Gametogenesis involves the formation of
male and female reproductive cells, i. e., sperms and ova under the influence
of hormones. Spermatogenesis is the process of formation of sperms and that of
ova is called oogenesis.
Mammalian sperm vs Mammalian Ovum
The sperms are microscopic and motile
cells. A mature spermatozoan is about 60 um long, flagellated, motile cell. It
consists of head, neck, middle piece and a long narrow tail. The shape of
spematozoan helps to surge forward
relentlessly in the vast female genital tract until it reaches its target, the ovum, situated at the outer end of
fallotubian tube. Sperms remain alive
and retain their ability to fertilize the ovum from 24 to 48 hours after being entered
in the female reproductive tract.
The ovum in humans is alecithal,
i.e. it is almost devoid of yolk and has
bulky cytoplasm and a centrally located
nucleus. It measures approximately 100 μm
in diameter and remains surrounded by a secreted transparent , non cellular layer
called zona pellucida. An in vestment of radially elongated follicle cells is
present outside this layer which is known as corona radiate. Between the cell membrane
or vitelline membrane and the zona pellucida, a distinct space , said to be
perivitelline space, is present.
Mammalian Sperms
1. Sperm is flagellated and motile.
2. A sperm is formed of four parts: Head, neck, middle piece and
tail.
3. Small amount of cytoplasm is present
4. Nucleus condensed with no nucleoplasm.
5. Centrioles is present.
6. Mitochondrion is compactly arranged and form a spiral called
nebenkern.
7. Surrounded by only plasma membrane.
Mammalian ovum
1. Ovum is spherical and non motile.
2. Ovum is alecithal and has an excentric nucleus.
3. Large amount of cytoplasm is present.
4. Nucleus is bloated with nucleoplasm and is called germinal
vesicle.
5. Centrioles is absent.
6. Mitochondria scattered in the cytoplasm.
7.Surrounded by a number of egg envelopes.
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