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Meiosis
Spermatogenesis & Oogenesis
Importance of Meiosis
 Cell division that only occurs for sexual
reproduction.
 Creates gametes like sperm and egg cells in
animals, or spores in plants, algae, and fungi.
(our focus is animals)
 Begins with one diploid cell that contains two
sets of chromosomes.
 One from the organisms mother and one from
the organisms father.
 Produces four haploid cells containing one copy
of each chromosome.
 Fun fact: Mitosis cannot produce haploid cells.
Importance of Meiosis
Importance of Meiosis
 Diploid cells – having two of each chromosome.
Human cells have 23 pairs of chromosomes.
 The diploid number of chromosomes is
represented by 2n.
 “n” = the number of different pairs.
 Humans -> 2n = 46
Importance of Meiosis
 Each haploid cell contains the number of
chromosomes needed to be passed onto the
next generation.
 Without meiosis the life cycle could not
continue.
 Provides variation among offspring.
 A process that reshuffles chromosomes to
create a variations.
Importance of Variation
 It provides a better chance for survival.
-individuals will have different traits.
-prepared for environmental changes.
 The number of individuals with undesirable
combinations of genes is decreased.
-Genetic traits allow organisms to adapt to a
certain environment.
Interphase I
 Cell undergoes regular metabolic processes
and protein synthesis.
 Organelles double in number.
 DNA replicates and becomes uncoiled.
 2n genetic compliment
Prophase I
 The chromosomes condense and migrate
towards the nuclear envelope.
 Each chromosome is made up to two
identical chromatids, known as sister
chromatids.
 Centrioles migrate to opposite poles.
 Formation of spindle fibres.
 Pairing of homologous chromosomes
(crossing over may occur).
 Nuclear envelop & nucleoli dissolves
 2n x 2 genetic compliment
Metaphase I
 Chromosomes move to equatorial
plate.
 2nx 2 genetic compliment
Anaphase I
 Chromosomes migrate to poles.
 Sister chromatids are not
separated.
 2n x 2 genetic compliment.
Telophase I
 Cytokinesis; division of cellular
contents.
 Nuclear envelop temporarily
forms.
 Each cell has 2n genetic
compliment.
Prophase II
 Spindle reforms and connects
chromatids.
 Nuclear envelop dissolves.
 Each cell has 2n genetic
compliment.
Metaphase II
 Chromosomes brought to
equatorial plate.
 2n genetic compliment.
Anaphase II
 Chromatids separate and move to
opposite poles.
 2n genetic compliment.
Telophase II
 Nuclear envelop forms around
haploid nuclei.
 Each cell is haploid:
(n genetic compliment)
-Short video on Meiosis:
Definitions:
 Cytokinesis: the division of the cytoplasm.
 Parent cell: cell that divides to form new
daughter cells.
 Daughter cells: cells that arise as a result of
cell division.
 Homologous Pair: two chromosomes that have
information for the same trait.
 Homologue: one of the two chromosomes that
make up a homologous pair.
 Oogenesis: Formation of ova.
 Oogonia: stem cell for developing ova.
Definitions: (continued)
 Primary Oocyte: daughter cell of oogonia after
meiosis.
 Primary Spermatocyte: daughter cell of
spermatogonia.
 Secondary Oocyte: daughter cell of primary
oocyte.
 Secondary Spermatocyte: daughter cell of
primary spermatocyte.
 Sperm: male sex cell.
 Spermatogenesis: process of producing
spermatocytes.
 Spermatogonia: parent cell of sperm.
Male and Female Meiosis
 Spermatogenesis: process of
producing spermatocytes.
 Oogenesis: formation of an ova.
Fig. 7-16
(In Biology, Living Systems text)
Bibliography

Oram, Raymond F. (1994). Biology, living systems. Glencoe/McGraw-Hill. Westerville. 182-189.