Gametogenesis

2. Gametogenesis is aprocess
by
which diploid or haploid
cells undergo cell
division and differentiation
to form mature
haploid gametes.

3. occurs
by meiotic division
of
diploid gametocytes
into various
gametes, or
by mitotic division
of haploid
gametogenous cells.
The existence of a
multicellular, haploi
d phasein the life
cycle between
meiosis and
gametogenesis is also
referred to
asalternation of
generations.

4. the process of gametes
formation
It occurs in the gonads
(ovary or testis)

6. Gonial cells arethe designation givento
germ cells before they enter meiosis.
•replicate mitotically.
•genetically identical to the original zygote.
•When they begin meiosis, they are
called spermatocytes and oöcytes.

9. Spermatogenesis
isthe processof formation of the malegerm
cells(sperm formation).
It occursin the seminiferoustubulesof the
testis.
It isthread-like in shape.

11. Spermatogenesis occursfrom puberty to old
age, producingimmensenumbersof spermatozoaat
anaverage rate of 1.5millionspermatozoaper
minute.
The spermwill mature in the
epidiymis, nourishedby sertoli cells for upto 10
weeks.
Humansaged13-90canmake1billion sperm a
day.

12. The sertoli cellsaresupportingcellsthat haveseveral
functions.
They form the blood-testesbarrier: nutrients, andcirculating
substancesdonot directly reachthe germcells
The sertoli cellsdetermine which substancesreachthe
germ cells
 The spermatogoniaareoutsidethe blood-testis barrier.
They alsoproduceantigen-binding proteins, which are
necessaryfor spermiogenesis(morphologicaldevelopment
ofspermatids to spermatozoa).

14. Spermatogenesisisthe processbywhich maleprimary sperm
cells undergomeiosis, andproduceanumberof cells
termedspermatogonia,from which the primary spermatocytes are
derived.
Eachprimary spermatocytedividesinto two secondary
spermatocytes,andeachsecondaryspermatocyteinto
two spermatids oryoung spermatozoa.
Thesedevelopinto mature spermatozoa,alsoknown
asspermcells.
The primary spermatocytegivesriseto two cells,the secondary
spermatocytes,andthe two secondaryspermatocytesbytheir
subdivisionproducefour spermatozoa.

15. It isanintermediary malegametogonium
(a kind of germ cell).
Diploid in number:44 autosomesand2sex cells
It isvery small andunderthe processof
development.
Undergoing G1-S.

16. diploid in number:
44 autosomesand2sex cells
Increasesin size
Undergoing G2.

17. Haploid in number:22autosomes
(double stranded) and1sexcelleach.
Can seethe cleavagefurrow
UndergoingMeiosis I (ReductionDivision)
Chromosomesarereducedinto half number.

18. Haploid in number:
22 (singlestranded) autosomes and
1 sex cell.
Undergoing Meiosis II
(Equational Division)

19. It isamotile spermcell, or moving form
of the haploid cell that isthe male gamete.
It joins anovumto form a zygote.
Matured SpermCell arereadyto
fertilized the egg.

21. Oogenesis isthe processof formation
of the female germcells(egg formation).
It happensin theOvary.
It isSphericalin shape.

22. Oogenesis beginsin early foetal life.
All oocytesformed in femalesareproducedduring foetal life.
Many of them degeneratewith time andat birth the ovaries
contain about2million oocytes.
All the oocytesgointo meiotic arrest whenthey reachthe first
meiotic division during foetal life.
The primary oocytesremain in the prophaseof the first meiotic
division until the time of puberty, whenthey aregradually
releasedto completemeiosisat regular intervals known asthe
ovarian cycle.
On the averageonly oneoocytematuresduring each
cycle, which occursat approximately monthly intervals, sothat
the total amountof oocytesto beovulatedisabout500oocytesin a
lifetime.

24. Oogonium/Oogonia