Cell division All cells arise from other cells A cells life cycle is an alternation between Interphase and mitosis Interphase is an active period where there are many biochemical reactions cell growth DNA transcription DNA replication spans most of the life of the cell

Cell division Mitosis is the process of dividing one cell into two cells which each has the same number of chromosomes as the parent cell during the first part of mitosis the chromosomes condense and become visible in the light microscope they are two copies of the original chromosome

Cell division the chromosomes become attached to microtubules and align themselves in the middle of the cell each chromatid is drawn by the microtubules to the opposite ends of the cell the cytoplasm is then divided in two in the middle and a nucleus forms in both the cells two new cells have formed that have genetically identical nuclei

Cell division Gametes (sex cells) are haploid. A haploid cell has only one copy of each chromosome. It is said to have n number of chromosomes All cells except gametes are diploid. A diploid cell has two copies of each chromosome. It is said to have 2n number of chromosomes

Cell division In mitosis one 2n cell divides into two 2n cells One diploid cell Two diploid cells with genetically identical nuclei 2n

Cell division Karyotype is an individuals particular array of chromosomes. A normal human karyotype consists of 46 (2n) chromosomes or in other words 23 (n) pairs.

Cell division Meiosis is a reduction division a diploid cell divides into four haploid cells this involves two rounds of nuclear divisions nn 2n nn Meiosis I Meiosis II (DNA replication)

Cell division Meiosis I During this stage the double chromosomes form pairs One double chromosome of each pair can go to either daughter cell Chromosomes #2 Chromosomes #3 from father from mother

Cell division Meiosis II During this stage the double chromosomes divide with one part going into each cell One part of each chromosome can go to either daughter cell nn

Cell division Meiosis II Non-disjunction can lead to changes in chromosome number One chromosome does not let go of both chromatides and stays together n plus an extra chromosome n minus one chromosome

Cell division Explain how the movement of chromosomes during meiosis can give rise to genetic variety in the resulting haploid cells? A cell with n = 2 can have how many different combinations? A cell with n = 3 can have how many different combinations?

Meiosis - Mitosis

Cell division Interphase precedes mitosis and the doubling of the genetic material has taken place, through replication. Centrioles are also replicated. Mitosis is divided into four main phases: Prophase - metaphase - anaphase - telophase Followed by Cytokinesis: it is the cleavage of the cytoplasm and the formation of new cell membranes.

Cell division In plant cells There are no centrioles (centrosomes) but still a mitotic spindle forms. During cytokinesis the rigid cell wall prevents the pinching that happens in animal cells. Instead membrane components assemble in the interior and a cell plate grows outward until it fuses with the cell membrane. Cellulose is the laid down along the new membranes.