DAT bio Chapter 12 reproduction and dev bio Flashcards
types of asexual reproduction
binary fission
budding
regeneration or fragmentation
parthenogensis
Binary Fission:
Done by Unicellular organisms
(prokaryotes and the mitochondria and
chloroplasts of eukaryotes). DNA is replicated,
migrates to opposite ends of the cell. Septum
forms in the middle and separates, creating
two separate cells.
Budding:
(outgrowth) forms on the
organism. DNA is replicated and deposited into
bud, which buds off, eg. hydra, yeast.
Regeneration or fragmentation:
piece of
organism breaks off. Can regenerate broken
piece or sometimes a new organism can
grow from a fragment, eg. hydra, flatworms.
Parthenogenesis:
unfertilized egg develops
to a viable organism, eg. Honeybees exhibit
haplodiploidy (males haploid, females
diploid).
Spermatogonia undergo ____ meiotic divisions
to become _____- and differentiate into
sperm.
2
spermatids
where is the Site of spermatogensis (sperm production)
Step 1 of spermatogensis
Seminiferous tubules of testes
Seminiferous tubules of testes contain
● Sertoli cells: activated by follicle stimulating hormone (FSH). Surround and nourish sperm. Produce inhibin (inhibits FSH - negative feedback). ● Spermatogenic cells: produce spermatozoa.
Where is sperm (not matured) transported
Step 2 of spermatogensis
transported using peristalsis to epididymis for maturation and storage
Step 3 of spermatogenesis
Sperm moves through vas deferens (group
of tubules) to ejaculatory duct (where vas
deferens meets seminal vesicles) which
propels sperm into urethra and leads to
ejaculation out of penis as semen (sperm +
accessory gland secretions).
Mnemonic for spermatogenesis
Mnemonic (SEVEn UP): Seminiferous tubules →
Epididymis → Vas Deferens → Ejaculatory Duct →
Urethra → Penis.
Sperm structure
● Head: contains nucleus and acrosome
● Midpiece: mitochondria (ATP production).
● Tail: long flagellum (microtubules) to
propel sperm.
Accessory glands
Seminal Vesicles:
Prostate Gland:
Bulbourethral Glands:
seminal vesicles
Contains secretions containing fructose which provides sperm with nutrients to produce atp. Also produce viscous mucus that (cleans and
lubricates urethra), and also secrete prostaglandins
(causes urethral contractions which propels
sperm).
prostate glands
Makes the sperm more alkaline(basic) so that the sperm can survive the acidity of the female reproductive tract
bulboutrethral glands
viscous mucus (cleans and lubricates urethra).
Hormones in males
- Follicle Stimulating Hormone (FSH):
stimulates sperm development in seminiferous
tubules. - Luteinizing Hormone (LH): stimulates Leydig
cells to produce testosterone. - Testosterone: matures sperm, gives rise to
male secondary sex characteristics.
Where is eggs produced?
ovary
eggs travel through what to the uterus?
fallopian tube or the oviduct
Where is egg fertilized
uterus
uterus has 3 layers
perimetrium
(outer), myometrium (middle, smooth
muscle), endometrium (inner epithelial, lined
by mucous membranes).
what is the narrow opening of the uterus that leads to the vagina
cervix
what is the vagina
opens to external environment (where
sperm enters and birth occurs).
Oogenesis step 1
Many oogonia produced, majority die via apoptosis, small fraction remain and differentiate to primary oocytes (begin meiosis but are arrested in prophase I until puberty).
Oogenesis step 2
At puberty: one egg per month ovulates,
completing meiosis I, which produces a large
secondary oocyte (arrested in meiosis II
during metaphase II) and a polar body.
Oogenesis step 3
If fertilization occurs: meiosis II is completed.
Oogenesis step 4
At the end of meiosis II: 2-3 polar bodies
(non-viable) and 1 oocyte (viable, contains
majority of cytoplasm and nutrients for fetus)
are produced.
Hormones in females
- Follicle Stimulating Hormone (FSH):
stimulates follicles in ovary to develop and
production of estrogen and progesterone. - Luteinizing Hormone (LH): stimulates
ovulation of egg, corpus luteum formation,
which produces estrogen and progesterone. - Estrogen and Progesterone: menstrual cycle
and reproduction, give rise to female secondary
sex characteristics.
Menstrual cycle part 1
Follicular phase
hypothalamus releases
Gonadotropin Releasing Hormone (GnRH)
→ anterior pituitary releases LH and FSH →
FSH binds to the ovaries and induces follicles
to develop → developing follicles release
estrogen → endometrium thickens → rapid
LH spike → ovulation.
Menstrual cycle part 2
ovulation
Ovulation: Ovulation (egg is released from
Graafian follicle) → fimbriae on oviduct
catches egg, cilia sweep egg into oviduct →
egg travels down oviduct (awaiting sperm
fertilization).
Menstrual cycle part 3
Luteal phase
follicle develops into the corpus luteum (maintained by FSH and LH) → corpus luteum produces progesterone and some estrogen → uterine lining thickens (prepares for implantation).
Menstrual cycle part 4
if no implantation occurs
LH and FSH levels drop (due to hypothalamus and pituitary inhibition by increased progesterone and estrogen) → corpus luteum can no longer be maintained → progesterone and estrogen levels drop (hypothalamus and pituitary are not inhibited anymore) → endometrium sloughs off (menstruation) → cycle repeats.
Menstrual cycle part 5
If implantation occurs
outer layer of placenta produces Human Chorionic Gonadotropin (HCG) → maintains corpus luteum → progesterone and estrogen levels maintained → endometrium remains (no menstruation).
Hormone feedback loops
2 types
positive and negative
positive feed back loops does what
stimulate a pathway to
increase production.
Positive feedback loops stimulate a pathway to
increase production of lactation and childbirth
● Lactation: Infant suckling increases prolactin production which causes lactation (milk production) and further increases infant suckling. Oxytocin releases milk (milk let down reflex). ● Childbirth: Oxytocin induces contractions which push the baby out of the womb. The baby pushes against a nerve in the cervix that signals the hypothalamus and pituitary to release more oxytocin.
Negative feedback loops does what
inhibit a pathway to
decrease production.
Negative feedback loops inhibit a pathway and it causes the
The hypothalamus releases GnRH causing the pituitary to release FSH and LH which increase testosterone levels. High testosterone levels inhibit the hypothalamus from releasing GnRH, lowering FSH and LH and testosterone. ● The same occurs with estrogen and progesterone in the menstrual cycle.
What is fertilzation
the joining of a haploid sperm and
a haploid egg to form a diploid zygote.
Structure of egg
Outermost layer, corona radiata (jelly coat,
made of follicular cells), nourishes developing egg.
Underneath is the vitelline layer (zona pellucida
in mammals), made of glycoproteins. Plasma
membrane is under the zona pellucida.
What is the final maturation step for sperm prior to fertilization
(capacitation) It is Triggered by
secretions in uterine wall. Destabilizes sperm
plasma membrane proteins and lipids
resulting in:
● Preparation of sperm tip for acrosomal
reaction.
● Increased calcium permeability causing a
hyperactive state (flagella beats harder,
sperm swims faster).
What is acrosomal reaction?
recognition process
between sperm and egg before fusion.
Ensures same-species fertilization.
What happens in acrosomal reaction?
Sperm
goes through the corona radiata to reach
zona pellucida. Actin from sperm binds to
ZP3 protein of egg’s zona pellucida (mutual
recognition). Membranes of sperm head and
acrosome fuse, releasing hydrolytic
acrosomal enzymes to digest zona pellucida
and allow sperm to fuse with plasma
membrane of egg (fertilization).
what is polyspermy block?
prevents polyploidy by
inhibiting polyspermy (multiple sperms
penetrating egg).
2 types of polyspermy block
● Fast block occurs first when sodium ions
diffuse into the egg, depolarizing its
membrane and prevents sperm binding.
● Slow block: gradual, long-lasting occurs
second. Calcium ions released in egg
stimulate cortical reaction (exocytosis of
cortical granules). Cortical granules
make zona pellucida impenetrable and
stimulate proteases to separate zona
pellucida from plasma membrane.
What happens at completion of meiosis 2 for the secondary oocyte>
During meiosis II, the egg is arrested
in metaphase. After penetration, meiosis in
the secondary oocyte continues creating a
haploid oocyte and producing a second
polar body.
2 types of zygote formation
● Monozygotic twins: identical twins. One
zygote splits. Two embryos with identical
genetic material.
● Dizygotic twins: fraternal twins. Two
separate eggs fertilized by two separate
sperms. Two zygotes with different
genetic material.
What is cleavage?
is rapid cell division without changing
the total mass of cells. The subsequently smaller
cells resulting from cleavage are called
blastomeres.
2 axis of cleavage
● Radial Cleavage: cells aligned in vertical
axis (eg. deuterostomes).
● Spiral Cleavage: misaligned cells, deviate
from axis (eg. protostomes).
Fate of cells have two cleavages
● Determinate (or mosaic) Cleavage: blastomeres have decided fate. ● Indeterminate (or regulative) Cleavage: blastomeres do not have pre-set fate.
What is evenness of embryo division
holoblastic cleavage
meroblastic cleavage
What is holoblastic cleavage
throughout entire embryo, evenly divides embryo, in animals with little yolk (eg. humans, sea urchins). ○ Exception: Frogs have lots of yolk and also undergo holoblastic cleavage that is uneven (exhibit polarity).
what is meroblastic cleavage?
Cleavage: partial cleavage, embryo not evenly divided, in animals with lots of yolk (eg. birds, fish, reptiles). Exhibits polarity with animal pole (active cleavage) and vegetal pole (mainly yolk, negligible division).
what is morula ( embryogenesis in mammals
(ball of blastomeres): forms at 12-16 cell
stage.
What happens at 128 cell stage
Blastula stage (hollow cavity) begins to form in the center of the sold mass of dividing cells, known as the blastocoel.
Blastocyst stage:
cells of blastula divide and
differentiate to form:
The cells of the blastula will divide and differentiate into what two structures
trophoblast
inner cell mass
Trophoblast (outer ring of cells)
● Forms chorion (extraembryonic membrane) - support embryo. ● Implants embryo in the uterus. ● Produces HCG (maintains corpus luteum and endometrium).
Inner Cell Mass (ICM)
forms embryo and
three other extraembryonic membranes
(amnion, yolk sac and allantois).
inner cell mass differentiates into what two layers
● Hypoblast: partially contributes to yolk
sac, remainder degenerates via apoptosis.
● Epiblast: contributes to main embryo.
Cells thicken to form primitive streak
which defines left-right and top-bottom
axes and is crucial for gastrulation to
begin.
Fertilization occurs in the ____, cleavage
occurs as ______ travels to the uterus. At
the uterus, fertilized egg is at ______.
To implant in uterine wall, blastocyst undergoes
_______. Trophoblasts replace _____ and implantation can occur.
oviduct fertilized egg blastocyst stage zona hatching zona pellucida
What is gastrulation?
formation of a trilaminar
embryo. Epiblast cells invaginate inwards through
the primitive streak to form three germ layers:
endoderm, mesoderm, ectoderm. Embryo is
now at the gastrula stage.
As cells invaginate they create an opening called the \_\_\_\_\_\_, which forms the \_\_\_\_\_\_\_\_ (center cavity - becomes digestive tract).
blastopore
archenteron
Ectoderm (outer germ layer) forms
● CNS (brain and spinal cord) and PNS. ● Sensory parts of ear, eye, and nose. ● Epidermis layer of skin, hair, and nails. ● Mammary and sweat glands. ● Pigmentation cells. ● Enamel of teeth.. ● Adrenal medulla.
Mesoderm (middle germ layer) forms:
● Bone and skeleton. ● Muscles. ● Cardiovascular system. ● Gonads. ● Adrenal cortex. ● Spleen. ● Notochord (induces spinal cord formation from ectoderm).
Endoderm (inner germ layer) forms:
● Epithelial lining of digestive, respiratory,
and excretory systems.
● PLTT (Pancreas, liver, Thyroid and
parathyroid. Thymus).
Organogenesis
formation of new organs.
What is nervous system development called
neurulation
Neurulation is nervous system development: An
______ at this stage is known as a _______.
embryo
neurula
Neurulation is nervous system development step 1
Notochord stimulates ectoderm to thicken,
forming the neural plate.
Neurulation is nervous system development step 2
Neural plate folds onto itself forming the
neural fold / neural groove.
Neurulation is nervous system development step 3
Neural fold continues to fold, forming a
hollow tube (neural tube).
● Some cells roll off to form neural crest
cells (migrate to form teeth, craniofacial
bones, skin pigmentation, etc.).
Neurulation is nervous system development step 4
4. Neural tube differentiates into CNS. Mesoderm cells (somites) form two masses alongside notochord. Becomes vertebrae and skeletal muscles associated with axial skeleton.
What are stem cells
undifferentiated cells with
potential (potency) to become many types of
cells.
Stem cells become what kind of cells
totipotent
pluripotent
mnultipotent
totipotent
stem cells can become any cell
eg. zygote, blastomeres of morula
pluripotent
stem cells can become any of of
the 3 germ layers (eg. ICM cells → embryonic
stem cells).
Multipotent
stem cells can only differentiate
to a few cell types of a specific tissue type (eg.
hematopoietic stem cell → many blood cells).
What is extraembryonic development
Development of structures outside the embryo.
Provide protection and nourishment to fetus.
Placental mammals have _____
while egg-laying animals such as reptiles, birds,
and monotremes (egg-laying mammals) lay eggs.
______- are mammals that carry their babies
in a pouch.
internal pregnancies
marsupials
What is amnion
Extraembryonic membranes
innermost layer, membrane around embryo secretes amniotic fluid (water cushion, protecting embryo). ● Amniotes (reptiles, mammals, birds) have an amnion, anamniotes (amphibians, fish) do not (surrounding water serves as cushion).
what is Chorion:
Extraembryonic membranes
outermost layer. ● Placental mammals: forms fetal half of the placenta (platform for exchange of gases, nutrients, and waste). ● Egg-laying animals: membrane for gas exchange just underneath egg shell.
What is Allantois:
Extraembryonic membranes
sac that buds off of the archenteron. Stores waste for disposal. ● Placental mammals: transports waste to placenta, becomes the umbilical cord, and in adults forms urinary bladder. ● Egg-laying animals: initially stores uric acid, later fuses with chorion (helps with gas exchange).
what is Yolk Sac:
Extraembryonic membranes
contains yolk (intraembryonic,
provides nutrients).
● Placental mammals: transient function
until placenta develops. First site of blood
cell formation.
● Egg-laying animals: sole player in providing
nutrients.
What happens in frog embryo
Lots of yolk, Uneven holoblastic cleavage with
animal pole (darker colour) and vegetal pole
(paler). Gray crescent is opposite to the site of
sperm entry. Forms due to cytoplasm rotation,
causing mixing from the two poles. Any cell from
the first cleavage that receives a bit of the gray
crescent can become a full frog embryo. Frog
embryos have no primitive streak. Instead,
gastrulation begins at the dorsal lip of
blastopore (forms at site of gray crescent).
What happens in chick embryo
Model for all egg-laying animals. Embryo has no
direct connection to mother and needs large
yolk for nutrients. Chalaza connects yolk to ends
of shell (allows nutrient distribution to entire
embryo). Chicks have a primitive streak.
Blastodisc (analogous to ICM in mammals) is
flattened resulting in an elongated blastopore
upon gastrulation at primitive streak.
Factors influencing development
embryonic induction
homeotic genes
egg cytoplasm determinant
apoptosis
Embryonic Induction:
Organizers secrete chemicals that
influence what neighboring cells become
in the future (eg. dorsal lip of blastopore
in frogs).
Homeotic genes:
Master controller turns different gene expressions on / off. A Homeobox is a common sequence containing homeotic genes homologous across organisms (~180 nucleotides). Crucial in animal development. Ex. HOX genes.
Egg Cytoplasm Determinant:
If egg cytoplasm is unevenly distributed
(creating animal and vegetal poles), an
axis is created, influencing how the
embryo divides during cleavage.
Apoptosis:
Programmed cell death important for
normal development of fetus (eg.
removing webbing between fingers) and
adults (preventing cancer).
