Animal Reproduction and Development (bio 2 final)

asexual reproduction

-offspring are produced from a single parent and are clones of the parent

-same genes-no genetic variation

types of asexual reproduction

-budding

-regeneration/fragmentation

-fission

budding

-portion of parent pinches off to form a completely new individual

-ex: hydra, many cells forming a bud

regeneration/fragmentation

-complete organism formed from a fragment of parent’s body

-ex: flatworms

fission

-parent divides mitotically into two nearly equal parts

-ex: protozoans, simple cell division

sexual reproduction

-requires MEIOSIS followed by CYTOKINESIS REDUCTION DIVISION

-2 haploid gametes fuse to produce new individual

-offspring is genetically different from parents- genetic variation

-most species sexually reproduce

-energetically expensive (esp. on female side)

-1N+1N=2N

-development of zygote forms embryo

advantages of asexual reproduction

-one parent; no gametes; no reproductive organs

-simple way to produce many copies of an individual

-result of mitosis/cytokinesis (mostly)

-can reproduce if isolated and at any time

-energetically cheap

disadvantages of asexual reproduction

-genetically the same

-more prevalent in species with a stable environment and lots of resources

-LITTLE SELECTION PRESSURE for genetic diversity (no survival of the fittest)

advantages of sexual reproduction

-greater genetic variation

-may allow rapid adaptation to environment changes

disadvantages of sexual reproduction

-2 types of gametes must be made

-male and female requires specialized body parts and must find a mate

types of sexual reproduction

-hermaphroditism

-parthenogenesis

-biparental reproduction

hermaphroditism

-individuals have both male and female reproductive organs-each individually capable of producing offspring

-MONOECIUS

monoecius

-condition where both types of sex organs in same individual

-most examples exhibit cross fertilization(2 individuals); self fertilization uncommon

-sex reversal on occasion (fish)

parthenogenesis

-development of an embryo from an unfertilized egg

-sperm may or may not be involved with initiation of development

-sperm does not fuse with egg but it does trigger certain hormonal developments to help drop the egg

-AMEIOTIC

-MEIOTIC

-has been described in all vertebrate animals except mammals

ameiotic

-no meiosis and egg forms by mitosis/cytokinesis

meiotic

-egg forms by meiosis (haploid) and develops without fusing with sperm

biparental reproduction

-2 genetically different individuals

-2 types of sex organs producing 2 types of gametes (sex cells)

-DIOECIOUS

-FUSION OF EGG AND SPERM

dioecious

-condition of separate sexed individuals

reproductive modes in vertebrates

-oviparous

-ovoviviparous

-viviparous

oviparous

-condition of egg laying outside of body

-fertilization may be external or internals

-eggs may be abandoned

-fish, amphibians, reptiles, birds, mammals(3 species)

-simple but not primitive

ovoviviparous

-condition of eggs (within some form of shell like structure) retained in female’s body

-fertilization MUST be internal

-all nourishment derived from yolk of egg

-NO maternal connection

-offspring are born live but enclosed

-enclosed in sac but emerges quickly after birthing

-fish, amphibians, reptiles

viviparous

-condition of live bearing with a maternal connection

-PLACENTA-connecting structure with uterus

-requires internal fertilization

-nourishment and gas exchange with placenta

-live bearing is highest degree of parental care

-fish, reptiles, mammals

gametogenesis and fertilization

-gametes (sex cells) are formed in gonads

-testes in males, ovaries in females

-gametogenesis—>spermatogonia or oogonia

-primordial germ cells arise from yolk sac and migrate to primitive gonad

-vertebrate gonads arise from pair of genital ridges along the dorsal body wall and migrate to lower trunk region

-some spermatogonia and oogonia multiply again by mitosis to produce primary spermatocytes and primary oocytes

-these undergo meiosis to form haploid gametes (sperm and egg) eventually

-spermatogenesis

-oocytes

-mammalian oogenesis

-fertilization

gametogenesis

-begins with germ cells that multiply by mitosis to produce spermatogonia (diploid) or oogonia(diploid)

spermatogenesis

-primary spermatocytes undergo mitosis I to produce 2 haploid secondary spermatocytes

-eventually develops into sperm

-one diploid cell becomes 4 gametes (haploid)

-spermatogonium 2N—> primary spermatocytes 2N—> secondary spermatocytes 1N—> spermatids 1N—> mature sperm cells 1N

oocytes

-1 gamete produced from each primary oocyte

-meiosis I produces 1 large secondary oocyte plus a smaller polar body which eventually degenerates

-1 or many ova can develop at a time

-oocytes develop within follicles in the ovaries and are released during ovulation (rupturing of follicle)

-timing is longer on female side and there’s dormancy at a certain period

mammalian oogenesis

-begins in the fetus before birth

-cohort of germ cells enter meiosis I and arrest- well not resume development until puberty

-Meiosis I is completed in some primary oocytes to produce haploid secondary oocytes

-meiosis II

-fusion of the 1N egg nucleus with a haploid sperm nucleus produces a 2N zygote

-oogonium 2N—> primary oocyte 2N—>secondary oocyte 1N—> secondary polar body 1N degenerates and haploid egg 1N(diploid zygote once the egg and sperm nuclei fuse)

fertilization

-haploid egg and sperm unite to form a 2N zygote

-sperm swims toward egg

-sperm uses proteolytic enzymes in acrosome (protective cap) to digest the plasma membrane of egg

mammalian reproductive structure and function

-male genitalia

-testes composed of seminiferous tubules

-sperm

-hormonal control of male reproductive system

-testosterone

-ovary

-female reproductive tract

-oocytes

-fertilization

-hormonal control of female reproductive system

male genetalia

-consists of penis and scrotum

-scrotum holds testes where sperm develops at 2 degrees celsius lower than core body temp

testes

-composed of seminiferous tubules and leydig cells

seminiferous tubules

-site of spermatogenesis

-begins at puberty and continues throughout life

leydig cells

-endocrine cells that secrete testosterone

-SERTOLI cells provide nutrients and protection to developing sperm

sperm

-sperm are released into LUMEN of seminiferous tubules

-move into EPIDIDYMIS to complete their differentiation by becoming motile and capable of fertilization

-then to VAS DEFERENS leading to EJACULATORY DUCT and urethra

-semen contains fluid and sperm

-sperm is 50% of the volume of semen ( fluid from seminal vesicles (fructose), bulbourethral glands (fluid), and prostate gland (fluid))

hormonal control of male reproductive system

-hypothalamus secretes LH-RH and FSH-RH—> bloodstream—> gonads

-FSH initiates sperm production in seminiferous tubules

-LH stimulates leydig cells to secrete testosterone

testosterone

-stimulates growth of male reproductive tract and genitalia during development and puberty

-stimulates development of male sexual characteristics-facial hair, horns on bulls, bright feathers on peacocks

ovary

-production of ovum (egg)

-hormone secretion- estrogen and progesterone

-primordial cells producing oogonia form during embryonic development

-much more time and energy required than male

female reproductive tract

-female genitalia differentiate from the same embryonic tissue as male genitalia

-Labia Majora

-Labia Minora

-Clitoris

-urethra is not part of the reproductive tract in females

-openings of reproductive tract and urethra are separate

-external opening of reproductive tract leads to vagina, cervix, and into uterus

-uterus has inner glandular lining (endometrium) that builds up for implantation

labia majora

-same tissue as scrotum

labia minora

-same tissue as urethral primordial tissue

clitoris

same erectile tissue as penis

oocytes

-develop in 1 of 2 ovaries

-typically 1 secondary oocyte released and is quickly drawn into oviduct (fallopian tube)

-moves down oviduct by cilia

-fertilization usually in oviduct (upper 40%)

-zygote develops into blastocyst ( a ball of 32-150 cells) and enters the uterus

fertilization

-uterus is the implantation site

-many cell divisions to become blastocysts

-endometrium builds up with vessels and epithelial tissue

-if fertilization happens and implantation occurs- endometrium continues to develop and is maintained by hormonal activity

-connection is the PLACENTA

-if fertilization/implantation does not occur, endometrium sloughs off and is is discharged

hormonal control of female reproductive system

-hypothalamus secretes LH-RH and FSH-RH —> bloodstream—> pituitary gland—> bloodstream—> gonads

-FSH-stimulates development of ovarian follicles and estrogen and progesterone by follicles

-LHH- stimulates secretion of progesterone and estrogen by corpus luteum (remnant of follicle after ovulation)