animal reproduction chapter 46
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ANIMAL REPRODUCTION Chapter 46. Asexual- mitotic Sexual- both mitotic and meiotic divisions Increases genetic variability due to combination of genes from two parents Have variety of phenotypes. Asexual reproduction: - invertebrates- fission, budding (colonies) - PowerPoint PPT PresentationTRANSCRIPT
ANIMAL REPRODUCTIONChapter 46
Asexual- mitotic
Sexual- both mitotic and meiotic divisions
-Increases genetic variability due to combination of genes from two parents
-Have variety of phenotypes
Asexual reproduction:
- invertebrates- fission, budding (colonies)
- sea stars, sponges, annelids- fragmentation and regeneration
Advantages:
-enables isolated animals to reproduce
- enables creating lots of offspring in short time
- in favorable environments perpetuates successful genotypes precisely
Reproductive cycle: - periodic nature allows animals to conserve resources
and reproduce when environment is favorable and more energy is available.
- controlled by hormones and environmentPARTHENOGENESIS: - fresh water crustacean- Daphnia- produce eggs of
two types. Haploid adults produce eggs without meiosis
- bees, wasps, ants- males (drones) are produced parthenogenetically
- among vertebrates, several genera of fishes, amphibians and lizards reproduce by a complex parthenogenesis- doubling of chromosomes after meiosis. Ex. whiptail lizards - no males, one female mimics a male.
Hermaphroditism: earth worm
- produce double the number of offspring
Sequential hermaphroditism: individual reserves its sex during its life time
Ex: Caribbean blue head wrasse (reef fishes)- female- first species- largest female becomes male
Oysters- male- first species
Fertilization: - depends on mechanisms that help sperm meet eggs
of the same species. - external- requires moist habitat- prevents gametes
from drying, allow sperm to swim to eggs. Timing is crucial to ensure mature sperm encounter ripe egg.
- temperature or day length cause a whole population to release gametes at once.
- Chemical signals from one individual releasing gametes trigger gamete release in others.
- individuals may exhibit specific mating behaviors leading to fertilization of eggs one female by one male – courtship – which allows mate selection and increases probability of successful fertilization – by triggering release of both sperm and eggs.
Internal- adaptation to terrestrial life
- enables sperm to reach an egg when environment is dry
- requires cooperative behavior which leads to copulation
- requires sophisticated reproductive systems including copulatory organs and receptacles.
Pheromones:
- chemical signals released by one organism that influence the physiology and/ or behavior of other individuals of the same species.
- they are small volatile or water soluble molecules active in small amounts
- function as mate attractants
Ensuring the survival of offspring:
- produce more offspring than can survive to reproduce
- internal fertilization produce fewer zygotes – greater protection of the embryos and parental care of the young.
- protection- tough egg shells, development of embryo within the reproductive tract of the mother, parental care of the eggs and offspring
- embryo develop within the egg
- embryo remain within reproductive tract of the female
- marsupials
- eutherians (placental) - embryos develop entirely within the uterus
Gamete production and delivery:
- Gonads are organs that produce gametes in most organisms
- polychaete worms (annelids) has simplest system, have separate sexes but no distinct gonads- gametes develop from undifferentiated cells lining the coelom
- mature gametes are released from the wall into the coelome
- mature gametes shed through excretory openings or swelling mass of eggs may split the body open, killing the parent
complex reproductive system include - sets of accessory tubes and glands that carry,
nourish, and protect the gametes and developing embryos
- Parasitic flatworms- hermaphrodites- most complex in animal kingdom
- most insects have separate sexes with complex reproductive systems
- in male- sperm develop in a pair of testes and are conveyed along a coiled duct to two seminal vesicles where they are stored.
- During mating sperm are ejaculated into female system
- In female eggs develop in pair of ovaries, conveyed through ducts into vagina, fertilization occurs
- in many species female system includes spermatheca, a sac in which sperm may be stored for a year or more.
- in many nonmammalian vertebrates, digestive, excretory and reproductive systems have a common opening – cloaca
CONCEPT 46.3 - for SDL
Concept 46.4 In humans and other mammals, a complex
interplay of hormones regulates gametogenesis - Spermatogenesis- a continuous prolific
process - each ejaculation of human male contains 100
to 650 million sperm cells - spermatogenesis occurs in the seminiferous
tubules of the testes. - primordial germ cells of embryonic testes
differentiate into spermatogonia(2n) – spermatocytes (n) – spermatids (n) – sperm cells (P. No. 975)
Oogenesis differs from spermatogenesis in three major ways.
- during meiotic division of oogenesis, cytokinesis is unequal- only one cell- secondary oocyte develop into egg; in spermatogenesis all four cells of meiosis develop into sperms
- cells from which sperms develop, continue to divide by mitosis throughout males life, which is not the case in human female
- Oogenesis has long resting periods, sperms are produced from precursor cells in an uninterrupted sequence
The Reproductive Cycles of Females:
- secretion of hormones and reproductive events are cyclic in female
- males produce sperms continuously
Menstrual versus Estrous Cycles:
- menstrual (uterine cycle) - in humans and certain other primates
- ovulation occurs after endometrium thicken and develop a rich blood supply
- in menstrual- endometrium is shed- menstruation
Estrous cycle:
- endometrium is reabsorbed by uterus and no extensive bleeding
- more pronounced behavioral changes
- stronger effect of season and climate
- most mammals copulate only during period surrounding ovulation- this period of sexual activity- estrus- is the only time the condition of vagina permits mating
- estrus= heat
Duration of menstrous cycle
- human 28 days; estrous- rat 5 days; bears and dogs one cycle per year; elephants several
The Human Female Reproductive Cycle:
- it’s an integrated cycle involving two organs, uterus and ovaries- controlled by hormones.
- gonadotropin- releasing hormone (GnRH)- hypothalamus; FSH and LH- anterior pituitory
- concentration of FSH and LH in blood control production of 2 steroid hormones– estrogen and progesterone
- ovarian cycle of hormones control uterine cycle of endometrial growth and loss.
The Ovarian Cycle: - cycle begins with release of GnRH - stimulates pituitory to release small amount of FSH
and LH - they stimulate follicle growth - cells of growing follicles start to make estrogen - several follicle grow, but only one matures others
disintegrate - high level of estrogen stimulates secretion of FSH and
LH particularly LH- positive feedback - LH induces final maturation of follicles - maturing follicle develops an internal fluid- filled cavity
and grows big - follicle and adjacent wall of the ovary rupture
releasing secondary oocyte
- following ovulation, during luteal phase, LH stimulates the transformation of follicular tissue to form corpus luteum, a glandular structure
- corpus luteum secretes progesterone and estrogen
- as these concentration increases, produce negative feed back on hypothalamus and pituitary, inhibiting secretion of FSH and LH.
- near the end of luteal phase, corpus luteum disintegrates, causing decline in estrogen and progesterone level releasing their inhibitory action on hypothalamus and pituitary- stimulates growth of new follicles, initiating next ovarian cycle.
The Uterine( menstrual ) cycle: - hormones secreted by the ovaries estrogen and
progestrone have major effect on uterus. - high amount of estrogen secreted by follicles signals
endometrium to thicken. - follicular phase of ovarian cycle is coordinated with
proliferative phase of uterine cycle. - after ovulation estrogen and progesteron secreted by
corpus luteum stimulate continued development and maintenance of endometrium, arteries and endometrial glands.
- glands secrete a nutrient fluid that sustain an early embryo.
- luteal phase of ovarian cycle is coordinated with secretory phase of uterine cycle.
- rapid drop of ovarian hormones when corpus luteum disintegrates results in menstruation- the menstrual flow phase of uterine cycle and beginning of new cycle.
- estrogen induces deposition of fat in the breasts and hips, increases water retention, affects calcium metabolism, stimulates breast development and influences female sexual behavior.
Menopause: after about 450 cycles, between ages of 46 to 56. ovaries lose their responsiveness to gonadotropins, decline in estrogen production in ovaries
Hormonal Control of the Male Reproductive System:
- principle sex hormones are androgens- testosterone, steroid hormones produced by the Leydig cells of testes, interstitial cells located near the seminiferous tubules.
- primary and secondary characteristics of the male.
- primary sex characters are associated with reproductive system, development of vasa differentia and other ducts, external reproductive structures and sperm production
- androgens determine behavior in mammals
- hormones from anterior pituitary and hypothalamus control androgen secretion and sperm production
Pregnancy or gestation
- correlates with body size
- human-266 days; rodents- 21 days; dogs- 60 days; cows- 270 days; elephants- more than 600 days
Conception, Embryonic development, and Birth:
-fertilization in oviduct, after 24hrs zygote begins cleavage, after 3-4 days zygote reaches uterus as a ball of cells, after a week- blastocyst - a sphere of cells containing a cavity which implants into the endometrium.
- embryo secretes hormones that signal its presence and control mothers reproductive system – human chorionic gonadotropin (HCG)- act like pituitary LH to maintain secretion of progesterone and estrogen by corpus luteum – through first few months of pregnancy
- absence of this decline maternal LH due to inhibitory action of pituitary, results in menstruation and loss of embryo.
First Trimester: - human gestation – 3 trimesters about 3 months
each - First trimester: most radical change both in
mother and embryo - endometrium responds to implantation by
growing over the blastocyst - differentiation of embryo’s body structures now
begins - first 2-4 weeks of development, embryo
obtains nutrients from the endometrium, outer layer of blastocyst- trophoblast, grows out and mingles with endometrium, helping to form placenta; umbilical cord
- first trimester is the main period of organogenesis
- heart begins beating by the 4th week
- by the end of 8th week, all major structures of the adult are present in rudimentary form. Now embryo is called fetus.
- high level of progesterone in mother initiate changes in her reproductive system; increased mucus in the cervix that forms a protective plug, growth of maternal part of placenta, enlargement of uterus, cessation of ovulation and menstrual cycling, breasts enlarge and are tender.
Second Trimester:
- fetus grows about 30cm and is very active
- mother feel the movement
- placenta takes over the production of progesterone
Third Trimester:
-fetus grows to 3-4 kg in weight and 50 cm length
- fetus fills the available space within the embryonic membrane
- mothers abdominal organs compress; a complex of local regulators (prostaglandins) and estrogen and Oxytocin induces and regulates labor
- parturition; lactation (postnatal care)
Parturition is brought about by a series of strong rhythmic uterine contractions.
Process of labor has three stages.
First- opening up and thinning of cervix
Second- expulsion or delivery of baby
Third- delivery of placenta.
Lactation: prolactin stimulates milk production
oxytocin release milk from mammary gland.
Contraception – deliberate prevention of pregnancy.
Prevent release of mature egg and sperms from the gonads, prevent fertilization, prevent implantation.
Modern reproductive Technology – genetic and other congenital disorders.
Amniocentesis and chorionic villus sampling – invasive techniques.
Ultrasound imaging – noninvasive technique.
Solutions for infertility: Assisted Reproductive Technology (ART)
In vitro fertilization (IVF)
Zygote Intrafallopian Transfer (ZIFT)
Gamete Intrafallopian Transfer (GIFT)