Cell Reproduction

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

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

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. 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. Haploid (gamete) – A cell that does not contain chromosome pairs. The sperm and egg are haploid and, in humans, have 23 chromosomes.sperm eggsperm egg

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

Cell CycleCell 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. Mitosis or Meiosis Cytokinesis Interphase

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. Cytokinesis occurs differently in animal and plant cells. In animal cells, the cell membrane pinches in until it eventually splits the cell into two. In animal cells, the cell membrane pinches in until it eventually splits the cell into two. This pinching in is called a cleavage furrow. 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. 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. 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: Each student kit needs: –one 8 foot orange string cut in ½ –One 5 foot black string cut in ½ –1 clear spoon and fork –1 white spoon and fork –2 pom-poms –2 paper clips –8 coffee stirrers

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. A type of cell division in which the chromosome # is reduced by half to produce haploid cells. This produces gametes (sex 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. 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 Nuclear membrane breaks down Nucleolus breaks down Nucleolus breaks down Mitotic spindle forms from the centrosomes Mitotic spindle forms from the centrosomes Chromatin coils to become chromosomes Chromatin coils to become chromosomes Homologous chromosomes position themselves next to each other- This is called synapsis. 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. 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. 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. Homologous chromosomes move away from each other toward opposite poles of the cell.

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

PROPHASE II Nuclear membrane breaks down Nuclear membrane breaks down Spindle forms Spindle forms

METAPHASE II Chromosomes line up in single file along the midline of the cell. 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. Chromatids of chromosomes separate and move to opposite poles of the cell.

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

Differences between mitosis and meiosis Mitosis Mitosis –Metaphase- chromosomes are in single file –2 product cells (diploid) –Somatic cells (non- sex) produced –4 phases (PMAT) Meiosis 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)

What if meiosis yields sex cells with 23 chromosomes? Down Syndrome Down Syndrome Down Syndrome Down Syndrome Turner Syndrome Turner Syndrome Turner Syndrome Turner Syndrome Klinefelter Syndrome Klinefelter Syndrome Klinefelter Syndrome Klinefelter Syndrome