Gamete Production

MeiosisMeiosisSimilar in many ways to mitosisSimilar in many ways to mitosisSeveral differences howeverSeveral differences however

Involves 2 cell divisionsInvolves 2 cell divisionsResults in 4 cells with 1/2 the normal genetic information.Results in 4 cells with 1/2 the normal genetic information.

Vocabulary:Vocabulary:Diploid (2N)Diploid (2N) - Normal amount of genetic material - Normal amount of genetic materialHaploid (N)Haploid (N) - 1/2 the genetic material. - 1/2 the genetic material.

Meiosis results in the formation of haploid cells.Meiosis results in the formation of haploid cells.In Humans, these are the In Humans, these are the OvaOva (egg) and (egg) and spermsperm..Ova are produced in the Ova are produced in the ovariesovaries in females in females

Process is called Process is called oogenesisoogenesisSperm are produced in the Sperm are produced in the testestestes of males. of males.

Process is called Process is called spermatogenesisspermatogenesisMeiosis occurs in 2 phases: Meiosis occurs in 2 phases: Meiosis 1Meiosis 1 & & Meiosis 2Meiosis 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-OVERProphase 1 – CROSSING-OVERSegments of Segments of

homologous homologous chromosomes break chromosomes break and reform at similar and reform at similar locations.locations.

Results in new Results in new genetic combinations genetic combinations of offspring.of offspring.

This is the main This is the main advantage of sexual advantage of sexual reproductionreproduction

Anaphase 1Anaphase 1 During anaphase 1, each homologous chromosome is pulled to opposite During anaphase 1, each homologous chromosome is pulled to opposite

sides of the cell. Unlike mitosis, sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT THE CENTROMERES DO NOT BREAKBREAK..

Meiosis II – Follow the same steps as MITOSISMeiosis II – Follow the same steps as MITOSIS

DNA DNA does notdoes not double doubleChromosomes randomly line-up along middle like regular Chromosomes randomly line-up along middle like regular

mitosis.mitosis.During anaphase 2, During anaphase 2, CENTROMERES BREAKCENTROMERES BREAK and and

each chromosome is pulled to opposite sides of the cell.each chromosome is pulled to opposite sides of the cell.Nuclei reform and cytokenesis occursNuclei reform and cytokenesis occurs

Meiosis Prophase I Metaphase I Anaphase I Telophase I

Overview of MeiosisOverview of Meiosis

MeiosisB-4.5 Summarize the characteristics of

the phases of meiosis I and II.

Taxonomy Level: 2.4-B Understand Conceptual Knowledge

Key ConceptsDaughter cells: diploid; haploid, gamete,

zygoteMeiosis I: interphase, prophase I, tetrad,

crossing over; metaphase I; anaphase I; telophase I,

cytokinesisMeiosis II: prophase II, metaphase II,

anaphase II, telophase II

Meiosismeiosis is important to sexual reproductionmitosis 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 withduplicated 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 chromosome-pair at the first division of meiosis.

Meiosis I