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Gamete Formation BIO 101

Gamete formation involves the production of sperm and eggs through spermatogenesis and oogenesis respectively. Both processes involve mitosis followed by two rounds of meiosis to produce haploid gametes from diploid germ cells. In spermatogenesis, spermatogonia undergo mitosis and two rounds of meiosis to form mature sperm. In oogenesis, oogonia undergo mitosis while oocytes arrest during the first meiotic division, and only complete meiosis upon fertilization. This ensures the production of haploid gametes that can fuse during fertilization.

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102 views3 pages

Gamete Formation BIO 101

Gamete formation involves the production of sperm and eggs through spermatogenesis and oogenesis respectively. Both processes involve mitosis followed by two rounds of meiosis to produce haploid gametes from diploid germ cells. In spermatogenesis, spermatogonia undergo mitosis and two rounds of meiosis to form mature sperm. In oogenesis, oogonia undergo mitosis while oocytes arrest during the first meiotic division, and only complete meiosis upon fertilization. This ensures the production of haploid gametes that can fuse during fertilization.

Uploaded by

Esther Ekeng
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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BIO 101

Gamete Formation
Introduction
Sexual reproduction involves the fusion of special cells, reproductive cells. These
cells contain half the number of chromosomes (units of heredity) as a normal cell in
the body (somatic cell), so that when two of the reproductive cells fuse, a variety of
members of the species will arise. This helps the chances of progeny’s survival.
Gamete formation is the formation of sex cells i.e reproductive cells in an organism.

Male gametes are called sperm and female gametes are called ova or egg cells. The
formation of sperm is called spermatogenesis and the formation of egg cells is
called oogenesis.
Meiosis (reduction division) is principal in both spermatogenesis and oogenesis. It
occurs in three major steps:
1. mitosis
2. meiosis I
3. meiosis II

Spermatogenesis

Part one: The spermatogonium, which is the origin cell in spermatogenesis, divides
by mitosis. The spermatogonium contains 2n chromosomes, where n is the haploid
number of chromosomes (i.e half the number of chromosomes in a somatic cell).
The products of this division are two primary spermatocytes with 2n chromosomes.

Part two: This is meiosis I. The primary spermatocytes divide during meiosis I,
forming two haploid secondary spermatocytes.

Part three: Secondary spermatocytes divide by meiosis II into spermatids


(immature sperm cells) connected by cytoplasmic bridges. Since much of the
information needed for the maturation of sperm is located on the X chromosomes,
the closeness provided by the cytoplasms helps share that information with sperm
with Y chromosomes.
BIO 101
Part four: fully developed, haploid, male sex cells and mature spermatozoa separate.
This happens at sexual maturation. In males, many sperm cells are produced to
increase chances of fertilization — around several million.

Diagrammatic representation of Spermatogenesis

Oogenesis
It starts with the oogonia, which are the diploid cells from which all oocytes
(immature ova) are formed. The formation of oogonia is technically not part of
gamete formation since they are all present at birth.

Part one: after a female is born, oogonia undergo mitosis to form the diploid
primary oocytes. This is called oocytogenesis.

Part two: The secondary oocytes are formed, through meiosis of the primary
oocytes. The meiosis stops in prophase I and only continues when the female goes
BIO 101
through their fertile period. Only some cells move forward for this, ranging from a
singular cell, to hundreds.

Part three: The oocytes that continue form one secondary oocyte and one polar
body. A polar body is a non-viable haploid cell with little cytoplasm. The Bible
secondary oocyte stops at metaphase II of meiosis II until fertilization occurs.

Part four: upon fertilization, the oocyte complètes meiosis to form an ootid (a
fertilized egg cell) and another polar body.

Diagrammatic representation of Oogenesis

References
https://youtu.be/-RXCTbFp1ME
https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/43%3
A_Animal_Reproduction_and_Development/43.3%3A_Human_Reproductive_Anatomy_and_Gametogenesis/43.3C%3A__
Gametogenesis_(Spermatogenesis_and_Oogenesis)
https://youtu.be/lH9loPdk_nQm

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