INTERPHASE In nucleus 2 identical arms constricted area

INTERPHASE In nucleus

_________ 2 identical arms _________constricted area holds chromatids together

MITOSIS Begin with a Diploid Cell 2 N = 4

MITOSIS Chromosomes are in a single file line

MITOSIS Centromere divides Sister chromatids move apart

End with two Diploid Cells that are identical MITOSIS

INTERPHASE In nucleus

MEIOSIS

MEIOSIS Homologous chromosomes form tetrads at the equator = pair of homologous chromosomes

Homologous chromosomes move AWAY to the poles MEIOSIS

2 cells so far MEIOSIS

Meiosis II Interkinesis • Nuclear membrane forms • NO replication of chromosomes

MEIOSIS

Chromosomes align at the equator MEIOSIS NOW … single file line

Centromeres divide MEIOSIS

End with 4 Haploid Cells All are different n=2 MEIOSIS

Meiosis – one more time Meiosis is a two-part cell division process….

Meiosis II – one more time … which results in 4 gametes with one half the number of chromosomes of the parent cell.

Crossing Over • To make things more interesting, crossing over can occur. • During metaphase I, the homologous chromosomes line up together and form tetrads. Remember? ?

Crossing Over • Crossing over takes place when two chromosomes, break and then reconnect but to the different end piece. • Crossing over increases the number of variations that can exist in offspring.

Crossing Over • Which of the following did crossing over ONLY take place?

Comparison of Divisions Mitosis Number of divisions Number of daughter cells Genetically identical? 1 2 2 4 Yes No Chromosome # Same as parent Role Meiosis Growth and Repair Half of parent Sexual reproduction

Homologous Chromosomes • The two chromosomes of each pair in a diploid cell are called homologous chromosomes.

Homologous Chromosomes Match up the homologous chromosomes

Memory Phrase Meosis made ME-osis Mitosis made my-TOES-es