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Reproduction Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Asexual and Sexual Reproduction In asexual reproduction, the offspring are genetically identical to one parent The process begins with mitosis Protists typically divide by fission Cnidarians typically divide by budding Fig. 1 Asexual reproduction in Euglena Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 1 Asexual and Sexual Reproduction In sexual reproduction, a new individual is formed by the union of two gametes (egg and sperm) A zygote is formed Develops by mitosis into a multicellular organism Haploid gametes are produced in the gonads Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Different Approaches to Sex Parthenogenesis Offspring are produced from unfertilized eggs Common among arthropods Some are exclusive Others switch! Common also in some lizard species Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hermaphroditism Hamlet bass One individual has both testes and ovaries Tapeworms and earthworms Hermaphroditism may be sequential Switch sexual roles! Switch sexes! Fig. 2 Individuals change sex Protogyny From female to male Protandry From male to female Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Bluehead wrasse Sex Determination In some reptiles, sex is determined by environmental changes In mammals, it is determined early in embryonic development Embryonic gonads are indifferent Y chromosome converts them to testes Responsible gene is SRY Sex-determining region of the Y chromosome Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 3 Sex determination Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 2 Evolution of Reproduction Among the Vertebrates Vertebrate sexual reproduction evolved in the ocean before vertebrates colonized land Most marine bony fish use external fertilization Male and female gametes are released into the water where fertilization occurs Most other vertebrates use internal fertilization Male gametes are introduced into the female reproductive tract Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display There are three strategies for internal fertilization 1. Oviparity Fertilized eggs are deposited outside mother’s body to complete their development 2. Ovoviviparity Fertilized eggs are retained within the mother to complete their development Young obtain nourishment from egg yolk 3. Viviparity Fertilized eggs are retained within the mother to complete their development Young obtain nourishment from mother’s blood Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fish and Amphibians The eggs of most bony fish are fertilized externally Eggs contain little yolk Young fish must seek its food from the water surrounding it Thousands of eggs are fertilized, but only a few of resulting individuals reach maturity Fertilization in most cartilaginous fish is internal Development of young is viviparous Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fertilization is external in most amphibians Fig. 6 Eggs of most species develop in water Poison arrow frog With some Male! interesting exceptions South American marsupial frog Female Fig. 7 Development is divided into embryonic, larval and adult stages Surinam frog Darwin’s frog Female Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Male! Reptiles and Birds Most reptiles are oviparous, laying amniotic eggs Other species are ovoviviparous or viviparous Fig. 8 How turtles do it Most male reptiles use a penis to inject sperm into females This process is called copulation Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display All birds are oviparous, laying amniotic eggs As egg passes along oviduct, glands secrete albumin proteins and the hard calcareous shell Fig. 9 Birds are homeotherms Incubate eggs to keep them warm Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mammals Some mammals are seasonal breeders Others have reproductive cycles Periodic release of a mature ovum (ovulation) Most female mammals have estrous cycles Females sexually receptive to males only around time of ovulation (estrus) Apes and humans have menstrual cycles Females bleed when shedding inner lining of the uterus Can copulate at any time in their cycle Cats and rabbits are induced ovulators Ovulation only after copulation due to LH secretion Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Three types of mammals Monotremes are oviparous Lay eggs Young hatchlings obtain milk by licking mammary glands (they lack nipples) Marsupials are viviparous Give birth to incompletely developed fetuses Complete development in mother’s pouch Obtain food from nipples in mammary glands Placentals are viviparous Retain young in uterus for long periods of development Fetuses are nourished by the placenta Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 10 Reproduction in mammals Duck-billed platypus Kangaroo Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Deer Review the Concepts What are gametes? Sex is determine by which chromosomes? What is the union of the sperm and egg called? Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 3 Males Fig. 11 The male reproductive organs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The testis produces sperm and testosterone Enclosed in a hanging sac called the scrotum Sperm need cooler temperature to develop Spermatogenesis occurs in the seminiferous tubules Sperm are then transferred to the epididymis for storage and maturation From there to the vas deferens To the urethra which empties through the penis Contains 23 chromosomes Fig. 13 Human sperm cell Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 12 The testis and formation of sperm Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The penis contains long cylinders of spongy tissue These get filled with blood causing an erection Physical stimulation is required for ejaculation 2-5 milliliters of semen are ejected Fig. 14 This volume contains several hundred million sperm Plus secretions from the prostate and other glands Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 4 Females Fig. 15 The female reproductive organs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display At birth, a female’s ovaries contains all the oocytes she will ever produce ~ 2 million oocytes are arrested in prophase I of the first meiotic division At puberty, the release of FSH causes the resumption of meiosis I in a few oocytes However, only one becomes dominant and is ovulated Mature egg cells are called ova (singular, ovum) This cycle is repeated about every 28 days Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 16 The ovary and formation of an ovum Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fertilization of the egg occurs high in the Fallopian tubes (also called uterine tubes or oviducts) The fertilized egg is now called a zygote It is transported to the uterus A muscular pear-shaped organ about the size of a fist It narrows to a muscular ring called the cervix Leads to the vagina Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Review the Concepts Name the male and female reproductive organs. Name the two things produced by the testes. Where does spermatogenesis occurs In which stage are the oocytes arrested? How often does ovulation occurs? Where does fertilization occurs? Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 17 A comparison of mammalian uteruses Primates Cats, dogs and cows Rats, mice and rabbits Marsupials, such as opossums, have two unconnected horns, two cervices and two vaginas Male marsupials have a forked penis! Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The fertilized egg is pushed down the oviducts by the rhythmic contraction of its smooth muscles The journey takes 5-7 days The uterus is lined with a stratified epithelial membrane called the endometrium The zygote attaches to this layer and begins embryonic development! If the egg is not fertilized, the surface layer of the endometrium is shed during menstruation The underlying layer generates a new surface layer during the next cycle Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 5 Hormones Coordinate the Reproductive Cycle The female reproductive cycle is composed of two distinct phases Follicular phase Egg reaches maturation and is ovulated Luteal phase Body continues to prepare for pregnancy A family of hormones coordinates these two phases Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Follicular Phase Development of the egg within the ovary The oocyte and its surrounding mass of tissue is called the follicle FSH secretion triggers the maturation of several follicles and resumption of meiosis in their oocytes But only one achieves full maturity FSH also causes the ovary to secrete estrogen Negative feedback by estrogen, causes the hypothalamus to stop the pituitary’s FSH output Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Luteal Phase The body is prepared for fertilization Hypothalamus causes the anterior pituitary to begins secreting luteinizing hormone (LH) LH inhibits further estrogen production It also causes the wall of the follicles to burst Oocyte is ovulated into oviducts LH directs the repair of the ruptured follicle, which becomes the corpus luteum Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 18 The human menstrual cycle Levels of gonadotropic hormones in blood Pituitary gland LH FSH FSH 0 7 14 21 28 days Ovarian cycle Developing follicles Ovulation Corpus luteum Luteal phase Hormone blood levels Estradiol Progesterone 0 7 14 21 28 days Endometrial changes during menstrual cycle Menstrual phase 0 Proliferative phase 7 Ovulation 14 Secretory phase 21 28 days Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Luteal Phase The corpus luteum begins to secrete the hormone progesterone Progesterone inhibits FSH It also thickens the endometrium preparing for fertilization If fertilization does not occur, progesterone production stops and the luteal phase ends Thickened endometrial layer sloughs off This causes the bleeding associated with menstruation Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fig. 18 The human menstrual cycle Levels of gonadotropic hormones in blood Pituitary gland LH FSH FSH 0 7 14 21 28 days Ovarian cycle Developing follicles Ovulation Corpus luteum Luteal regression Luteal phase Hormone blood levels Estradiol Progesterone 0 7 14 21 28 days Endometrial changes during menstrual cycle Menstrual phase 0 Proliferative phase 7 Ovulation 14 Secretory phase 21 Menstrual phase 28 days Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Luteal Phase If fertilization does occur, the corpus luteum is maintained by human chorionic gonadotropin (hCG) hCG is a hormone produced by the embryo It is tested for in all pregnancy tests Two other hormones are of importance Prolactin Stimulates milk production Oxytocin Initiates milk release Induces labor Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Review the Concepts What are the two phase of the female reproductive cycle? List the events of the Follicular phase. List the events of the Luteal phase. List the hormones involved in the Follicular phase List the hormones involved in the Luteal phase Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 6 Embryonic Development The vertebrate embryo develops in three stages Cleavage A hollow ball of cell forms Gastrulation Cells move to the interior, forming the primary tissues Neurulation The organs of the body form Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cleavage: Setting the Stage for Development During cleavage, zygote rapidly divides into larger and larger numbers of smaller and smaller cells A morula forms A tightly packed mass of about 32 blastomeres Further division results in a hollow ball of 5002,000 cells called the blastocyst Contains a fluid-filled cavity, the blastocoel Inner cell mass Forms the embryo Trophoblast Becomes the placenta Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cleavage: Setting the Stage for Development Embryo reaches the uterus on day 6 It penetrates the endometrial lining Initiates membrane formation Amnion Encloses embryo Chorion Forms from the trophoblast Interacts with uterine tissue to form the placenta Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Gastrulation: Onset of Developmental Change Certain groups of cells move inwards from the inner cell mass at about 10-11 days after fertilization This process of gastrulation results in the three primary germ layers Endoderm Ectoderm Mesoderm Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Review the Concepts List the three stages of the vertebrate embryo development. List the three primary germ cells and their functions. Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Neurulation: Determination of Body Architecture In the third week, the three primary germ layers begin development into body tissues and organs First, the notochord develops from the mesoderm The neural tube develops from the ectoderm The gut develops from the endoderm On either side of the notochord blocks of tissue form These somites give rise to muscles, vertebrae and connective tissues developing notochord By the end of the third week, the embryo is about 2 mm (< 0.1 inches) long Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Fetal Development Fourth week Formation of body organs, or organogenesis Critical time in development Fig. 20a Alcohol use may cause fetal alcohol syndrome Embryo reaches about 5 mm Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Fetal Development Second month Great changes in morphology occur Limbs assume adult shape Major internal organs are evident Embryo reaches about 25 mm Fig. 20b Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Fetal Development Third month Development is essentially complete except for lungs and brain Fig. 20c Developing human is now called a fetus It carries out primitive reflexes like sucking Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Fetal Development Second trimester A time of growth Bone formation occurs Hair and body are covered with fine hair called lanugo By the end of the 6th month, the fetus is 30 cm (1 foot) long Fig. 20d Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7 Fetal Development Third trimester Pace of growth accelerates Weight of fetus more than doubles Nutrients provided by mother’s blood via the placenta Fig. 21 Most major nerve tracts are formed in the brain Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Postnatal development Babies typically double birth weight within a few months Different body parts grow at different rates Allometric growth Nerve cells produced at an average rate of > 250,000 per minute At 6 months, neuron production ceases permanently Fig. 22 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 8 Sexually Transmitted Diseases and Contraception Sexually transmitted diseases are transmitted during sexual intercourse or sexual activities Contraception, or birth control, is the prevention of pregnancy Several different methods are available These differ in their effectiveness and acceptability to different couples Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sexually Transmitted Diseases STDs are diseases that are spread from one person to another through sexual contact They include Acquired Immune Deficiency Syndrome (AIDS) Caused by the human immunodeficiency virus (HIV) Gonorrhea Caused by the bacterium Neisseria gonorrhoeae Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sexually Transmitted Diseases Chlamydia Caused by the bacterium Chlamydia trachomatis Syphilis Caused by the bacterium Treponema pallidum Genital Herpes Caused by the herpes simplex virus type 2 (HSV-2) Most common STD in the US Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Birth Control Abstinence Simplest and most reliable way Natural family planning, or the rhythm method Prevention of egg maturation Birth-control pills Estrogen and progesterone Shut down production of the pituitary hormones FSH and LH Birth-control injections Birth-control patches The Ring Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Birth Control (cont.) Prevention of embryo implantation Intrauterine devices (IUDs) RU486 (“morning after pill”) Sperm blockage Condoms Diaphragms Sperm destruction Spermicidal jellies Foams Sterilization Vasectomy in males Tubal ligation in females Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Effectiveness of Contraceptives Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Review the Concepts List some of the most common STD’s Which is the most effective method of contraception? Which is the least effective method of contraception? Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display