Bio exam 4 Chapter 49

Gonads

eiher ovaries or testes They have a DUAL function in mammals as they do in all verts: they both produce GAMETES and secrete HORMONES that are responsible for sexual development and mating behavior Males have ducts that carry sperm from the testes to the exterior Females have an OVIDUCT that leads from each ovary to the uterus, in which fertilized eggs implant and proceed through embryonic development. Nutrients from the mother and wastes from the embryo are exchanged through the placenta. After birth, the newborn offspring is nourished w/ milk secreted by the mom's mammary glands

oviparity viviparity ovoviparity

3 major types of internal fertilization support for embryonic development:

Budding

A new individual grows and develops while attached to the parent Ex: sponges, tunicates, and some cnidarians The offspring may break free from the parent, or remain attached to form a colony In the cnidarian Hydra, an offspring buds and grows from one side of the parent's body and then detaches to become a separate individual

Asexual Reproduction

A single individual gives rise to offspring w/o fusion of gametes (egg and sperm) NO genetic input from another individual Aquatic inverts and some terrestrial annelids and insects It is rare among verts One or many cells of a parent develop directly into a new individual In some, the cells taking part are genetically VARIED products of meiosis, BUT in most, they are the products of mitosis Offspring are genetically identical to one another and to the parent Genetic CLONES of the parent Asexual reproduction of this kind is also called clonal reproduction Genetic uniformity of offspring can be advantageous in environments that remain stable and uniform Asexual reproduction preserves gene combinations, producing individuals that are successful in such environments Individuals do NOT have to expend energy to produce gametes or find a mate It can also bring reproductive advantages to individuals living in sparsely populated areas, or to sessile animals which can't move from place to place Mechanisms Involving MITOSIS: fission, budding, and fragmentation

oviducts and sperm ducts external accessory sex organs participate in the delivery

Egg and sperm are delivered from ovaries and testes to the site of fertilization by ____ in females and _____ in males

sperm and egg activates the EGG

Fertilization involves fusion of a ____ and ____ which activates the ____ for development Once sperm touches the outer surface of an egg of the same species, receptor proteins in the sperm plasma membrane bind the sperm to the vitelline coat or zona pellucida Only a sperm from the same species as the egg can recognize and bind to the egg surface Species recognition is highly important in animals that carry out eternal fertilization b/c the water surrounding the egg may contain sperm of many different species It is less important in internal fertilization b/c structural adaptations and behavioral patterns of mating usually limit sperm transfer form males to females of the same species

Germ cells: a cell line that is set aside early in embryonic development and remains distinct from the other somatic cells of the body During development, the germ cells collect in specialized gamete-producing organs, the gonads- the testes in males and ovaries in females In some animals, the germ cells also give rise to families of cells that assist gamete development

Gametes in animals form from what type of cells?

MEIOSIS

Gametogenesis involves the coordination of _____ and sperm and egg development

variation

Hermaphroditism is a ____ on sexual reproduction

The non-motile eggs move through the oviducts on currents generated by the beating of cilia longing the oviducts, or by contractions of the oviducts or the body wall

How do eggs move through the oviducts?

The slow block to polyspermy occurs in many organisms, including mammals. The fusion of egg and sperm triggers an increase in Ca2+ ions in the cytosol. The Ca2+ ions activate proteins that initiate a high level of metabolic activity in the egg. The released calcium ions also cause the cortical granules to fuse w/ the plasma membrane of the egg and release their contents to the outside. Enzymes released from the granules alter the egg coats in a matter of minutes after fertilization, and this blocks further sperm from attaching to and penetrating the egg.

How is the slow block to polyspermy brought about?

Female Sexual organ function

Human females have a pair of ovaries suspended in the abdominal cavity An oviduct leads from each ovary to the uterus, which is a hollow, saclike organ w/ walls containing smooth muscle. The uterus is lined by the endometrium, which is formed by layers of connective tissue w/ embedded glands and is richly supplied w/ blood vessels. If an egg is fertilized and begins development, it must IMPLANT in the endometrium to continue developing. The lower end of the uterus, the cervix, opens into a muscular canal, the vagina, which leads to the exterior Sperm enter the female reproductive tract via the vagina and, at birth the baby passes from the uterus to the outside through the vagina At birth of a female, each of her ovaries contain about 1 mil. Oocytes, arrested at the end of the first meiotic prophase Of these oocytes, about 200,000 to 400,000 survive until a female becomes sexually mature; about 400 are ovulated-released into the oviducts as immature eggs - during the lifetime of a woman Egg is released into the abdominal cavity and is pulled into the nearby oviduct by the current produced by the beating of the cilia lining the oviduct. The cilia also propel the egg through the oviduct and into the uterus. Fertilization of the egg occurs in the OVIDUCT External female sex organs, collectively called the vulva, surround the opening of the vagina. Two folds of tissue the labia minora, run from the front to rear on either side of the opening to the vagina These folds are partially covered by a pair of fleshy, fat-padded folds, the labia majora, which also run from front to rear on either side of the vagina At the anterior end of the vulva, the labia minora join to partly cover the head of the clitoris. The rest of the clit is within the body The clit contains erectile tissue and has the same embryonic origins as the penis A pair of greater vestibular glands, with openings near the entrance of the vagina, secretes a mucus-rich fluid that lubricates the vulva The opening of the urethra, which conducts urine form the bladder, is located btw. The clit and the vaginal opening Most nerve endings associated w/ erotic sensations are conc. In the clit, in the labia minora, and around the opening of the vagina When a human female is born, a thin flap of tissue, the hymen, partially covers the opening of the vagina This membrane, if it has not already been ruptured by physical exercise or other disturbances, is broken by the first sexual intercourse

eutherian

Human reproduction is typical of that of ______ (placental) mammals

Parthenogenesis

Offspring can be produced by the growth and development of an egg w/o fertilization The offspring may be haploid or diploid depending on the species The egg derives from meiosis in the female parent, the offspring are NOT genetically identical to the parent or to each other Occurs in some inverts (aphids, bees, and water fleas) Ex: in water fleas: the female produces two types of eggs One egg develops ONLY if fertilized the other develops by _______ also occurs in some verts. Ex: in certain fish, salamanders, amphibians, lizards, and turkeys An egg produced by meiosis, typically doubles its chromosomes to produce a diploid cell that begins development In single-sex species where females have two identical sex chromosomes, the offspring are female, whereas in single-sex species where males have two identical sex chromosomes, the offspring are male Ex: whiptail lizards are females, produced solely by __________ These females go through the motions of mating and copulation w/ each other

Produces mature HAPLOID egg cells called ova (aka EGGS) NON-motile cells that are larger than sperm of the same species Only one of the cell products of meiosis develops into a functional egg The egg retains almost all of the cytoplasm of the parent cell The other products form nonfunctional cells called POLAR bodies The UNEQUAL cytoplasmic divisions concentrate nutrients and other molecules required for development in the egg Polar bodies disintegrate eventually and do not contribute to fertilization or embryonic development Oocytes DO NOT complete meiosis until fertilization In mammals, oocytes STOP developing at the END of the FIRSR MEIOTIC prophase w/in a few weeks after a female is born Oocytes remain in the ovary at this stage of development until the female is sexually mature Then, one to several oocytes advance to the METAPHASE of the SECOND MEIOTIC division and are RELEASED from the ovary at intervals ranging from days to months, or at certain seasons, depending on the species (in humans, oocytes remain in prophase of the first meiotic division for perhaps 50 years until menopause) Meiosis is completed at fertilization to produce the fully mature egg An egg has specialized features: 1) Stored nutrients and cytoplasmic determinants required for at least the early stages of embryonic development 2) egg coats of one or more kinds that protect the egg from mechanical injury and infection and, in some species, protect the embryo after fertilization 3) mechanisms that prevent the egg from being fertilized by more than one sperm cell The amount of stored nutrients in an egg varies w/ the animal Mammalian eggs are microscopic, containing few stored nutrients The embryo develops inside the mother and is supplied w/ nutrients by the mother's body The relatively large eggs of birds and reptiles contain all the nutrients required for compete embryonic development: Yolk contains the egg cell White contains the nutrients No matter what the size of an animal egg, however, most of the volume is CYTOPLASM, and the egg nucleus is microscopic or nearly so in all species Egg coats are surface layers added DURING oocyte development or fertilization in many species Vitelline coat, called the zona pellucida in mammals is a gel-like matrix of proteins, glycoproteins, or polysaccharides located immediately outside the plasma membrane of the egg cell Insect eggs have additional outer protein coats that form a hard, water-impermeable layer for preventing desiccation Amphibians and some echinoderms have an additional outer egg jelly layer instead of a tough protein coat that protects the egg from drying out In birds, reptiles and one group of egg-laying mammals, the monotremes, the egg white, a thick solution of proteins, surrounds the vitelline coat. Outside the white is the shell of the egg, flexible and leathery in reptiles and mineralized and brittle in birds BOTH the EGG WHITW and the SHELL are added while the egg- fertilized or not- is in transit through the OVIDUCT, the tube through which the egg moves from the ovary to the outside of the body In mammals, the egg is surrounded by FOLLICLE cells during its development These cells, which grow from ovarian tissue, nourish the developing egg They also make up part of the zona pellucida while the egg is in the ovary, and remain as a protective layer after it is released

Oogenesis

monthly

Ovulation occurs in a _____ cycle Reproduction in human females is under neuroendocrine control, involving complex interactions btw. The hypothalamus, pituitary, ovaries, and uterus Under this control, approx.. every 28 days from puberty to menopause, a female releases an egg from one of her ovaries The cyclic events in the ovary leading to ovulation are known as the ovarian cycle This cycle is coordinated w/ the uterine cycle, or menstrual cycle, events in the uterus prepare it to receive the egg if fertilization occurs.

Fission

Parent separates into two or more offspring of approximately equal size Ex: planarians (flatworms) reproduce by fission and may divide by transverse or longitudinal fission

Fragmentation

Pieces separate from the body of a parent and develop (regenerate) into new individuals Many species of cnidarians, flatworms, and annelids, and some echinoderms can reproduce by this method

diversity

Sexual reproduction generates ______ among offspring

Produces mature, HAPLOID sperm cells, also called spermatozoa (aka SPERM) Sperm are motile cells, driven through a watery medium by the whip-like beating of a flagellum that extends from the posterior end of the cell (fig 49.4) Maturing from spermatic to sperm, most of the cytoplasm is LOST, EXCEPT for mitochondria, which surround the base of a flagellum Mitochondria produce ATP used as the energy source for flagellar beating At the head of the sperm, a specialized secretory vesicle, the acrosome, forms a cap over the nucleus It contains enzymes and other proteins that help the sperm attach to and penetrate the surface coatings of an egg of the same species All FOUR products of meiosis develop into functional sperm

Spermatogenesis

Ovarian Cycle

This cycle produces a mature egg The starting point for the cycle is a primary oocyte in prophase of meiosis division I. The beginning of the cycle is triggered by an increase in the release of gonadotropin-releasing hormone (GnRH) by the HYPOTHALAMUS This hormone stimulates the pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH) into the bloodstream FSH stimulates 6-20 primary oocytes in the ovaries to be released from prophase of meiosis I and continue through the meiotic divisions As primary oocytes develop into secondary oocytes - which arrest in metaphase of meiosis II- they become surrounded by cells that form a follicle (day 2 of the cycle) During this follicular phase, the follicle grows and develops and at its largest size, becomes filled w/ fluid and may reach 12-15 mm in diameter Usually ONLY ONE follicle develops into maturity w/ release of the eggs (secondary oocyte) by ovulation If two or more follicles develop and their eggs are ovulated, multiple births of non-identical siblings can result As the follicle enlarges, FSH and LH interact to stimulate the follicular cells to secrete estrogens (female sex hormone), primarily estradiol Initially the estrogens are secreted in low amounts; at this level, at this level, the estrogens have a NEGATIVE feedback effect on the pituitary, inhibiting its secretion of FSH Result = FSH secretion declines briefly, estrogen secretion increases steadily and its level peaks at about 12 days after follicle development begins High estrogen level now has a POSITIVE feedback effect on the hypothalamus and pit. Increasing the release of GnRH and stimulating the pit. To release a burst of FSH and LH Increased estrogen levels also convert the mucus secreted by the uterus to at thin and watery consistency, making it easier for sperm to swim through the uterus Burst in LH secretion stimulates the follicle cells to release enzymes that digest away the wall of the follicle, causing it to burst and release the egg ; this is ovulation LH also initiates the last phase of the menstrual cycle, the luteal phase LH causes the follicle cells remaining at the surface of the ovary to grow into an enlarged, yellowish structure, the corpus luteum Acting as an endocrine gland, the corpus luteum secretes several hormones; estrogens, large quantities of progesterone, and inhibin Progesterone, a female sex hormone, stimulates growth of the uterine lining and inhibits contractions of the uterus BOTH progesterone and inhibin have a negative feedback effect on the hypothalamus and pit. Progesterone inhibits the secretion of GnRH W/o it, the pit. Does NOT release FSH and LH FSH secretion from the pit. Is also inhibited directly by inhibin Fall in FSH and LH levels diminishes the signal for follicular growth, and no new follicles begins to grow in the ovary If fertilization does NOT occur, the corpus luteum gradually degenerates as cells are destroyed by phagocytosis and blood supply is cut off By 10 days after ovulation, little tissue remains, meaning that estrogen, progesterone, and inhibin are no longer secreted In the absence of progesterone, menstruation begins As progesterone and inhibin levels decrease, FSH and LH secretion is no longer inhibited, and a new monthly cycle begins

Fertilization

the union of gametes that initiates the development of a new individual Sea urchins are a well-studied organism for invertebrate development and reproduction and often-used model for human fertility research The steps are similar in other organisms The attachment of sperm to egg triggers a rapid series of events starting w/ acrosomal reaction, enzymes in the acrosome are released from the sperm and digest a path through the egg coats The sperm, follows the path (w/ a beating tail) until its plasma membrane touches and fuses w/ plasma membrane of the egg Fusion introduces the sperm nucleus into the egg cytoplasm and activates the egg to complete meiosis and begin development

Asexual and sexual reproduction

what are the two basic modes of reproduction in the animal kingdom?

Egg coats are surface coats around the egg. They are added during oocyte development or fertilization. Egg coats provide protection against mechanical injury, infection by microorganisms, and in some species, loss of water. Mammalian eggs have an egg coat called the ZONA PELLUCIDA immediately surrounding the egg. This gel-like coating is called the vitelline coat in other organisms In BIRBS, a thick solution of proteins - the egg white- surrounds a vitelline coat. Bounding the egg white is a hard shell

1) What are egg coats, and what is their function? What egg coats do mammalian and bird eggs have?

Ovoviparous

Animals RETAIN fertilized eggs w/in the body and the embryo develops using the nutrients provided by the egg There is NO uterus or placenta When development is complete, the eggs hatch inside the mother and the offspring are released to the exterior Ex: fishes, lizards, amphibians, snakes, and many inverts

Viviparous

Animals RETAIN the embryo w/in the mother's body and nourish it during at least early embryo development All mammals EXCEPT the monotremes Seen also in all other vertebrate groups except crocs, turtles, and birds Development of the embryo takes place in a specialized saclike organ, the uterus (womb) The placental mammals or eutherians, have a specialized temporary structure, the placenta, which connects the embryo to the uterus Placenta facilitates the transfer of nutrients from the blood of the mother to the embryo and the movement of wastes to the opposite direction Ex: humans Nonplacental mammals: Ex: marsupials or metatherians b/c of a belief that they lacks a placenta BUT they do have placenta, it derives from a different tissue than that of eutherians and DOES NOT CONNECT the embryo and the uterus It provides nutrients to the embryo from an attached membranous sac containing yolk for only the early stages of its development The embryo is then born at an EARLY stage and crawls over the mother's fur to reach the marsupium, an abdominal pouch w/in which it attaches to nipples and continues its development Kangaroos, koalas, wombats, and opossums are marsupials

Hermaphroditism

BOTH mature egg-producing and mature sperm producing tissue is present in the same individual Ex: flatworms, earthworms, land snails, etc. inverts Rare cases in humans and other mammals where someone has both testicular and ovarian tissues NOT TRUE hermaphrodites b/c they are not both male and female, BUT rather genetically either male or female but w/ ambiguous genitalia Best to be called pseudohermaphrodites rather than true hermaphrodites Most hermaphroditic animals do not fertilize themselves, b/c anatomical barriers prevent individual from inducing sperm into their own body, or the egg and sperm mature at DIFFERENT times Prevention of self-fertilization maintains the genetic variability of sexual reproduction 2 forms of hermaphroditism: Simultaneous Hermaphroditism: Individuals develop functional ovaries and testes at the SAME time Sequential Hermaphroditism: Individuals change from one sex to the other Ex: Earthworms provide a common example of simultaneous hermaphroditism Only known vertebrae simultaneous hermaphrodites are hamlets, a group of predatory sea basses Sequential hermaphroditism is seen in some inverts (slipper shell) and some ectothermic verts (fishes: clownfish) NEMO In some species, the initial sex is male (as with the slipper shell and the clownfish) and in others it is female

REDUCES

Meiosis ______ the number of chromosomes for the diploid level characteristic of somatic cells of the species, in which there are two copies of each chromosome, to the haploid cells of the species in which there is only ONE copy of each chromosome fusion of haploid sperm and egg DURING fertilization RESTORES the DIPLOID number of chromosomes and produces a ZYGOTE, the first cell of a NEW individual

Oviparous

Lay eggs that contain the nutrients needed for development of the embryo outside the mother's body Ex: spider, insects, most reptiles and birds Monotremes (the only oviparous mammal): the echidnas and the duck-billed platypus

Sexual Reproduction

Male and female parents produce offspring through the union of egg and sperm generated by meiosis Animals reproduce sexually by the union of sperm and eggs produced by meiosis Advantage of sexual reproduction is the generation of GENETIC DIVERSITY among offspring This diversity increases the chance that, in a changing environment, at least some offspring will grow and reproduce successfully Diversity increases the chance that offspring may be able to live and reproduce in environments previously unoccupied by the species 2 mechanisms part of meiosis give rise to the genetic diversity in eggs and sperm: Genetic recombination: Mixes alleles of parents into new combinations w/in chromosomes Independent assortment of chromosomes: Results in random combinations of maternal and paternal chromosomes in gamete nuclei Additional variability is generated at fertilization when eggs and sperm from genetically different individuals fuse together at random to initiate the development of new individuals To these sources of variability are added random DNA mutations, which are the ULIMATE SOURCE of variability for both sexual and asexual reproduction DISADVANTAGES of sexual reproduction: Expenditure of energy and raw materials in producing gametes and finding mates and producing fewer offspring per parent (there is one set of offspring per two parents rather than one set of offspring per parent as in asexual reproduction) The need to find mates can expose animals to predation and takes time from finding food and shelter and caring for existing offspring Concerning offspring number, consider a female that reproduces asexually. All her progeny will be females, each of whom will produce more offspring by asexual reproduction HOWEVER, in sexual reproduction, ½ of the offspring of a mating pair are females, and ½ are males Therefore, only ½ of the progeny produced by sexual reproduction of a female produce offspring for the following generation

sexual reproduction occurs when there is environmental STRESS, asexual reproduction occurs under FAVORABLE environmental conditions The different types of reproduction correlate w/ seasons Ex: in bees, haploid male drones are produced parthenogenetically from unfertilized eggs laid by reproductive females (queens) while new queens and sterile workers develop from fertilized eggs

The conditions set the switch for which form of reproduction occurs:

Polyspermy

The phenomenon in which more than one sperm fertilizes an egg, can be PREVENTED by two mechanisms: a fast block within seconds of fertilization and a slow block within minutes In inverts such as sea urchins, the fusion of egg and sperm opens ion channels in the plasma membrane of the egg, spreading a wave of electrical depolarization over the egg surface, much like the nerve impulse traveling along a neuron The depolarization alters the egg plasma membrane's potential from negative to positive so that it cannot fuse w/ addition sperm It occurs within a few secs after fertilization, the barrier set up by the wave of depolarization is called fast block polyspermy In verts, the wave of membrane depolarization following sperm-egg fusion is NOT AS PRONOUNCED, and does not prevent additional sperm from fusing w/ the egg However, any additional sperm nuclei entering the egg cytoplasm usually break down and disappear so that ONLY the FIRST sperm nucleus to enter fuses w/ the egg nucleus In both inverts and verts, fusion of egg and sperm triggers release of stored calcium (Ca2+) ions from the endoplasmic reticulum of the egg into the cytosol The Ca2+ ions activate control proteins and enzymes that initiate intense metabolic activity in the fertilized egg, including a rapid increase in cellular oxidations and synthesis of proteins and other molecules These ions also trigger the cortical reaction, in which CORTICAL GRANULES, secretory vesicles just under the plasma membrane of the egg, fuse w/ the membrane and release their contents to the outside by exocytosis Enzymes released from the cortical granules alter the egg coats w/in minutes after fertilization, so that NO FURTHER SPERM can attach and penetrate to the egg This barrier termed, slow block to polyspermy, is set up = NO MORE SPERM can reach the egg plasma membrane in any animal species After the sperm nucleus enters the egg cytoplasm, microtubules move the sperm and egg nuclei TOGETHER in the egg cytoplasm and they FUSE The chromosomes of the egg and sperm nuclei then assemble together and enter mitosis

gametogenesis and fertilization

What are cellular mechanisms for Sexual Reproduction?

Asexual reproduction produces offspring with genes from only one parent. In most animals that undergo asexual reproduction, the offspring are produced by mitosis = genetically identical to one another and to the parent! Such genetic homogeneity can be advantageous in stable and uniform environments. Another advantage is that the individuals do not need to use energy to produce gametes or to find and select a mate. Further, for individuals in sparse populations, or for sessile animals, asexual reproduction can be an advantage. DISADVANTAGE for asexuality: a genetically homogenous population may not adapt easily to new environments Sexual reproduction always generates genetic diversity among offspring. This provides a population the opportunity to adapt to changing environments, and perhaps to move to and colonize new environments. DISADVANTAGE for Sexuality: Expenditure of energy and raw materials to produce gametes and to find and select mates. It produces FEWER offspring per parent. Asexual reproduction of a female produces all-female progeny, each of which can produce offspring for the next generation. HOWEVER, in sexual reproduction, only ½ of the progeny of a mating are females, and only they can produce the offspring for the next generation.

What are the advantages and disadvantages of asexual reproduction? Of sexual reproduction?

spermatogonia and oogonia these cells enter meiosis to give rise to GAMETES by spermatogenesis and oogenesis in humans, each gamete has only one of 2^23 possible combinations of parental chromosomes

What do mitotic divisions of germ cells produce?

Internal Fertilization

taking place in a watery fluid inside the body of the female Takes place in inverts. Such as annelids, some arthropods, and some mollusks, and in verts. Such as reptiles, birds, mammals, some fish, and some salamanders The sperm is released by the close to or inside the entrance of the reproductive tract of the female. The sperm swim through the fluids in the reproductive tract until they reach and fertilize each egg In some species, molecules released by the egg attract the sperm to its outer coats The physical act involving the introduction of the male's accessory sex organ (penis) into a female's accessory sex organ (vagina) to accomplish internal fertilization is known as copulation Makes terrestrial life possible by providing the aquatic medium required for fertilization inside the female's body without the danger of gametes drying by exposure to the air Male reptiles, birds, and mammals have accessory sex organs that place sperm directly inside the reproductive tract of females, where fertilization takes place In reptiles and birds, sperm fertilize eggs as they are released from the ovary and travel through the oviducts, BEFORE the shell is added In mammals, the male's penis delivers sperm into the female's vagina Unlike the cloaca in reptiles and birds, which has BOTH sexual and excretory functions, the vagina is specialized for reproduction The introduced sperm swim into the tubular oviducts containing the eggs, and fertilization takes place

External Fertilization

taking place in a watery medium outside the bodies of both parents Occurs in most aquatic inverts., bony fish, and amphibians, sperm and eggs are shed into the surrounding water Sperm swim until they collide w/ an egg of the same species Process is helped by synchronization of female and male gametes released, and by the enormous quantities of gametes released, as exemplified by the palolo worms Sea urchins and amphibians: the sperm are attracted to the egg by diffusible attractant molecules released by the egg Most amphibians, even terrestrial species such a toads, mate in an aquatic environment. Frogs typically mate by a reflex response called AMPLEXUS, in which the male clasps the female tightly around the body w/ his forelimbs The embrace stimulates the female to shed a mass of eggs into the water through the CLOACA, the cavity in reptiles, birds, amphibians, and many fishes into which both the intestinal and genital tracts empty As eggs are released, they are fertilized by sperm released by the male

Gametogenesis

the formation of male and female gametes

Mating

the pairing of a male and a female for the purpose of sexual reproduction