Gamete Production
Meiosis
 Similar in many ways to mitosis
 Several differences however
 Involves 2 cell divisions
 Results in 4 cells with 1/2 the normal genetic information.
 Vocabulary:
 Diploid (2N) - Normal amount of genetic material
 Haploid (N) - 1/2 the genetic material.
 Meiosis results in the formation of haploid cells.
 In Humans, these are the Ova (egg) and sperm.
 Ova are produced in the ovaries in females
 Process is called oogenesis
 Sperm are produced in the testes of males.
 Process is called spermatogenesis
 Meiosis occurs in 2 phases: Meiosis 1 & Meiosis 2
Spermatogenesis & Oogenesis
REMEMBER:
I P1 M1 A1 T1 P2 M2 A2 T2 C
MEIOSIS AND MITOSIS ARE THE
SAME EXCEPT FOR:
 PROPHASE I
 ANAPHASE I
Prophase 1 – CROSSING-OVER
 Segments of
homologous
chromosomes break
and reform at similar
locations.
 Results in new
genetic combinations
of offspring.
 This is the main
advantage of sexual
reproduction
Anaphase 1
 During anaphase 1, each homologous chromosome is pulled to opposite
sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT
BREAK.
Meiosis II – Follow the same steps as MITOSIS
 DNA does not double
 Chromosomes randomly line-up along middle like regular
mitosis.
 During anaphase 2, CENTROMERES BREAK and each
chromosome is pulled to opposite sides of the cell.
 Nuclei reform and cytokenesis occurs
Meiosis
Prophase I
Metaphase I
Anaphase I
Telophase I
Overview of Meiosis
Meiosis
 B-4.5 Summarize the characteristics of the phases
of meiosis I and II.
 Taxonomy Level: 2.4-B Understand Conceptual
Knowledge
Key Concepts
 Daughter cells: diploid; haploid, gamete, zygote
 Meiosis I: interphase, prophase I, tetrad, crossing over;
metaphase I; anaphase I; telophase I,
 cytokinesis
 Meiosis II: prophase II, metaphase II, anaphase II,
telophase II
Meiosis
 meiosis is important to sexual reproduction
 mitosis is important to asexual reproduction
 In order for the offspring produced from sexual
reproduction to have cells that are diploid (containing
two sets of chromosomes, one set from each parent),
the egg and sperm cells must be haploid (contain only
one of each type of chromosome).
 The division resulting in a reduction in chromosome
number is called meiosis.
Meiosis occurs in two steps:
 Meiosis I, in which the chromosome pairs replicate, results in
two haploid daughter cells with
 duplicated chromosomes different from the sets in the original
diploid cell.
 Meiosis II, in which the haploid daughter cells from Meiosis I
divide, results in four haploid daughter cells called gametes, or
sex cells (eggs and sperm), with undoubled chromosomes.
 Tetrad
 The four haploid cells formed at the end of meiosis. The term was
formerly used for the four chromatids making up a chromosomepair at the first division of meiosis.
Meiosis I