Cell Reproduction

Chromosome Structure Review Except for the gametes, humans have 46 chromosomes (23 pairs) in the nucleus of every cell. Chromosomes are long strands of DNA (genetic code). When chromosomes are uncoiled, they are called chromatin. When chromosomes are coiled, they look like a “x”.

Chromosome Structure Review Chromatids- Each half of a chromosome Each chromatid is a double helix (twisted ladder) Centromere- holds 2 chromatids together

Cells with different numbers of chromosomes Diploid (somatic cell) – A cell consisting of homologous chromosomes . In humans, this cell has 46 chromosomes. One chromosome of a pair came from the mother and one from the father. All cells in the human body are diploid except sex cells. Haploid (gamete) – A cell that does not contain chromosome pairs. The sperm and egg are haploid and, in humans, have 23 chromosomes.

Chromosome Shorthand X XX n = # of unique chromosomes (haploid) 2n = # of chromosomes in pairs (diploid) n=4 Haploid cell 2n=8 Diploid cell X XX X XX xx x Homologous Pair xx x

Cell Cycle- Series of events for cells   Interphase is the time between cell division. This is when the cell grows and replication occurs (chromatids are copied). During interphase, DNA is uncoiled (chromatin). Mitosis/Meiosis is the division of the cell’s nucleus (chromosomes). Cytokinesis is division of the cell’s cytoplasm and membrane. This is when the cell physically splits in half.   Cytokinesis Interphase Mitosis or Meiosis

MITOSIS Mitosis results in new cells with genetic material identical to that of the original cell. This process is the reason for human growth. Mitosis occurs in all cells of the body except the sex cells (egg and sperm cells). Sex cells undergo a different process called meiosis. Mitosis has 4 phases: Prophase, Metaphase, Anaphase and Telophase.

PROPHASE DNA supercoils (goes from chromatin to chromosomes) Nuclear membrane breaks down Nucleolus breaks down Mitotic spindle forms from the centrosomes (containing 2 centrioles)

METAPHASE Chromosomes line up in single file at the center of the cell. The chromosomes (at the centromere) are held in place by the mitotic spindle.

ANAPHASE The chromatids of each chromosome separate and move toward opposite poles of the cell. The spindle pulls the chromatids apart at their centromere.

TELOPHASE (opposite of Prophase) Mitotic spindle breaks down Chromosomes uncoil (become chromatin) Nuclear envelopes reform Nucleolus reappears within each envelope

CYTOKINESIS Cytokinesis occurs differently in animal and plant cells. In animal cells, the cell membrane pinches in until it eventually splits the cell into two. This pinching in is called a cleavage furrow.

CYTOKINESIS In plant cells, cytokinesis occurs when a cell plate forms and splits the cell into two. The cell plate starts to form in the center and works its way outward until it reaches the cell wall.

Mitosis and Cytokiinesis Practice Each student kit needs: one 8 foot orange string cut in ½ One 5 foot black string cut in ½ 2 clear spoon and fork 2 white spoon and fork 2 pom-poms 2 paper clips 8 coffee stirrers

What is the cell cycle phase? (IPMATC)

What is the cell cycle phase? (IPMATC)

What is the cell cycle phase? (IPMATC)

What is the cell cycle phase? (IPMATC)

What is the cell cycle phase? (IPMATC)

What is the cell cycle phase? (IPMATC)

Meiosis A type of cell division in which the chromosome # is reduced by half to produce haploid cells. This produces gametes (sex cells). Meiosis has the same phases as mitosis; however, it goes through 2 rounds of these phases. The phases of meiosis are Prophase I/II, Metaphase I/II, Anaphase I/II and Telophase I/II.

PROPHASE I Nuclear membrane breaks down Nucleolus breaks down Mitotic spindle forms from the centrosomes Chromatin coils to become chromosomes Homologous chromosomes position themselves next to each other- This is called synapsis. Crossing over occurs- This is when homologous chromosomes “swap” pieces of DNA with each other.

METAPHASE I Homologous pairs line up along the midline of the cell.

ANAPHASE I Homologous chromosomes move away from each other toward opposite poles of the cell.

TELOPHASE I Nuclear membrane forms around each set of chromosomes Spindle breaks down Chromosomes do not uncoil and nucleoluses do not form because there is a second round of nuclear division. This is followed by Cytokinesis I which produces 2 haploid cells.

PROPHASE II Nuclear membrane breaks down Spindle forms

METAPHASE II Chromosomes line up in single file along the midline of the cell.

ANAPHASE II Chromatids of chromosomes separate and move to opposite poles of the cell.

TELOPHASE II Chromosomes uncoil to become chromatin. Nuclear membranes form around each set of chromosomes Nucleoluses form in each nuclear membrane. Spindle breaks down. This is followed by Cytokinesis II which produces 4 haploid cells.

Differences between mitosis and meiosis Metaphase- chromosomes are in single file 2 product cells (diploid) Somatic cells (non-sex) produced 4 phases (PMAT) Meiosis Metaphase I chromosomes are aligned as pairs 4 product cells (haploid) Sex cells (gametes) produced Synapsis and crossing over occurs during Prophase I 8 phases (PMAT 1 and 2)

BINGO 13. Centromere 14. Crossing over 15. Prophase I 16. Haploid 17. Mitosis 18. Cell plate 19. Anaphase I 20. Interphase 21. Metaphase II 22. Synapsis 23. Gamete 24. Telophase I 1. Cytokinesis 2. Metaphase I 3. Chromatid 4. Telophase II 5. Centrosome 6. Chromatin 7. Independent assortment 8. Anaphase II 9. Somatic cell 10. Cleavage furrow 11. Homologous chromosomes 12. Spindle