Meiosis-Meiosis-

• Process that Process that produces haploid produces haploid gametes from gametes from diploid cellsdiploid cells

• Reduces the Reduces the number of number of chromosomes to chromosomes to halfhalf

GametesGametes

• Reproductive cells Reproductive cells • Male- sperm cellsMale- sperm cells• Female- egg cells Female- egg cells

(ova)(ova)

Diploid-Diploid-

• The total number of The total number of chromosomes (2N)chromosomes (2N)

• All non-All non-reproductive cells- reproductive cells-

• Both sets of Both sets of homologous homologous chromosomeschromosomes

• Ex. drosophila Ex. drosophila (fruit fly) = 8(fruit fly) = 8

• Ex. human = 46Ex. human = 46

Haploid (monoploid)-Haploid (monoploid)-

• ½ the total number ½ the total number of chromosomes of chromosomes (1N)(1N)

• Only gametes Only gametes (reproductive cells)(reproductive cells)

• Single set of Single set of chromosomeschromosomes

• Ex. drosophila = 4Ex. drosophila = 4• Ex. human = 23Ex. human = 23

Two division processTwo division process

• Meiosis I Meiosis I – Stages of 1Stages of 1stst cell cell

divisiondivision

• Meiosis IIMeiosis II– Stages of 2Stages of 2ndnd cell cell

divisiondivision

• pp 162-163pp 162-163

Two division processTwo division process

• Meiosis IMeiosis I• Synapsis- the Synapsis- the

pairing of pairing of homologous homologous chromosomes. chromosomes. (does not occur in (does not occur in mitosis)mitosis)

• RandomRandom

Two division processTwo division process

• Meiosis IMeiosis I• Tetrad- each pair of Tetrad- each pair of

homologous homologous chromosomes (4 chromosomes (4 replicated replicated chromatids) (page chromatids) (page 162)162)

• Crossing Over- when Crossing Over- when chromosomes that chromosomes that make up a tetrad make up a tetrad exchange parts of exchange parts of their chromatidstheir chromatids

Two division processTwo division process

• Meiosis IIMeiosis II• Basically just like Basically just like

mitosismitosis• 2 haploid cells will 2 haploid cells will

result in 4 haploid result in 4 haploid cellscells

Meiosis in MalesMeiosis in Males

• Spermatogenesis-Spermatogenesis-• One diploid cell One diploid cell

results in the results in the formation of 4 formation of 4 sperm cellssperm cells

• p 164p 164

Meiosis in FemalesMeiosis in Females

• OogenesisOogenesis• One diploid cell One diploid cell

results in the results in the formation of 1 formation of 1 egg cell and 3 egg cell and 3 polar bodiespolar bodies

• p 164p 164

Mitosis vs MeiosisMitosis vs Meiosis

Characteristic/EventCharacteristic/Event MitosisMitosis MeiosisMeiosis

Number of daughter Number of daughter cellscells

Daughter cells Daughter cells identical or different identical or different than parentthan parent

Chromosome number Chromosome number for daughter cells for daughter cells (2n/1n)(2n/1n)

Number of divisionsNumber of divisions

Type of cell producedType of cell produced

Video- “The Meiosis Square Video- “The Meiosis Square Dance”Dance”

• Introduces the process of meiosis by-Introduces the process of meiosis by-– Presenting the chromosomes as Presenting the chromosomes as

characters at a square dance held characters at a square dance held inside a fruit fly. inside a fruit fly.

– Dino and Dina Chromosome coil up, Dino and Dina Chromosome coil up, duplicate, cross over, and separate as duplicate, cross over, and separate as they dance their way through they dance their way through interphase, prophase, metaphase, interphase, prophase, metaphase, anaphase, telophase, and cytokinesis. anaphase, telophase, and cytokinesis.

All Images- Clip ArtAll Images- Clip Art