Reproduction Flashcards
what are the two types of reproduction
sexual and asexual
characteristics of asexual
-genetically identical offspring
-no genetic diversity
sexual reproduction
-diploid individual (2n) produces haploid sex cells (n) called gametogenesis
-haploid sex cells (n) unite to from new diploid individual (fertilization)
-mixing of genetical material provides genetic diversity
budding
-a new individual arises from an outgrowth of and older one
-common in sponges and some cnidarians
fission
-one individual separates into 2 or more individuals about equal size
-bacteria, some cnidaria
fragmentation/regeneration
-individual breaks into small pieces
-each individual can form a new piece
-come cells must dedifferentiate
-some echinoderms
parthenogenesis
-development of an individual form an unfertilized egg
-common in arthropods, some fish, amphibians, and lizards
-can be used for sex determinatioin
-e.g. ants, bees
-females diploids (fert)
-males haploids (pathogenesis)
why do some creatures go between asexual and sexual reproduction
-depending on environmental conditions
-when conditions are unfavourable they reproduce sexually
-when conditions are favourable they reproduce asexually
-the genetic conditions increase genetic diversity so increase survival
spontaneous hermaphroditism
-have both ovaries and testes
-but dont self fertilize to increase genetic diversity
-earth worm
sequential hermaproditism
-change sex
-protogynous - female before male (sea bass)
-protoandrous - male before female (clownfish)
why does genetic variability increase for sexual reproduction
-independent assortment of homologous chromosomes during meiosis I
-1 homogoue form each parent
-more chromosomes=more combinations
-e.g human haploid # (n)=23 so 2^n=2^23 = ~8.3 million combinations
-crossing over during prophase I- mixing of genes
-random fertilization
-8.3 million combinations of egg and sperm
-8.3 million x8.3 million =~70 trillion combos
gametogenesis
-haploid gametes produces by germ cells in primary sex organs
oogenesis
-females ovaries produce eggs (ova)
-large and non mobile
spermatogenesis
-testes produce sperm
-small and mobile
how spermatogenesis works
-each diploid parent cell produces 4 sperm cells
-each day ~3 million primary spermatocytes develop from diploid cells
-take 10 week (in humans)
how does the endocrine control spermatogenesis
-hypothalamus releases GnRH
-stimulates anterior pituitary
-which releases LH and FSH
-LH stimulates leydig cells which acts with FSH to produce sertoli cells
-producing testosterone
-causing spermatogenesis
and secondary sex characteristics
what do sertoli cells do
provide nutrition and support to maturing cells
HPG pathway/axis
hypothalmus, pituitary, gonad
oogenesis charicteristics
-one ovum produced in an ovarian cycle
-full complement of primary oocytes present at birth and held dorment (in prophase I) until puberty
the process of oogenesis
-1 primary oocyte not yet released from meiosis I. a cell layer is forming around it. the oocyte plus cell layer is a follicle
-2 the zona pellucida starts froming around the primary oocyte
-3 fluid filled cavity (antrum) starts forming in the follicles cell layer
-4 mature follicle. meiosis I is complete. the secondary oocyte and first polar body are now formed
-5 ovulation. the mature follicle ruptures releasing the secondary oocyte and first polar body
-corpus luteum forms form remnants of the ruptured folicle
-corpus luteum breaks down if the woman doesnt become pregnant
what happens to the primary oocyte
-female germ cell diploid
-forms primary oocyte (dip)
-forms haploid secondary oocyte (large) and first polar body (small)
-later a secondary polar body forms (small)
-later the polar bodies disintegrate
endocrine control of oogenesis and ovulation
-FSH stimulates one follicle to develop (complete meiosis I)
-estrodiol stimulates the growth and development of oocyte
-LH triggers ovulation
-progesterone prepares the uterus for receiving the embryo
mating
an anatomical and behavioural adaptations to bring gametes into close proximity for fertilization
anatomical adaptation of mating
secondary sex organs
behavioural adaptations of mating
mating rituals
fertilization
-combining two haploid gametes for form diploid zygotes
-internal and external fertalizatioin
sex hormones
-produced and secreted by gonads (ovaries and testies)
-estrogens
-progestins
-androgens
estrogen
maintain female reproductive system, development of female features
progestins
prepare uterus to support embryo
androgens
stimulates embryo to become male, maintain male reproductive system
how are sex hormones regulated
-by hypothalamus and anterior pituitary
-hypothalamus
-anterior pituitary
-follicle stimulating hormone
-luteinizing hormone
-gonads
-sex hormones
external fert occurs mainly in aquatic animals why?
maintaining osmotic balance is a challenge
what are the potential risks of external fertilization
-what is the water quality changes? temp, hypoxic etc
-other animals could eat eggs
how do animals compensate with the risks of external fertalizatioin
-produce a large number of eggs
what is the structure of the ovum
-egg nuclei
-cytoplasm
-2 polar bodies one on either side of the plasma membrane
-plasma membrane
-zona pellucida
-glycoprotein outer layer
what is the structure of sperm
-head: nucleus, acrosome
-midpiece: mitochondria
-tail: microtubules
cellular mechanism of fertilization (long)
-sperm contacts jelly layer of egg
-acrosomal reaction begins: enzyme contained in the acorosome are released and dissolve a path through the jelly layer
-proteins in its plasma membrane bind the sperm to the vitelline coat
-sperm lyses a hole in vitelline coat. the sperm and egg plasma membrane fuses
-membrane depolarization produces the fast block to polyspermy
-the sperm nucleus and centriole enter the egg. the sperm nucleus the fuses with egg nucleus
what does the fusion of egg and sperm trigger
the release of Ca2+ ions which trigger the cortical reaction, the fusion of secretary cortical granules with the eggs plasma membrane. the enzymes of the granules released to the outside alter the eggs coats producing the slow block to polyspermy
cellular mechanism of fertilization (summary)
-acrosome releases hydrolytic enzyme, dissolves the jelly coat
-sperm head binds to the receptor on the zona pellucia/vitelline layer
-fusion of sperm and ovum plasma membranes, sperm nucleus enters ovum
-activation of IP3CA2+ signalling pathway, separation and hardening of zona pellucida (fertilization membrane)
-fusion of two haploid nucleuses to from a diploid nucleus
what prevents fertilization of an ovum of different species
-especially for external fert
-the binding of the protein head to the receptor on the vitalline membrane is species specific tje receptors on the vitiline layer would not be able to bind to the sperm of another species
what prevents polyspermy
-fast block: all of the other receptors on the vitaline layer deacivates and cone no longer bind to another sperm
-slow blocks: the formation of ther fertalization membrane. this prevents others from approaching the cell
pros and cons for internal in external fert
ex-less energy
int-more protection
oviparous
-lay eggs, no support form parents
-evolution of amniotic egg
-e.g. birds
viviparous
-live young, nutrients, gases, etc. form parents
-e.g. most mammals (except monotreems)
ovoviviparous
-young develop in an egg inside parent often with live birth but little maternal support
-e.g some insects, sharks, snakes
what are the advantages and disadvantages to oviparity
-less requirement from mother
-eggs can be eaten
in oviparity how does the embryo receive nutrition and oxygen
-their eggs contain yoke which is very rich in nutrients
-calcarvious cells are porus for gass exchange
what happens after fertilization
-fertilization (forms zygote)
-cleavage: morula (solid ball of cells), blastula (hollowed ball of blastomeres-embryo)
-gastrulation: gastrula with primary tissue layers
-neurulation (formation of neural tube)
-organogenesis (major tissue and organ system)
characteristics of cleavage producing multi celled zygote
-mitotic cell division
-no new cytoplasm
-no increase in size or mass
-zygote partitioned into successively smaller cells
morula animal pole
-most active (small cells divide rapidly)
-in some species forms the embryo
morula vegetal pole
-less active (large cells divide slowly)
-may form yoke
morula blastocel
forms body cavity (coelom)
what does the blastula reflect
patterns of cleavage
key features of cleavage and blastula
-the series of mitotic division divides the zygote into many smaller cells (blastomeres)
-embryo doesnt increase in volume, and blastomeres become smaller and smaller with each division
-the ratio of nuclear volume to cytoplasmic volume in the embryo increases steadily during cleavage
-very little gene transcription occurs during cleavage
-blastomeres have certain developmental fates
why is there very little gene transcription during cleavage
because cell division occurs very rapidly
meteroblastic vs holoblastic
mero: incomplete cleavage (frogs)
holo:complete (mammals)
gastrulation charicteristics
-continued division and migration of embryonic cells
-form three germ layers (ecto, meso, endo)
-and primodial germ cells-gametes
-invagination at blastopore forms archenteron (early lined gut w misoderm)
gastrulation process
-surface blastomeres (bottle cells) migrate inside (invagination) that creates a small opening (blastopore)
-after invag cells at animal pole spread out over the surface of the embryo (ectoderm)
-cells at animal pole are pushed backwards towards the roof of blastocoel, creates a folding inside the embryo (archenteron)
-cells migrating into the interior of the of embryo differentiates into miso, ecto, and PGC
what organs and tissue does the ectoderm create
skin, nervous tissue, lens, retina, cornea of eye, lining of mouth, anus, sweat glands, mammary glands, adrenal medulla, tooth enamal
that organs and tissue does mesoderm create
muscles, cost of skeletal system, circ system, internal repo organs, kidneys and outer walls of digestive tract
what organs and tissue does the endoderms create
lining of digestive tract, liver, pancrease, lining or resp tract, thyroid gland, lining of urethra, urinary bladder
neulation of vertebrates
-neural plate forms as a thickened region of ectoderm along the dorsal midline of the embryo
-the centre of the neural plate sinks and the edge elevates
-the centre sinks farther down and the edges move together
-the edge fuse together closing the neural tube
-the neural tube pinches free; the ectoderm closes over the tube neural crest cell migrates to many locations in the embryo to become numerous different cell types
key features of stages neurolation
-neural plate formation
-formation of neural tube
-somite formation
neural plate formation:
thickening of ectoderm over notochord forms neural plates, adjacent ectodermal regions form epidermis
formation of neural tube
infolding and pinching off of the neural plate generates the neural tube
somite formation
mesoderm layers flanking the notochord becomes segmented to form block like structure called somites (forms repeated structures like body segments, ribs and vertebrae later development)
organogenesis
-various regions of three germ layers develop into the rudiments of organs, which involves the following process
-localized changes in cell shape, size, number
-cell migration: neural crests (froth germ layer), gives rise to teeth, peripheral nerves, skull, bones, etc
-programmed cells death (apoptosis), pruning of cell when no longer needed
