Exam 3 Gen Bio Flashcards
Asexual Reproduction
- offspring are genetically identical
- energy efficient
- more sessile species do this
- less genetic diversity
Budding
asex
new individuals form as an outgrowth or buds from bodies of other animals
Regeneration
asex
replacement of damaged tissue or limbs but can also regenerate complete individuals
Parthenogenesis
development of offspring from unfertilized eggs
echinoderms example
as long as a part of the central disc is found in detached portion
it can develop into whole adult animal
(regen)
bees
males develop from unfertilized eggs (haploid) females develop from fertilized eggs (diploid)
(partho)
Whiptail lizards
no males in the species, some females may act as males depending on cyclical hormonal states
Acting as a male during peaks of hormones stimulates release of eggs from ovary in other female
Tardigrades also do this
Sexual Reproduction
Large energy requirements
- Energy is spent mating and caring for offspring instead of feeding
- more diversity
sexual reproduction requires
the joining of two haploid cells to form a diploid individual:
haploid cells
- Genetic diversity come from crossing over in homologous chromosomes and
independent assortment of chromosomes
how are haploid cells made
Gametogenesis – making of gametes
Mating – bringing gametes together
Fertilization – fusing of the gametes
Gametogenesis
- production of gametes
- occurs in gonads
- made from germ cells which develop from early cell divisions
- germ cells migrate to developing gonads where they produce spermatogonia or oogonia
primary spermatocytes and primary oocytes
Spermatogonia and oogonia (diploid) – multiply by mitosis resulting in
after primary mitosis, comes
meiosis, result in haploid cells that mature into sperm and ova
Spermatogenesis
- primary spermatocytes undergo first meiosis to form secondary spermatocyte
- second meiotic division will produce spermatids (4) that remain connected by cytoplasmic bridges
- after further differentiation, they become more like what we know
Oogenesis
- Oocytes immediately enter prophase of first meiotic division
- Developmental arrest happens often at this point and may last for days, months years (until puberty)
- When meiosis resumes, nucleus completes the first meiotic division
- Daughter cells are unequal in size – secondary oocyte and first polar body
- Second meiotic division of secondary oocyte also asymmetrical – one forms haploid ootid, other forms another polar body
- Polar bodies degenerate, only one mature egg remains
Fertilization
the union of sperm and egg
Fertilization results in a single diploid cell - zygote- will then develop into embryo
Complex series of events:
- Sperm and egg recognize each other
- Sperm is activated, letting it gain access to the plasma membrane of egg
- Plasma membranes of sperm and egg fuse
- Egg will then block entry of any other sperm
- Egg will be metabolically activated and stimulated to start development
- Egg and sperm nuclei fuse to create the diploid nucleus of the zygote
cumulus
Mammalian egg surrounded by thick layer
it is a loose assembly of maternal cells in a gelatinous matrix
Zona pellucida or vitelline envelope
Beneath cumulus is a glycoprotein envelope
- Sperm that are activated after entering female reproductive tract are able to penetrate the cumulus and interact with the Zona pellucida
When sperm contacts zona pellucida
a species specific glyco-protein will bind to molecules on the head of the sperm
Binding triggers an acrosomal reaction in sperm – enzymatic reaction that can digest a path through the zona pellucida
polyspermy
fertilization by more than one sperm BAD
Blocks to Polyspermy and Egg activation:
- First response to sperm entry is blockage of entry of any other sperm
- Sperm binding causes release of calcium from endoplasmic reciulum of egg
- Just under the plasma membrane are cortical granules (vesicles) – contain
enzymes and proteins that will dissolve bonds between zona pellucida and plasma membrane - Release of Calcium ions causes release of cortical granules – enzymes will remove sperm binding receptors
- Rise in cytosolic calcium will also activate egg metabolism and signals completion of meiosis – setting the stage for the first cell division
