platyhelminthes
vertebrate reproduction
Losing an eggshell presents challenges.
The maternal and fetal cells must be kept separate to avoid "rejection". The separation
is established through a cell layer called the syncytiotrophoblast (formed with the help of syncytin) the outermost layer of the placenta pressed up against the uterus forming an impervious wall.
oviparous, viviparous, ovoviviparous
the placenta!
an ancient retrovirus gene mutated, evolving into a gene that codes for syncytin. This protein permits the blastocyst to fuse into the uterine wall...
some retrovirus infected an egg-laying vertebrate, settling in the animal’s egg cells. then that egg was fertilized. The protomammal that was hatched
had copies of that virus’ DNA in all its cells.
Spermatogenesis:
testes
Reproduction
Amniotic eggs evolved over 300 million years ago (small lizards evolved from the amphibious reptiliomorphs Carboniferous geologic period) separating amphibians from reptiles, birds and mammals. Amphibians are restricted to wet environments to keep their eggs moist but the amniotic egg permitted animals to expand on land. Birds evolved a hard calcium carbonate shell on their egg and mammals eliminated the shelled egg in favor of an internal system exhibiting similar embryonic layers within the mother's uterus.
The advantages of the amniotic egg include:
access to terrestrial environments
less competition for pools
decreased predation
echinoderms
endocrine control of oogenesis
Seahorse fathers to provide nutrients to their developing embryos in the form of
fats and calcium which help the embryos to build the bony plates under their skin.
The brood pouch also protects the embryos by secreting antibacterial molecules.
A week before they are released from their brood pouch, the young seahorses
break out of their membraneous coverings and swim about the inside the brood pouch stretching the pouch initiating the release of estrogen which initiates the release of the fry from the pouch.
move from
external fertilization
to
internal fertilization
spermatogenesis oogenesis
Oogenesis
cnidaria
asexual reproduction:
1. mates aren't required
2. fast process with many offspring produced in a short time period
Sexual reproduction:
increase in variation occurring due to
a. crossing over
b. the fusion of gametes.
the egg!
arthropods
chordates
the placenta permits
two mammals to coexist although being genetically very different since half of it is fetal and half maternal.
ovulation - fertilization - implantation
remember from 111...
crossing over occurs when
homologous chromosomes
(chromosomes of the same pair)
are lined up and a part of the chromosomes are traded between the pair so that the two chromosomes still contain the same genes but may have different sequences in the genes.
but first...fertilization
but this is what we think of
when we think chordate...
The seahorse is an ovoviviparous fish.
It exhibits male pregnancy...
The female seahorse deposits eggs into the male seahorse's unique brood pouch where the eggs are fertilized
and spend 24 days developing.
the ovarian and uterine
systems are related
move to sexual reproduction from asexual reproduction
Welcome to Dr. Kate Brilakis' Learning Portal
endocrine control of spermatogenesis
porifera
external fertilization:
* only occurs in the water (fish/amphibians)
* female lays eggs/male sheds sperm over them to fertilize
* many more eggs released than are fertilized or mature
efficiency?
*excess wasted sperm/egg
*more eaten or die due to environment than survive
annelids
external vs internal fertilization
Oogenesis:
ovaries
internal fertilization
the bottom line...
all reproduction strategies serve to:
1. produce a maximum number of surviving offspring
2. ensure the species survives
3. expend the least amount of energy to do both
nematodes
pathology
fish - amphibians - reptiles - aves - mammals
you've heard of blood brain barrier...
remember meiosis?
fertilization (or not...)