Cell division

Goals

1. To understand the problems that cell division poses for the cell, and the solutions it has arrived at for these problems

2. To understand sexual life cycles and the necessity of meiosis

3. To understand how meiotic division occurs, and to be able to compare and contrast it with mitosis

4. To understand the consequences of meiosis for the genes carried on the chromosomes

Outline

1. The reproduction of cells:

• must make duplicates of everything essential
• must get it into 2 different places
• must split into two daughter cells

2. Prokaryotic cell division: binary fission

3. Eukaryotic cell division: mitosis and cytokinesis

6 easy steps:

1. replicate DNA
2. packaging -- condense chromosomes into heterochromatin
3. assemble mitotic spindle
4. move chromosomes into place (using the mitotic spindle)
5. split and move chromosomes to cell poles
6. divide up the cytoplasm: cytokinesis

...or five phases --- IPMAT

4. Life cycles

the diploid state:

pairs of homologous chromosomes

genes at loci on chromatids

genes on homologous pairs may be different alleles

sexual reproduction involves switching between haploid and diploid -- allows genetic variation among offspring

meiosis and fertilization are the processes by which do this

5. Meiosis

Meiosis I

• homologous pairs of chromosomes pair up (synapse) to form tetrads
• tetrads may form chiasmata and crossing over may occur
• homologous chromosomes split and go to either cell pole to form haploid cells

Meiosis II

• like mitosis but haploid

6. Consequences of meiosis and sexual reproduction

Allows genetic variation among offspring through:

1. Independent assortment of pairs of homologous chromosomes
2. crossing over
3. random fertilization

Vocabulary

click here to go to Cell division vocabulary