated mitotic divisions as it moves down the Fallopian tube toward the uterus By the time the embryo reaches the uterus, it is approx. 100 cells and is ready to implant into the endometrium of the uterus. At this point, it’s a hollow ball of cells called a ________________. 2005-2006

A few days later, the embryo imbeds itself in the uterine lining A few days later, the embryo imbeds itself in the uterine lining. At this point, a woman's body begins to secrete a pregnancy hormone known as _______. This hormone maintains production of progesterone from the ovary, a crucial factor in maintaining a pregnancy.

HCG specifics HCG = Human ____________ Gonadotrophin. It enters the bloodstream of the mother its target tissue is the ______________. HCG acts to maintain the secretory functions of this gland beyond the length of time typical of a normal menstrual cycle. The corpus luteum continues to make both estrogen and progesterone and the endometrium is maintained. Later on in pregnancy, the ________ will take over estrogen and progesterone production.

Organogenesis Umbilical blood vessels Mammalian embryo Chorion Bird embryo Amnion Yolk sac Allantois Fetal blood vessels Placenta Maternal blood vessels 2005-2006

Placenta Materials exchange across membranes 2005-2006

Role of the Placenta When fully formed, 2 fetal blood vessels within the umbilical cord carry fetal blood to the placenta. The blood is ________________ and carries waste products (_____, urea, hormones). This fetal blood exchanges materials (not blood) with the maternal bloodstream. Another fetal blood vessel returns the ‘clean’ blood to the fetus (has oxygen and __________, hormones) At no time do the 2 bloods actually mix When the corpus luteum stops producing estrogen and progesterone, the placenta starts producing and secreting them.

Role of the amniotic fluid _____________ extends all the way around the fetus The fluid within it is called amniotic fluid Several functions: Provides cushioning effect if something happens to mom’s abdomen Provides safe environment where fetus has free movement and can exercise its developing muscles and skeleton Provides ______________ stability

Human fetal development 4 weeks 7 weeks 2005-2006

Human fetal development 10 weeks 2005-2006

Human fetal development 12 weeks 20 weeks 2005-2006

Human fetal development 24 weeks (6 months; 2nd trimester) fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix 2005-2006

Human fetal development 30 weeks (7.5 months) umbilical cord 2005-2006

Getting crowded in there!! 32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming 2005-2006

Hormone induction Birth positive feedback

Birth (36 weeks) 2005-2006 Intestine Placenta Umbilical cord Wall of uterus Bladder Cervix 2005-2006 Vagina

The end of the journey!