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
