Download Spermatogenesis and oogenesis both involve mitosis, cell growth

Spermatogenesisandoogenesisbothinvolvemitosis,cell
growth,twodivisionsofmeiosisanddifferentiation
Oogenesis
Oogenesis is the production the egg cell in the ovaries. The
production starts and ends before the birth of the girl:
1. Oogonia cells (cells out of which the ova will grow)
start to divide by mitosis (DNA gets duplicated) over
and over again.
2. These cells will grow to larger cells, then they are
called primary oocytes.
3. The primary oocytes start to divide by meiosis, the
process is arrested (stopped) for some years though.
This division is called Meiosis I.
4. Some other cells within the ovaries undergo cell
division too. They cover the primary oocytes with a cell
layer called the follicle.
The (still dividing) primary oocytes and their follicle are called
primary follicles. At birth, the girl has around 400 000 primary
follicles in its ovaries. They won’t change/develop until
puberty.
5. At the start of each menstrual cycle, some primary
oocytes finally divide. The two cells formed aren’t even close to being equal in size. The smaller one is called
the first polar body and acts as a reservoir of the surplus chromosomes. The big cell is called secondary
oocyte. Usually only one becomes a mature follicle, containing a secondary oocyte.
6. The follicle cells around the (now) secondary oocyte start to develop and form a double-layered follicle.
There’s the secondary oocyte. Then there’s the first layer of the follicle surrounding the oocyte. Then
there’s a fluid and then there’s the second layer of the follicle. This is called a Graafian follicle.
7. At ovulation the secondary oocyte and the inner follicle layer will be released. If it don’t get fertilized, the
cell will remain an secondary oocyte until it dies. If it does get fertilized it will be doing meiosis II.
Meiosis
Mitosis
Follicle
Primary follicle
oogonia cells
oocyte
Primary oocyte
Secondary oocyte
First polar body
Cell division, DNA isn’t duplicated
Cell division, DNA is duplicated
Cell layer around the egg cell
Egg cell and follicle
Cells out of which the ova will grow
female reproductive cell prior to fertilization
Oocyte before meiosis I
Oocyte after meiosis I
The void cell created during meiosis I
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Spermatogenesis
Spermatogenesis is the production of sperm. It happens in the
testes, which are composed of a mass of narrow tubes, called
seminiferous tubules. The seminiferous tubules are made out
of cells – the outer layer of these cells is called germinal
epithelium. Spermatozoa is the actual word for sperm, this
word is almost always abbreviated as sperm though.
1. Outside of the tubules are germ cells called
spermatogonium.
2. They all grow, duplicate the DNA and then divide
through mitosis. The same thing happens again
and again. They divide through mitosis to increase
their number. A man can produce one million
sperms per day.
3. At some point, they divide through meiosis: They
first had 23 pairs of chromosomes, now they have
23 single chromosomes. This called a haploid
number of chromosomes.
4. Out of each of these divisions, 4 mature sperm
heads are created
5. They will stay in the inside of the testes for some time until they have developed other features:
flagellum (tail) for movement and an acrosome which contains the enzymes needed for fertilization.
6. The developing sperms need nutrients for their development. They therefore attach to a Sertoli cell until
they are fully developed.
Seminiferous
tubules
Germinal
epithelium
Spermatozoa
Haploid
Acrosome
Sertoli cell
Tubules in the testes in which sperm is produced.
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Outermost layer of the seminiferous tubules
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= sperm
23 single chromosomes instead of 23 pairs of chromosomes – half the number of
chromosomes
contains the enzymes needed for fertilization
Provides sperm with nutrients for development
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Processesofspermatogenesisandoogenesisresultin
differentnumbersofgameteswithdifferentamountof
cytoplasm.
The ovum (secondary oocyte) is the largest cell in most
animals. It contains a lot of cytoplasm and nutrients
needed to provide the future baby with nutrients.
Mitosis replaces germinal cells daily
The two divisions of meiosis result in 4 haploid sperms.
The sperm in contrast are very small cells, containing a
flagellum and mitochondria for ATP production and no
cytoplasm. Both of the cells are perfectly suited for their
job.
Mitosis replaces germinal cells only when the girl’s an
unborn.
The two divisions of meiosis result in 1 ovum.
Theaverage38-weekpregnancyinhumanscanbe
positionedonagraphshowingthecorrelationbetween
animalsizeandthedevelopmentoftheyoungatbirthfor
otheranimals
Mammals either give birth to babies which aren’t far developed, have their eyes closed, no hair, can’t defend
themselves or can’t look for food on their own.
Or they give birth to babies which are further developed and have hair, can look for food on their own and even can
defend themselves a bit against predators.
Mostly big mammals use the second strategy. It is correlated with long times of pregnancy. The longer the women is
pregnant, the more developed the baby will be at birth. By comparing the duration of pregnancies of different
mammals, one can tell how far developed the baby will be at birth.
Annotationofdiagramsofseminiferoustubuleandovaryto
showthestagesofgametogenesis
Annotationofamaturespermandeggtoindicatefunctions
Sperm
Acrosome: Release enzymes when binding with
follicle so the sperm can get through the follicle.
Haploid nucleus: Contains the 23 single
chromosomes. Tell the sperm what to do (swim etc.)
Mitochondria: Produced ATP such that the sperm
is able to swim.
Flagellum: Used to swim.
Ovum
Follicle cells:
Protect the secondary oocyte.
Zona pellucida:
Makes sperm’s acrosome release digestive enzymes which enable them to pull
though the layers. After the first sperm entered, the zona pellucida hardens, trapping
any other sperms which couldn’t get inside. New coming sperms can’t attach to the
zona pellucida anymore.
Cytoplasm:
Containing yolk and all organelles typical for body cells
Plasma membrane:
Pulls sperm inside and makes that no other sperm can enter (change of
characteristics of egg).
Numerous cortical granules: Tell de zona pellucida to harden and keep other sperm outside.
Haploid nucleus:
Contain the 23 chromosomes