Chapter 42-43 Animal Reproduction

Sexual vs. Asexual Reproduction offspring all have same genes no variation Sexual gametes (sperm & egg)  fertilization mixing of genes  variation

Fertilization Joining of egg & sperm external internal usually aquatic animals internal usually land animals

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

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

Reproductive Hormones LH & FSH Testosterone from testes functions sperm production 2° sexual characteristics Estrogen from ovaries egg production prepare uterus for fertilized egg testes or ovaries

Sex Hormone Control in Males Hypothalamus Pituitary Testes Body cells GnRH FSH & LH testosterone

Menstrual Cycle Hypothalamus Pituitary Ovaries Body cells GnRH LH Hypothalamus Pituitary Ovaries Body cells GnRH FSH & LH estrogen FSH egg development ovulation = egg release corpus luteum estrogen progesterone Top AP Link—Ch 42-43: Events of the Ovarian and Uterine Cycles Bottom AP Link—Ch 42-43: Menstrual Cycle Feedback lining of uterus days 7 14 21 28

Female Reproductive Cycle Endocrine System Control Feedback Female Reproductive Cycle egg matures & is released (ovulation) builds up uterus lining estrogen ovary corpus luteum progesterone FSH & LH fertilized egg (zygote) maintains uterus lining pituitary gland AP Link—Ch 41: Pregnancy Test Gonadotropin-releasing hormone Gonadotropin-releasing hormone 1 (GNRH1) is a peptide hormone responsible for the release of FSH and LH from the anterior pituitary. GNRH1 is synthesized and released by the hypothalamus. GNRH1 is considered a neurohormone, a hormone produced in a specific neural cell and released at its neural terminal. At the pituitary, GNRH1 stimulates the synthesis and secretion of the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These processes are controlled by the size and frequency of GNRH1 pulses, as well as by feedback from androgens and estrogens. Low frequency GNRH1 pulses lead to FSH release, whereas high frequency GNRH1 pulses stimulate LH release. There are differences in GNRH1 secretion between females and males. In males, GNRH1 is secreted in pulses at a constant frequency, but in females the frequency of the pulses varies during the menstrual cycle and there is a large surge of GNRH1 just before ovulation. GNRH1 secretion is pulsatile in all vertebrates, and is necessary for correct reproductive function. Thus, a single hormone, GNRH1, controls a complex process of follicular growth, ovulation, and corpus luteum maintenance in the female, and spermatogenesis in the male. Human chorionic gonadotropin Human chorionic gonadotropin (hCG) is a peptide hormone produced in pregnancy that is made by the embryo soon after conception and later by the syncytiotrophoblast (part of the placenta). Its role is to prevent the disintegration of the corpus luteum of the ovary and thereby maintain progesterone production that is critical for a pregnancy in humans. hCG may have additional functions; for instance, it is thought that hCG affects the immune tolerance of the pregnancy. The rabbit test was an early pregnancy test developed in 1927 by Bernhard Zondek and Selmar Aschheim. The original test actually used mice. The test consisted of injecting the tested woman's urine into a female rabbit, then examining the rabbit's ovaries a few days later, which would change in response to a hormone only secreted by pregnant women. The hormone, human chorionic gonadotropin (hCG), is produced during pregnancy and indicates the presence of a fertilized egg; it can be found in a pregnant woman's urine and blood. The rabbit test became a widely used bioassay (animal-based test) to test for pregnancy. The term "rabbit test" was first recorded in 1949 but became a common phrase in the English language. Xenopus frogs were also used in a similar "frog test". Modern pregnancy tests still operate on the basis of testing for the presence of the hormone hCG. Due to medical advances, use of a live animal is no longer required. It is a common misconception that the injected rabbit would die only if the woman was pregnant. This led to the phrase "the rabbit died" being used as a euphemism for a positive pregnancy test. In fact, all rabbits used for the test died, because they had to be surgically opened in order to examine the ovaries. While it was possible to do this without killing the rabbit, it was generally deemed not worth the trouble and expense. hCG yes corpus luteum pregnancy no progesterone GnRH corpus luteum breaks down progesterone drops menstruation maintains uterus lining hypothalamus

Egg Maturation in Ovary Corpus luteum produces progesterone to maintain uterine lining AP Link—Ch 42-43: Follicle/Oocyte Maturation

Fertilization

Fertilization Joining of sperm & egg sperm head enters egg AP Link—Ch 42-43: Events of Fertilization

Fertilization causes changes… yolk found at vegetal hemisphere embryo at animal hemisphere (pigmented) post fertilization, animal pole rotates to where sperm penetrates the egg—forming the gray cresent

…which sets up signal cascades to help set up the body plan. AP Link—Ch 42-43: Embryonic Assymetry

Cleavage Repeated mitotic divisions of zygote 1st step to becoming multicellular unequal divisions establishes body plan different cells receive different portions of egg cytoplasm & therefore different regulatory signals

Cleavage zygote  morula  blastula establishes future development blastocoel blastomere AP Movie—Ch 42-43: Sea Urchin Embryonic Development

AP Link—Ch 42-43: Embryonic Stem Cells AP Movie—Ch 42-43: NOVA—Stem Cells

Blood Cell Production Stem cells pluripotent cells in bone marrow produce all types of blood cells cells differentiate in bone marrow & lymph tissue Recently, researchers succeeded in isolating pluripotent stem cells and growing these cells in laboratory cultures. Purified pluripotent stem cells may soon provide an effective treatment for a number of human diseases, including leukemia. A person with leukemia has a cancerous line of the stem cells that produce leukocytes. The cancerous stem cells crowd out cells that make erythrocytes and produce an unusually high number of leukocytes, many of which are abnormal. One experimental treatment for leukemia involves removing pluripotent stem cells from a patient, destroying the bone marrow, and restocking it with noncancerous stem cells. As few as 30 of these cells can completely repopulate the bone marrow.

Gastrulation Establish 3 cell layers ectoderm mesoderm endoderm outer layers skin, nails, teeth, nerves mesoderm blood, bone & muscle endoderm inner lining digestive system ectoderm mesoderm AP Link—Ch 42-43: Gastrulation endoderm

Hox Genes found in animals to determine body plan! Chapter 19!

Hox Genes genes that control differentiation on anterior-posterior axis hedgehog v. sonic hedgehog

Hox Genes 1980s | 1995 Eric Wieschaus  for his discoveries concerning the genetic control of early embryonic development Eric Wieschaus

Human Fetal Development 4 weeks 7 weeks

Sex Determination Zygote Sperm Develop in early embryo Y Testes Ovum XY X SRY Seminiferous tubules Indifferent gonads Leydig cells X No SRY Ovaries Ovum XX (Follicles do not develop until third trimester) X Sperm Zygote

Human Fetal Development 10 weeks chorionic villus sampling—as early as week 8

Human Fetal Development amniocentesis: weeks 14-18 Human Fetal Development 12 weeks 20 weeks

Human Fetal Development The fetus just spends much of the 2nd & 3rd trimesters just growing …and doing various flip-turns & kicks inside amniotic fluid Week 20

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

Human Fetal Development 30 weeks (7.5 months)

Getting crowded in there!! 32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming AP Movie—Ch 42-43: Human Fetal Development

Hormone induction Birth positive feedback

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

The end of the journey! Any Questions!