animal reproduction & development Flashcards
Sexual reproduction
a type of reproduction in which 2 parents give rise to offspring that have unique combinations of genes inherited from both parents via the gametes
Asexual reproduction
the generation of offspring from a single parent that occurs without the fusion of gametes
- in most cases, the offspring are genetically identical to the parent
Parthenogenesis
a form of asexual reproduction in which females produce offspring from unfertilized eggs
Dioecious
having the male & female reproductive parts ON DIFFERENT individuals of the same species
Monoecious
having both the male & female reproductive organs IN the SAME individual; hermaphrodite.
Hermaphrodite
an individual that functions as both male & female in sexual reproduction by producing both sperm & eggs
Protandry
fish that function as a male and later as a female; and.
Protogyny
fish that function as a female and later as a male
Gametogenesis
the process by which gametes are produced
Spermatogenesis
the continuous & prolific production of mature sperm cells in the testis
Oogenesis
the process in the ovary that results in the production of female gametes
Isolecithal
SPARSE EVENLY distributed yolk, eg., sea urchin, mouse.
Mesolechithal
MODERATE amount of yolk, often UNEVENLY distributed, eg., frog.
Telolecithal
DENSE yolk concentrated AT one end, eg., bird, reptile.
Fertilization
the fusion of egg & sperm (this event marks the beginning of fertilization)
Spermatophore
or sperm ampulla is a CAPSULE or MASS containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female’s ovipore during reproduction.
Copulatory organ
An organ utilized by the male animal for insemination, that is, to deposit spermatozoa directly into the female reproductive tract.
Acrosome
FRONT part of the sperm cell which RELEASES a bunch of ENZYMES & BREAKS down the barrier allowing access for the sperm to reach the cell membrane of the egg
Polyspermy
multiple sperm entering the egg
Fertilization envelope
a RESISTANT membranous layer IN EGGS of many animals that forms FOLLOWING FERTILIZATION by the thickening and separation of the vitelline membrane from the cell surface and that PREVENTS multiple fertilization.
Oviparity/oviparous
referring to a type of development in which young hatch from eggs LAID OUTSIDE the mother’s body
Ovoviviparity/ovoviviparous
referring to a type of development in which young hatch from eggs that are RETAINED in the mother’s uterus
Viviparity/viviparous
referring to a type of development in which the young are born alive AFTER having been NOURISHED in the uterus by blood from the placenta
Cleavage
the succession of RAPID CELL DIVISIONS without significant growth during early embryonic development that CONVERTS the ZYGOTE to a BALL OF CELLS
Gastrulation
in animal development, a series of cell & tissue movements in which the blastula-stage embryo folds inward, producing a 3-layered embryo, the gastrula
Neurulation
refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube.
- The embryo at this stage is termed the neurula.
- neural plate –> neural tube –> brain & spinal cord
Organogenesis
the process in which organ rudiments develop from the 3 germ layers after gastrulation
Compare sexual & asexual reproduction
- in sexual reproduction, the fusion of HAPLOID gametes FORMS a DIPLOID cell, the zygote
- the animals that develops from a zygote can in turn give rise to gametes by MEIOSIS
- asexual reproduction is the generation of new individuals WITHOUT the fusion of egg & sperm
- in most asexual animals, reproduction relies entirely on MITOTIC cell division
Identify examples of each (sexual & asexual reproduction)
sexual: ex: - humans - cnidarians (medusa) - echinoderms - chordates - playhelminthes - molluscs - annelids (hermaphroditic) - brachiopoda - nematodes - arthropods
asexual:
ex:
- cnidaria (polyps)
- hydra
- platyhelminthes (hermaphroditic)
- annelids (fragmentation)
- poriforea
- tunicates
- hymenoptera - bees, ants, wasps
- echinoderms
- chordates(parthenogenesis)
- arthropods (parthenogenesis)
Explain the advantages & disadvantages of both modes (sexual & asexual reproduction)
sexual:
- UNIQUE combinations of parental genes formed during meiotic recombination & fertilization
- by producing offspring of VARIED GENOTYPES, sexual reproduction may enhance the reproductive success of parents when environmental factors, such as pathogens, change relatively rapidly
- BENEFICIAL gene combinations arising through recombination might SPEED UP adaptation
- advan. is significant only when the rate of beneficial mutations is HIGH & population size is SMALL - shuffling of genes during sexual reproduction might allow a population to RID ITSELF of sets of harmful genes more readily
ALTHOUGH:
- sexual is expensive in that it results in fewer potential offspring than asexual reproduction
asexual:
- is expected to be most advantageous in stable, favourable environments b/c it perpetuates successful genotype faithfully & precisely
- species prosper in (perhaps temporary) environmental niches
Explain the 3 discussed mechanisms of parthenogenesis in animals
- results in genetic clone
- looks like sexual reproduction, but there isn’t any sex involved, eggs are laid & then eggs become new individuals WITHOUT becoming fertilized
EX: in hymenoptera - bees, ants, wasps)
- diploid queen –> haploid drone (haploid egg) - very rate parthenogenesis (in honey bees)
- chromosome duplication!
- no father!
diploid queen –> diploid queen (from haploid egg)
Contrast monoecious & dioecious species
monoecious:
having both the male & female reproductive organs in the same individual; hermaphrodite.
EX: porifera, flatworms, annelids etc.
dioecious:
having the male & female reproductive parts on different individuals of the same species
EX: brachiopods (reproduce sexually), nematoda, arthropods etc.
Describe the sexes within these species based on type of gonads present & gametes formed
female:
- eggs, which provide the initial food stores for the embryo, are typically much larger & carry out their function within the female reproductive system
- there they must mature in synchrony with the tissues that will support the embryo
- the reproductive system of the human female consists principally of the LABIA and the GLANS of the CLITORIS externally & the VAGINA, UTERUS, OVIDUCTS, & OVARIES internally
- EGGS are produced in the ovaries & upon fertilization develop in the uterus
male:
- sperm are small & motile & must pass from the male to the female
- in human males, SPERM are produced in TESTES, which are suspended outside the body in the SCROTUM
- ducts connect the testes to internal accessory glands & to the PENIS
Compare gametogenesis (location, duration, ploidy, etc.) in mammalian males & females
female:
- oogenesis, the development of mature oocytes (eggs), is a prolonged process in the human female
- immature eggs form in the ovary of the female embryo but DO NOT complete their development until years, & often decades, later
male:
- spermatogenesis, the formation & development of sperm, is continuous & prolific in adult males
- cell division & maturation occur throughout the seminiferous tubules coiled within the 2 testes
Explain the process of fertilization
- sperm dissolve or penetrate any protective layer surrounding the egg to reach the plasma membrane
- molecules on the sperm surface bind to receptors on the egg surface, helping ensure that a sperm of the same species fertilizes the egg
- changes at the surface of the egg PREVENT polyspermy, the entry of multiple sperm nuclei into the egg
- if polyspermy were to occur, the resulting abnormal number of chromosomes in the embryo would be lethal
Describe the mechanisms that prevent multiple sperm from fusing with a single egg
changes at the surface of the egg PREVENT polyspermy, the entry of multiple sperm nuclei into the egg
- if polyspermy were to occur, the resulting abnormal number of chromosomes in the embryo would be lethal
- FAST polyspermy block
- SLOW polyspermy block
Contrast external & internal fertilization
- in species with EXTERNAL fertilization, the female releases eggs into the ENVIRONMENT, where the male then fertilizes them
- other species have INTERNAL fertilization: sperm are deposited IN or NEAR the female reproductive tract, & fertilization occurs within the tract
Compare oviparity, ovoviviparity & viviparity
oviparity/oviparous: some species of sharks; they lay eggs that hatch OUTSIDE the mother’s body
- these sharks release their eggs after encasing them in protective coats
ovoviviparity/ovoviviparous: other species of sharks; they RETAIN the fertilized eggs in the oviduct
- nourished by the egg yolk, the embryos develop into young that are born after hatching within the uterus
viviparity/vivparious: a few shark species; the young develop within the uterus & OBTAIN NOURISHMENT PRIOR to birth by receiving nutrients from the mother’s blood through a yolk sac PLACENTA, by absorbing a nutrients fluid produced by the uterus, or by eating other eggs
Explain the advantages & disadvantages of each (oviparity, ovoviviparity & viviparity)
Oviparity (egg bearing) is when the embryo is in an egg in the open environment when it is developing.
- It is BENEFICIAL to parents because they DO NOT need to stay with their eggs (although some do) and they can possibly have separate food needs after the child is born or if they have the same food needs, can live separately so they do not compete.
The trade-off is that the young are LESS LIKELY to SURVIVE predator attacks, deadly temperature changes, and other environmental issues that may arise.
Ovoviviparity (offspring develops in mother’s body but is surrounded by a yolk)
- is good because the embryo develops from yolk for its nutrients and DOES NOT DEPEND on the mother so it takes less energy than viviparity to grow the young. But there is still temperature regulation that keeps the young in a better environment.
- The drawback is the trade off of producing more young.
Viviparity (give birth to live young)
- is good because the embryo can develop inside the mother WHERE TEMPERATURES and NUTRIENTS ARE STABLE, thus enabling the young a greater chance to survive. This is especially true in cold weather.
- The disadvantage is that it TAKES MORE ENERGY for the mother and thus CANNOT PRODUCE as many young in her life.
Describe the major events that occur during gastrulation
- 1st few divisions in cleavage occur in the fallopian tubes as the cell is actually heading to the uterus (where it embeds), the sperm finds its way up there & fertilizes
- will bind to UTERINE LINING (ENDOMETRIAL EPITHELIUM)
- the INNER CELL MASS is what will become the embryo basically
- trophoblast basically will become the placenta, it will bind to uterine lining, invade the uterine lining, find blood vessels within the uterus & become the placenta as the embryo is developing - trophoblast is expanding into the uterine tissue finding blood vessels & eventually completely interwinds with blood vessels making an exchange system
- another countercurrent exchange system where gases & various nutrients & things will pass back & forth b/t the maternal blood & the new blood vessels that will eventually head out that direction to the placenta from the embryo/fetus actually
- inner cell mass divides into the epiblast & hypoblast & the epiblast will become most of the embryo - following implantation, the trophoblast continues to expand into the endometrium, & 4 new membranes appear: allantois, aminon, chorion, & yolk sac
- although these extraembryonic membranes are formed by the embryo, they enclose specialized structures located outside the embryo
- as implantation is completed, gastrulation begins
- cells move inward from the epiblast through a primitive steak & form mesoderm & endoderm, just as in the chick - eventually gastrulation occurs, epiblast, there is a primitive steak & cells will flow in from the outside & form the endoderm & the mesoderm & cell division resumes, there is a yolk (small & gets smaller & smaller) b/c placenta will feed embryo
Illustrate the process of neurulation in chordates
- beings as cells from the dorsal mesoderm come together to form the NOTOCHORD (the rod that extends along the dorsal side of the chordate embryo)
- signalling molecules secreted by these mesodermal cells & other tissues induce the ectoderm above the notocord to BECOME the NEURAL PLATE
- next, the cells of the neural plate change shape, curving the NEURAL PLATE INWARD
- in this way, the neural plate ROLLS itself into the NEURAL TUBE, which runs along the anterior-posterior axis of the embryo
- the neural tube will become the BRAIN in the head & the SPINAL CORD along the rest of the body
What is mitosis?
regular cell division, i.e. for growth & development
- DNA is duplicated before the cell divides
- results in 2 daughter cells with the SAME # of chromosomes as the parent cell
- i.e. 2 DIPLOID cells (2n) with identical DNA
What is meiosis?
cell division for sexual reproduction, i.e. gamete production
- DNA is duplicated, then the cell divides
- then the daughter cell ALSO divides
- results in 4 cells with HALF the # of chromosomes
- i.e. 3 HAPLOID gametes (n) with shuffled DNA
What are 4 asexual reproductions that results in genetic clone?
- budding
- fission
- fragmentation
- parthenogenesis
What is budding?
- where a baby just literally grows off the side of it & gets bigger & eventually falls off
- will have EXACT same genetics as you do b/c it is growing off of you - mitosis
- results in genetic clone
- asexual reproduction
Which phyla does budding?
cnidaria
- hydras primary method of reproduction is budding
Which phyla reproduces asexually & sexually?
cnidaria (also reproduce with sperm & egg in water)
What is fission?
you BREAK in HALFanimal splits in half/radial things close off, pinch off & then break apart & now their are 2 of them
- results in genetic clone - mitosis
- asexual reproduction
Which phyla does fission?
cnidaria
What is fragmentation?
BREAKING an animal apart into tiny pieces & it lands on the ground or food or water & other animals consume them & the little pieces grow up into new worms
- results in genetic clone - mitosis
- asexual reproduction
Which phyla does fragmentation?
platyhelminthes, also cnidaria, annelids, porifores, & even tunicates
What is parthenogenesis?
looks like sexual reproduction but there isn’t any sex involved, eggs are laid & then eggs become new individuals without becoming fertilized
- results in genetic clone - mitosis
- asexual reproduction
Which phyla does parthenogenesis?
hymenoptera - bees, ants, wasps
There is a very rate parthenogenesis (in honey bees) where there is chromosome duplication and results in…
no father!
and only female offspring!!
What are the 2 forms of sexual reproduction?
- paired hermaphrodites
2. lone hermaphrodites
What is a hermaphrodite?
has male & female parts
What is paired hermaphrodites?
male part of one impregnants the female part of the other & vice versa & then both go away pregnant & both lay eggs
What are examples of paired hermaphrodites?
terrestrial molluscs
- lychees, slugs, snails etc
What is lone hermaphrodites?
eggs produced & sent to middle, sperm is produced & sent to middle & they meet in the middle & impregnant itself & lays a fertilized egg (diploid)
- although they can mate in pairs (with male) too
What are examples of lone hermaphrodites?
C. elegans
- have a male & female end
What are the types of gametogenesis?
spermatogenesis (making of male gamete sperm) & oogenesis
Meiosis happens CONTINUALLY in adult male humans…
hundreds of millions of new sperm per day
How many weeks does it take sperm to develop in seminiferous tubules (with the help of Sertoli cells, or “nurse cells”)
7 weeks
After maturation of sperm, where does it exit?
seminiferous tubules via lumen
How many weeks does it take the sperm to travel through epididymis (grows a tail)?
3 weeks
When does all prophase 1 happen for oogenesis?
prior to birth - then meiosis halts until puberty
What happens once a month for females?
1 primary oocyte (within a follicle) completes meiosis 1
Meiosis II halts metaphase because…
secondary oocyte awaits penetration by sperm
What is the result right after meiosis II during females cycle?
meiosis II completes resulting in a mature egg (with the head of a sperm cell already within)
What event marks the beginning of fertilization?
the fusion of egg & sperm
- the fusion of egg nucleus & the sperm nucleus occurs later during fertilization
- immediately after egg & sperm fuse, egg undergoes changes to prevent polyspermy
Why is polyspermy important?
b/c if you have more than 1 sperm entering the egg you have too many chromosomes (if you have 3 sets of chromosomes the egg will die)
What is the acrosomal reaction?
enzymes released from acrosome to digest egg’s jelly coat
What is the conspecific recognition?
acrosomal process extends to bind to receptor molecules on egg’s surface
What is the fertilization process in sea urchins?
- ACROSOMAL REACTION: enzymes released from acrosome to digest egg’s jelly coat
- acrosomal process extends to bind to RECEPTOR molecules on egg’s surface (CONSPECIFIC RECOGNITION)
- egg & sperm membranes FUSE
- sperm nucleus ENTER egg
- fast polyspermy block
- slow polyspermy block (“cortical reaction”)
- egg ACTIVATION occurs
What is the FAST polyspermy block?
fast method of preventing additional sperm from entering the cell
- immediately after penetration, egg DEPOLARIZES
- prevents other sperm cells from penetrating (COMING IN)
- SHORT-lived reaction
What is depolarization?
resting membrane potential; so sodium channels open, sodium is positively charged & there are relatively low amounts of it in the cell, so it floods into the egg, raising the voltage inside the egg compared to outside the egg, & this CHANGE IN VOLTAGE PREVENTS other sperm cells from penetrating the egg
What is the SLOW polyspermy block (“cortical reaction”)?
comes on while the depolization is active; so once 1 sperm cell gets in the voltage jumps up real fast, initially preventing other sperm from getting in & then the cortical granule binds to the cell membrane & pushes out the outer membrane which then hardens & now its imperianous to new sperm cells (so no new sperm cells can get in)
- CORTICAL GRANULES (vesicles) FUSE with MEMBRANE
- VITELLINE LAYERS PUSHED AWAY from membrane
- VITELLINE LAYERS HARDENS into FERTILIZATION ENVELOPE
- prevents penetration of additional sperm
What is egg activation?
sudden increase in metabolic activity getting egg ready for cleavage
How does the fertilization differ from sea urchins for mammals?
like sea urchins, but
- sperm also must pass through follicle cells
- jelly coat is called ZONA PELLUCIDA
- NO fast block to polyspermy
- fertilization much slower (often>24h) compared to 90 mins in sea urchins
What is cleavage?
means to divide/separate; cell division (cell in 2)
- the 1st cell division marks the end of fertilization; and the beginning of the cleavage period
- species undergo either holoblastic (complete) or meroblastic (incomplete) cleavage
What is holoblastic cleavage?
- each cell divides completely each time
- sparse yolk left in each cell
- several types:
- bilateral
- radial
- rotational
- spiral
Apart of the holoblastic cleavage, which phyla have the RADIAL type?
- echinoderms
- amphibians
- lampreys
Apart of the holoblastic cleavage, which phyla have the ROTATIONAL type?
- placental mammals
2. marsupials
What is meroblastic cleavage?
- large amounts of yolk
- so the cleavage just can’t occur (when the cell is dividing there is just too much yolk in the way it can’t split all of that up easily into 2 cells)
- several types:
- bilateral
- discoidal
- superficial
What do the meroblastic cleavage do instead, because of the large amount of yolk?
they just go partly through, one end of it where there is not much yolk divides & the other end just sits there kinda complete or whole & most of the yolk is left behind & doesn’t get chopped up at all
Apart of the holoblastic cleavage, which phyla have the DISCOIDAL type?
most fishes, reptiles, monotremes
Apart of the holoblastic cleavage, which phyla have the SUPERFICIAL type?
insects
What is the common feature of all of the discoidal animals (most fishes, reptiles, monotremes)
all lay eggs
- they lay an egg that has to be pretty independent & it has to feed on yolk for much longer period of time than other animals (so they have HUGE amounts of yolk, in order to feed the embryo all through embryotic development)
Why do placental animals just have a tiny amount of yolk?
b/c it only has to feed the embryo long enough for it to get implanted in the uterus & then it is feed into the placenta from the mother
Radial cleavage, in echinoderms have…
small amounts of yolk, evenly distributed among cells
Radial cleavage, in amphibians have…
moderate amount of yolk, largely concentrated at vegetal pole
Why does the animal portion have much smaller cells than the vegetal portion of AMPHIBIANS?
b/c they have a lot of yolk in them
- yolk concentrated more in vegetal hemisphere opposed to animal hemisphere
Rotational cleavage, in mammals (except monotremes) have…
small amounts of yolk, evenly distributed among cells
What is the BENEFIT to ROTATIONAL compared to RADIAL cleavage?
for radial:
- all the cells have a predetermined fate from the very beginning & there is no room for subsitution (so if you took out a cell from it, you would end up removing a significant chunk of the entire animal & its probably not going to survive b/c all of the cells already have some designated job & they can’t redesign themselves)
rotational:
- more randomly looking, doesn’t have clear boundaries as top or bottom b/c it is rotating at least early on, so if you took a cell out, the embryo will probably be just fine b/c some other cell would take its place b/c they haven’t figured out who is doing what yet
so BASICALLY, rotational is more beneficial b/c it allows for some flexibility, during development & this doesn’t work if you have a lot of yolk
Discoidal cleavage, in monotremes, reptiles, & most fishes…
large amount of yolk at vegetal pole
- so, the 1st division can’t really cut through the entire yolk, it is just too huge, so cell divisions just occur basically adjacent to the yolk
Superficial cleavage, in most insects…
- NUCLEI divide rapidly long before the rest of the cell
- yolk forms in middle, after cells begin to divide
- eventually when they are there are a large amount of nuclei they all go to the outer edge of embryo & they start forming cell membranes & they start making actual new cells & the middle remains as yolk
- then all the cells on the outside can feed from yolk as the inside develops
What is unique about superficial cleavage (in most insects)
- tons of MITOTIC division
- NO cell divisions
- NO cytokenesis
Gastrulation in chicks
- the starting point for gastrulation in chicks is an embryo consisting of a layer of cells, the BLASTODERM, divided into upper & lower layers-the EPIBLAST & HYPOBLAST-lying atop a yolk mass
- all the cells that will form the embryo come from the epiblast
- during gastrulation, some epiblast cells move toward the midline of the blastoderm, detach, & move inward toward the yolk
- the pileup of cells moving inward at the blastoderm’s midline produces a thickening called the PRIMITIVE STEAK
- although the hypoblast contributes no cells to the embryo, it is required for normal development & seems to help direct the formation of the primitive steak before the onset of gastrulation
- the hypoblast cells later segregate from the endoderm & eventually form part of the sac that surrounds the yolk & also part of the stalk that connects the yolk mass to the embryo
Failure to close the neural tube at rostral (head) end is…
lethal
Failure to close at caudal (tail) end leads to…
spina bifida (no function in legs)
What are the mechanisms of morphogenesis?
- differential cell divisions
- different rates of cell division
- asymmetric cell division - changes in cytoskeletal organization
- microtubules
- actin filaments - cell migration
- following chemical signals
- using cytoskeletal changes
apoptosis (programmed cell death)
What is apoptosis?
programmed cell death
- where some cells are designed for some kind of purpose like getting a signal, releasing signal molecules then done, so once that is done it just dies
What are the 3 significant ways that Spermatogenesis differs from Oogenesis?
- only in spermatogenesis do ALL 4 products of meiosis develop into mature gametes
- in oogenesis, cytokinesis during meiosis is UNEQUAL, with almost all the cytoplasm separated to a SINGLE daughter cell (this large cell is destined to become the egg; the other products of meiosis, smaller cells called POLAR BODIES, degenerate)
2.
- spermatogenesis occurs THROUGHOUT ADOLESCENCE (puberty) & ADULTHOOD
- during oogenesis in human females, mitotic divisions are thought to be complete BEFORE BIRTH, & the production of mature gametes ceases at about age 50
- spermatogenesis produces mature sperm from precursor cells in a CONTINUOUS SEQUENCE
- whereas oogenesis has LONG INTERRUPTIONS
What is the primitive steak?
a thickening along the future anterior-posterior axis on the surface of an early avian or mammalian embryo, caused by a pilling up of cells as they congregate at the midline before moving into the embryo
- end result is the production of the 3 primitive cell layer
- meso, ecto, endo
What is the difference between the male & female gametes in terms of size & motility?
- the female gamete, the egg, is a LARGE, NONmotile cell
- the male gamete, the sperm, is generally a much SMALLER, MOTILEcell
