Eukaryotic Cell Cycle

• Cell cycle: repeating sequence of cellular growth and division during the life of the cell– Interphase– Mitosis– Cytokinesis

Interphase• Cell is growing and

preparing to divide• G1 (First Gap) phase

– Cell grows rapidly• S (synthesis) phase

– Cell’s DNA is copied– Each chromosome now has

2 identical chromatids• G2 (Second Gap) phase

– Cell continues to grow and prepare for division

– Microtubules form

Mitosis

• Process of dividing the nucleus into two daughter nuclei– Prophase– Metaphase– Anaphase– Telophase

Prophase

• Chromosomes condense

• Nuclear membrane dissolves

• Centrosomes (centrioles) move to opposite poles and spindle forms

Metaphase

• Condensed chromosomes line up at cell’s equator

• Spindle fibers link the individual chromatids to opposite poles

Anaphase

• Spindle fibers shorten• Chromatids pulled to

opposite poles of cell giving each pole identical sets of chromosomes

Telophase

• New nuclear envelope forms at each pole

• Spindle dissolves• Chromosomes uncoil

(chromatin)

Cytokinesis

• Cell membrane grows into the center of the cell and divides it into two daughter cells of equal size– each daughter cell has

about half of the parent’s cytoplasm and organelles

Cytokinesis• Animal cells: cell is pinched in half by a belt of protein threads• Plant cells: vesicles holding cell wall material line up in the middle to fuse

into a cell plate which separates the new cells

End Results

• Two identical cells• New daughter cells half

the size of the parent cell

• Each cell enters G1

Types of Cell Reproduction

• Asexual: single parent passes a complete copy of its genetic information to each of its offspring– Offspring look identical

to parent (MITOSIS)

Types of Cell Reproduction

• Sexual: two parents give genetic material to produce offspring that are genetically different from their parents (MEIOSIS)

What are some advantages of sexual reproduction?

Meiosis

• Process in which a cell is divided and produces gametes (sperm or eggs): 2 rounds of division (P-I, M-I, A-I, T-I, then P-II, M-II, A-II, and T-II)– end with 4 haploid cells

Homologous Chromosomes

• Chromosomes that are similar in size, shape, and in kinds of genes that they contain

• Each chromosome in a homologous pair comes from one of the two parents

• Each species has a different number

Chromosome Number

• Gametes are haploid• Somatic cells are diploid

Example: Horse skin cell = 64

chromosomes = diploid (2n)

Horse egg cell = 32 chromosomes = haploid (n)

Chromosome Number

• Species: a population of organisms that are able to breed and produce fertile offspring– Same number of

chromosomes

Crossing Over

• Prophase I• Chromatids exchange

genetic material between homologous chromosomes during meiosis

What is the advantage of crossing over?

Meiosis

Two divisions to get 4 haploid cells

Comparing Mitosis and Meiosis

Process Location # of Cells Produced

Haploid/Diploid

Type of Cell Produced

Importance of Process

Mitosis Somatic Cells(Ex: skin cells)

2 diploid Identical diploid cells

Healing/repair, maintenance/replacement of old cells, and growth

Meiosis Sex Cells (gametes)

4 haploid Different haploid cells

Reproductive purposes; increases genetic diversity amongst organisms

Comparing Mitosis and Meiosis