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36 Cards in this Set
- Front
- Back
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Asexual Reproduction
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- Efficient bc no time/energy is wasted on mating and every member of the population can convert resources into offspring
- Does not generate genetic diversity |
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Characteristics of those who reproduce asexually
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- Mostly invertebrates
- Tend to be species that are attached to their substrate and cannot search for mate or live in sparse populations and rarely encounter potential mates - Found in constant environments where genetic diversity is less important for species success - Good way to preserve a genotype that is successful in a particular environment if the environment doesn't chnage |
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Budding
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- Model of Asexual Reproduction
- More or less complete new organism grows from the body of the parent organism, eventually detaching itself |
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Regeneration
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- Model of Asexual Reproduction
- Development of a complete individual from a fragment of an organism - Echinoderms (Starfish) - Can occur when an animal is broken by an outside force such as wave action in the intertidal zone - Some species of segmented marine worms develop segments with rudimentary heads bearing sensory organs - Segments then break apart, and each one forms a new worm |
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Parthenogenesis
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- Model of Asexual Reproduction
- Production of an organism from an unfertilized egg - Common in arthropods, some species of fish, amphibians, and reptiles - Most species that reproduce parthenogenetically also engage in sexual reproduction or at least sexual behavior at other times - In some species, parthenogenesis is part of the mechanism that determines sex - Honey bees: males develop from unfertilized eggs, haploid; females develop from fertilized eggs, diploid - Reproduction sometimes requires sexual behavior |
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3 Steps of Sexual Reproduction
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- Gametogenesis: making gametes
- Spawning (mating): bringing gametes together - Fertilization: fusing (union of) gametes |
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Gametogenesis
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- Specialized series of cellular divisions that leads to the production of gametes
- Requires the joining of 2 haploid cells (gametes) into one - production involves meiotic cell division --> diploid individual |
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Genetic Diversity
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- Two events in Meiosis
- Crossing over of homologous chromosomes - Independent assortment of the chromosomes |
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Gonads
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- Organ that produces gametes in animals.
- Testes or Ovaries |
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Sperm
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- Male gametes, move by beating their flagella
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Egga or Ova
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- Female gametes, nonmotile
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Germ Cells
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- Reproductive cell or gamete of a multicellular organism
- Early in the developing embryo - Forms gametes |
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Germ Cells
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- Cells are sequestered in the body of the embryo until its gonads begin to form
- Cells then migrate to the developing gonads, where they take up residence and proliferate by mitosis, producing spermatogonia in males and oogonia in the females. Both are diploid and multiply by mitosis - Next, meiotic cell division reduces the chromosomes to the haploid number. - Spermatogonia and oognia that enter meiosis are primary spermatocytes and primary oocytes |
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Primary Spermatocytes
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- Diploid progeny of a spermatogonium
- Undergoes the first meiotic division to form secondary spermatocytes |
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Primary Oocytes
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- Dipoid progeny of a oogonium
- In many species, a primary oocyte enters prophase of the first meiotic division, then remains in developmental arrest for a long time before resuming meiosis to form a secondary oocyte and a polar body |
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Types of Gametogenesis
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- Spermatogenesis
- Oogenesis |
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Spermatogenesis
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- Gametogenesis leading to the production of sperm. Initial proliferation of male germ cells into spermatogonia proceeds by mitosis in the embryo
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Process of Spermatogenesis
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- Primary spermatocytes undergo the first meiotic division to form secondary spermatocytes
- Second meiotic divison produces 4 haploid spermatids: [One of the products of the second meiotic division of a primary spermatocyte; four haploid spermatids, which remain connected by cytoplasmic bridges, are produced for each primary spermatocyte that enters meiosis.] for each primary spermatocyte that enters meiosis - In mammals, the progeny of primary spermatocytes remain connected by cytoplasmic bridges after each division. Remain in cytoplasmic contact throughout their development partly o Half secondary spermatocytes receive an X chromosome, other half a Y chromosome. o Y chromosome contains fewer genes than the X chromosome, and some of the products of genes found only on the X chromosome are essential for spermatocyte development. By remaining in cytoplasmic contact, all four spermatocytes can share the gene products of the X chromosomes, although only half of them have an X chromosome. |
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Oogenesis
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- Gametogenesis leading to the production of an ovum
- Female germ cells divide by mitosis to form oogonia and then oocytes |
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Process of Oogenesis
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- A primary oocyte immediately begins prophase I of meiosis
- After prophase I development stops in many species • In human female, this period is at least 10 years, until puberty, and some primary oocytes remain in prophase I for 50 years, until menopause. - Primary oocyte grows larger through the increased production of ribosomes, RNA, cytoplasmic organelles, and energy stores; and acquires nutrients - When meiosis resumes, the nucleus of the oocyte completes the first meiotic divison near the surface of the cell: divides into 2 daughter cells of unequal sizes (unequal shares of cytoplasm) • Secondary oocyte: cell with more cytoplasm • First Polar Body: smaller one - The second meiotic division of the large secondary oocyte is also accompanied by asymmetrical division of the cytoplasm. • One daughter cell forms the large, haploid ootid, which eventually differentiates into a mature ovum, the other forms the second polar body. • Polar bodies degenerate, so the end result of oogenesis is only one mature egg for each primary oocyte that entered meiosis. Egg is large, well-provisioned cell - A second period of arrested development occurs after the first meiotic division forms the secondary oocyte - The egg may be expelled from the ovary in this condition • In many species, including humans, the second meiotic division is not completed until the egg is fertilized by the sperm |
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Differences between Spermatogenesis and Oogenesis
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- After prophase I development stops in many species
o In human female, this period is at least 10 years, until puberty, and some primary oocytes remain in prophase I for 50 years, until menopause. o Unlike spermatogenesis, which continues uninterrupted to completion once the primary spermatocyte has differentiated. - When meiosis resumes, the nucleus of the oocyte completes the first meiotic divison near the surface of the cell: divides into 2 daughter cells of unequal sizes (unequal shares of cytoplasm) o Represents another major difference from spermatogensis, in which cytoplasm is apportioned equally |
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Fertilization
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- Fusion of gametes (haploid sperm and haploid egg), known as syngamy
- Creates a single diploid cell, zygote, develops into an embryo |
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External Fertilization
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- Requires an aquatic habitat in which the gametes are released for transport
o Timing and amount of release are important, as well as synchronization of male and female reproductive activities o Day length, temperature changes, weather changes, and social stimulation are important regulators of external fertilization o Behavior may play a vital role in bring gametes together |
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Internal Fertilization
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- Release of sperm into the female reproductive tract; typical of most terrestrial animals; important evolutionary step in the colonization of land by animals
o For animals practicing this type of fertilization, mating behaviors help guarantee species specificity, but egg-sperm recognition mechanisms still exist. o Cumulus, Zona Pellucida, Accessory Sex Organs |
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Cumulus
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- Consists of a loose assemblage of maternal cells in a gelatinous matrix. Surrounds the mammalian egg
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Zona Pellucida
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Jellylike substances, glycoprotein envelope that surrounds the mammalian ovum when it is released from the ovary
- Found beneath the cumulus - Functionally similar to the vitelline envelope of sea urchin eggs |
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Accessory Sex Organs
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- Enables fertilization
- Development of penis: tube for depositing sperm in the female reproductive tract - Copulation: physical joining of the male and female accessory organs |
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Process of Fertilization
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• Sperm and egg recognize each other
• Sperm is activated so that it can gain access to the plasma membrane of the egg • Plasma membranes of a single sperm and egg fuse • Egg blocks entry of additional sperm • Egg is metabolically activated stimulated to start development • Egg and sperm nuclei fuse = zygote |
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Specificity in Sperm-Egg Interactions
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Specific recognition molecules mediate interactions b/w sperm and eggs. These molecules ensure that the activities of the sperm are directed toward
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Blocks to Polyspermy
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- The fusion of the sperm and egg plasma membranes and the entry of the sperm into the egg initiate a programmed sequence of events. The first responses to sperm entry are blocks to polyspermy—that is, mechanisms that prevent more than one sperm from entering the egg. If more than one sperm enters the egg, the embryo is unlikely to survive.
- hCG |
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Human Chorionic Gonadotropin (hCG)
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- Hormone secreted by the placenta which sustains the corpus luteum and helps maintain pregnancy
• Secreted by the blastocyst after implantation in the uterus • Keeps the corpus luteum functional (stimulates it to continue to produce estrogen and progesterone to support growth and maintenance of the endometrium and thereby prevent menstruation) • Presence of this hormone is the basis for pregnancy testing • Tissues derived from the blastocyst also begin to produce estrogen and progesterone. |
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How Human Male and Female Reproductive Systems Work
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REPRODUCTIVE ORGANS >> HORMONES >> PURPOSE
- Anterior Pituitary >> FSH/LH >> Growth of follicles/Ovulation - Ovaries >> Estrogen/Progesteron >> Growth of mother sex organs: cuases LH (responsible for ovulation) surge/Prepare and maintain uterus - Testes >> Testosterone >> Sex Characteristics - Placenta >> hCG >> Stimulates corpus luteum to grow and release estrogen and progesterone |
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Female Reproductive Cycle
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- Ovarian Cycle
- Uterine Cycle o The Ovarian and Uterine cycle are coordinated and timed by the same hormones that initiate sexual maturation. o Gonadotropins (FSH and LH) secreted by the anterior pituitary are the central elements of this control o Before puberty, the secretion of FSH and LH is low and the ovaries are inactive. o At puberty, the hypothalamus increases its release of GnRH, stimulating the anterior pituitary to secrete FSH and LH. o In response to FSH and LH, the ovarian tissue grows and produces estrogen. The rise in estrogen causes the maturation of the accessory sex organs and the development of female secondary sexual characteristics. B/w puberty and menopause, interactions of GnRH, gonadotropins, and sex steroids control the ovarian and uterine cycles o Menstruation marks the beginning of each of these cycles o A few days before menstruation begins, the anterior pituitary begins to increase its secretion of FSH and LH. o In response, some 10-20 follicles begin to mature in the ovaries, and these follicles steadily increase their production of estrogen. o After about a week, all but one of the follicles wither away o Estrogen exerts negative feedback control on gonadotropin release by the anterior pituitary during the first 12 days of the ovarian cycle. o Day 12, estrogen exerts postive rather than negative feedback control on the pituitary. o As a result, a surge of LH and a lesser surge of FSH occur o LH surge triggers the mature follicle to rupture and release its egg, and it stimulates the cells of the ruptured follicle to develop into a corpus luteum o Corpus luteum becomes an endocrine gland o Estrogen and especially progesterone secreted by the corpus luteum following ovulation are crucial to continued growth and maintenance of the endotrium o Additionally, these sex steroids exert negative feedback control on the pituitary, inhibiting gonadotropin release and thus preventing new follicles from beginning to mature o If the egg is not fertilized, the corpus luteum degenerates on about day 26 of the cycle. o Without production of progesterone by the corpus luteum, the endometrium sloughs off and menstruation occurs o Decrease in circulating steroids also releases the hypothalamus and pituitary from negative feedback control, so GnRH, FSH, and LH all begin to increase. o Increase in these hormones induces the next round of follicle development, and the ovarian cycle begins again. |
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Ovarian cycle
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- Produces eggs and hormones
- Repeats about every 28 days (monthly) - Woman's fertile years total about 450 ovarian cycles - In each cycle, one oocyte matures and is released • During first half of each cycle, at least one primary oocyte matures into a secondary oocyte (egg) and is expelled from the ovary (ovulation) • During the second half of the cycle, cells in the ovary that were associated with the maturing oocyte develop endocrine functions and then regress if the egg is not fertilized. • Menopause: end of fertility. Occurs at about age 50, and only a few oocytes are left in each ovary • During fertile years, a woman goes through about 450 ovarian cycles • During each cycle, several oocytes begin to mature, but usually only one matures completely and is released; the others degenerate • Each primary oocyte in the ovary is surrounded by a layer of ovarian cells |
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Uterine Cycle
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- Prepares the endometrium for the arrival of a blastocyst=embryo
• Parallels the ovarian cycle • Consists of a buildup and then a breakdown of the endometrium (epithelial lining of the uterus) • About 5 days into the ovarian cycle, the endometrium starts to grown in preparation for receiving a blastocyst. • Uterus attains its maximal state of preparedness about 5 days after ovulation and remains in that state for another 9 days • If a blastocyst has not arrived by that time, the endometrium begins to break down, and the soughed-off tissue, including blood, flows from the body through the vagina = menstruation |
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Sexually Transmitted Diseases
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• Disease parasites have evolved using sexual contact b/w their hosts as their means of transmission.
• Include viruses, bacteria, yeasts, and protozoans • Chlamydia and gonorrhea are not fatal but make cause infertility and painful diseases • Syphilis – a spirochete – fatal in about 50% of untreated cases • AIDS: transmitted by a virus, is of recent origin and has a high rate of mortality • Condom – only birth control device that is effective against STDs |
