Mitosis & Meiosis. Diploid cells- (2n)- a cell that has 2 of each chromosome - 1 from mom, 1 from dad = 1 pair

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1 Mitosis & Meiosis Diploid cells- (2n)- a cell that has 2 of each chromosome - 1 from mom, 1 from dad = 1 pair The pair is called homologous chromosomes The homologous chromosomes contain the same gene placement, but do not carry identical gene codes Humans have 23 pairs or 46 chromosomes Haploid cells- (n)- contains 1 of each kind of chromosome (1/2 of a homologous pair)

2 Cell Size Diffusion limits cell size the organism would die before the center of the cell got the materials it would need Amount of DNA limits cell size if the cell was bigger, the nucleus could not keep up with the cell s protein demands Surface area to volume ratio limits cell size as volume increases surface area increases, but surface area does not increase as much as needed

3 Mitosis Cellular Reproduction Chromosomes are dark staining structures that contain genetic information - X Chromosomes are condensed chromatin (the chromatin becomes tightly packed for ease in division) Chromatin is loosely coiled DNA in the nucleus

4 Mitosis Cellular Reproduction The Cell Cycle made up of interphase, mitosis and cytokinesis

5 Interphase The cell spends the majority of its life in interphase 3 parts of interphase gap 1 phase- cell undergoes intense growth cell grows in size, busiest phase synthesis phase- chromatin (DNA) copied gap 2 phase- cell prepares for cell division extra mitochondria and other organelles are made

6 Interphase

7 Mitosis period of nuclear division 4 stages: Prophase, Metaphase, Anaphase, Telophase The end result is 2 daughter cells that are identical to the parent cell

8 Prophase first and longest phase of mitosis chromatin coils to form chromosomes (they look like X under the scope) each half of the chromosome (X) is called a sister chromatid sister chromatids are exact copies of each other sister chromatids are held together by a centromere centromeres help with movement of the chromosomes during mitosis (cohesins) the centrioles begin to migrate to opposite poles of the cell the spindle forms (spindle- football shaped structure made of thin microtubule fibers)

9 Prophase

10 ProMetaphase chromatin continues to coil the nuclear envelope & nucleolus disintegrate microtubules of the spindle invade the nuclear area some microtubules attach to the kinetochore at the centromere

11 Prometaphase

12 Metaphase chromosomes attach to the spindle fibers by their centromeres chromosomes line up on the equator each sister chromatid is attached to its own spindle fiber; the spindle fiber is attached to a pole

13 Metaphase

14 Anaphase separation of sister chromatids centromeres split the spindle shortens and pulls apart the sister chromatids (pulls the X s apart) the sister chromatids begin migration to opposite poles

15 Anaphase Telophase

16 Telophase final phase: the reverse of Prophase sister chromatids reach opposite poles chromosomes unwind to chromatin spindle breaks down nucleolus reappears cytoplasm pinches to form 2 cells: this is called cytokinesis (animal cell only) cell plate forms across the cell s equator in a plant cell; the cell membranes and cell walls then form

17 Results of Mitosis 2 new identical cells unicellular organisms use mitosis for reproduction multicellular organisms can form tissues, organs, organ systems Cancer- uncontrolled reproduction of cell

18 Mitosis in Action

19 Onion Mitosis

20 Animal mitosis Prophase Prometaphase Metaphase Anaphase Telophase

21 Meiosis Meiosis- the formation of gametes (haploid cells) Gametes are sex cells- egg or sperm Why does meiosis occur? Why do we need to half the number of chromosomes given to our offspring? - If we received 46 chromosomes from mom and 46 chromosomes from dad, we would have 92 chromosomes!!!

22 Chromosomes replicate Interphase

23 Prophase I spindle forms DNA condenses to form tight chromosomes Synapsis occurs = tetrads formhomologous chromosomes pair up crossing over occurs exchange of genetic material between homologous pairs provides genetic variability = genetic recombination

24 Metaphase I centromere of each chromosome attaches to the spindle spindle fibers pull tetrads to the equator (tetrads line up together)

25 Anaphase I Anaphase I & Telophase I tetrads (homologous pairs) separate Telophase I chromosomes uncoil to form chromatin spindle breaks down cytoplasm divides

26 Prophase II spindle forms spindle attaches to chromosomes at the centromeres

27 chromosomes line up at the equator Metaphase II

28 Anaphase II centromeres split sister chromatids separate & move to opposite poles

29 spindles break down nucleus reforms and cytoplasm divides Meiosis produces 4 haploid cells. The 4 cells are genetically different Telophase II

30 Meiosis II

31 Meiosis Overview

32 Meiosis Mistakes Nondisjunction- failure of homologous chromosomes to separate during meiosis. Trisomy- the zygote produced has an extra chromosome Ex: down syndrome Monosomy- the zygote produced lacks a chromosome Ex: turner syndrome (1 X chromosome); death Triploidy- the zygote has 3 sets of chromosomes Polyploidy- the zygote has more than 1 copy of the chromosomes; results in death in most animals, but is beneficial in some plants

33 Meiosis

34 Meiosis Mistakes Triploidy Karyotype- An organized picture of the chromosomes of an organism Homologous chromosomes are paired together and arranged from largest to smallest

35 Sexual Reproduction Sexual reproduction uses sex cells and results in a zygote. A zygote is the fusion of an egg cell and a sperm cell.

36 Asexual Reproduction Binary Fission Budding Fragmentation

37 Binary Fission Process by which bacteria cells reproduce. 1. DNA attaches to cell membrane 2. DNA duplicates 3. Second DNA strand attaches to cell membrane 4. Cell continues to grow 5. Cell splits into two separate cells