Transcript Gametogenesis - NCEA Level 2 Biology

Gametogenesis
To describe the process by which
gametes are produced.
What is Gametogenesis?
 This is the process by which sex cells are
made.
 Meiosis is the production of sex cells.
 Meiosis is different in males and females.
Spermatogenesis
 This is the formation of Sperm Cells.
 In males, each cell formed becomes a
sperm cell.
 This happens by the process of meiosis
in an uninterrupted sequence.
 The process occurs in adult males,
producing as many as 250 – 400 million
sperm cells in each ejaculation (± 5ml).
Spermatogenesis
OOgenesis
 This is the formation of ova or egg cells.
 Oogenesis differs from spermatogenesis
in a number of ways.
 During the first meiotic division, cytokinesis is
uneven, one cell takes all the cytoplasm.
 This large cell goes on to form the egg, the
smaller cell forms polar bodies, which
disintegrate.
OOgenesis Cont
 At birth the ovary has all the cells it will ever
have to develop into eggs.
 The formation of the eggs involves long
“resting periods”.
 Between birth and puberty, the egg cells
enlarge and the follicles around them grow.
The primary egg cells replicate their DNA,
they enter Prophase 1 but do not change
again until reactivated by hormones at
puberty.
OOgenesis Cont
 After puberty, an egg cell stimulated by
hormones, periodically completes meiosis 1
and then stops.
 This is the form in which it is released in the
menstrual cycle.
 Penetration of the sperm cell triggers the
second meiotic division in humans.
OOgenesis
Summary