Cell Division How to make more

What we are going to investigate. A review of the structure of the chromosome A review of the structure of the chromosome Why cells divide Why cells divide Mitosis Mitosis Meiosis Meiosis Cancer cells Cancer cells Genetic Variation associated with cell division Genetic Variation associated with cell division Diseases of non- disjunction Diseases of non- disjunction

Why do we need to learn this? So that we can understand how our bodies work. So that we can understand how our bodies work. So we can have a deeper understanding of how reproduction really works and what can go wrong. So we can have a deeper understanding of how reproduction really works and what can go wrong. To understand how some genetic disorders arise. To understand how some genetic disorders arise. So that when you or any of the multicellular organisms around you have offspring, you understand where their genetic material comes from. So that when you or any of the multicellular organisms around you have offspring, you understand where their genetic material comes from.

Review What are the parts of a chromosome?

Genes A Gene is a sequence of DNA that instructs a cell to produce proteins A Gene is a sequence of DNA that instructs a cell to produce proteins It is the unit of inheritance It is the unit of inheritance

DNA DNA (Deoxyribonucleic Acid) DNA (Deoxyribonucleic Acid) is the chemical whose building block sequence encodes the information that a cell uses to construct a particular protein. is the chemical whose building block sequence encodes the information that a cell uses to construct a particular protein.

Structure of a Chromosome A Chromosome is a highly coiled and condensed strand of DNA wrapped around proteins called histones. A Chromosome is a highly coiled and condensed strand of DNA wrapped around proteins called histones. A Chromosome is made from a single strand of DNA and contains many genes. A Chromosome is made from a single strand of DNA and contains many genes.

Structure of a Chromosome  A Chromatid – A single, very condensed strand of DNA. Half of a chromosome.  A Centromere – The largest constriction in a chromosome. This is the place where the chromatids are held together.  A Kinetichore – The area of the chromosome where the spindle fibers attach.  A Telomere – A chromosome tip.

Chromosome Parts Kinetichore Telomere

Why do we need to make more cells? 1. Growth 2. Repair 3. Reproduction What would happen if we could not make new cells?

What happens when our cells will not stop multiplying? Cancer Understanding diseases typically requires scientists to examine basic cellular processes Understanding diseases typically requires scientists to examine basic cellular processes Uncontrolled cell division is a form of cancer Uncontrolled cell division is a form of cancer Understanding those processes can help health care workers develop better prevention and treatment strategies. Understanding those processes can help health care workers develop better prevention and treatment strategies. You have to know how something works in order to fix it!

The Cell Cycle Regular sequence of growth and division. Regular sequence of growth and division.  Cell cycle rates vary  A brain cell may never divide  Embryos divide rapidly This is a continuous process that we study in steps

Interphase Interphase is the major stage of cell division where the cell is not dividing, but there is a lot of cell activity. Interphase is the major stage of cell division where the cell is not dividing, but there is a lot of cell activity.

Interphase is divided into 3 phases  G1 (Gap phase 1)  Cell is making protein, carbohydrates, and lipids.  Time in G1 varies greatly.  S (Synthesis phase)  Cell replicates it’s genome (DNA)  Proteins that make the spindle fibers are produced.  Microtubules form centrioles near the nucleus in animal cells.  G2 (Gap phase 2)  Cell makes more proteins for membranes of daughter cells

Two Types of Cell Division Mitosis Mitosis The division of two somatic (non-sex) cells The division of two somatic (non-sex) cells Produces two identical daughter cells. Produces two identical daughter cells. Daughter cells have the same number of chromosomes as the parent cell Daughter cells have the same number of chromosomes as the parent cell Diploid chromosome # is the total chromosome # for a species Diploid chromosome # is the total chromosome # for a species Meiosis Meiosis A type of cell division that halves the usual number of chromosomes to form haploid gametes A type of cell division that halves the usual number of chromosomes to form haploid gametes A gamete is a sex cell (Sperm or Egg) A gamete is a sex cell (Sperm or Egg) Cells have half the chromosome number of the parent cell (haploid) Cells have half the chromosome number of the parent cell (haploid)

Stages of Mitosis: Prophase Microtubules assemble to form spindle Microtubules assemble to form spindle Nuclear membrane breaks down Nuclear membrane breaks down Nucleus no longer visible Nucleus no longer visible DNA is condensed DNA is condensed

Metaphase Chromosomes attach to spindle at their centromeres. Chromosomes attach to spindle at their centromeres. They line up at the center of the cell. They line up at the center of the cell.

Anaphase Cell membrane indents at middle Cell membrane indents at middle Centromeres part and chromatids move to opposite ends of the cell Centromeres part and chromatids move to opposite ends of the cell When the split occurs, each daughter cell receives one chromatid from each replicated chromosome When the split occurs, each daughter cell receives one chromatid from each replicated chromosome Cell stretches Cell stretches

Telophase Spindle falls apart Spindle falls apart Nuclear membranes form Nuclear membranes form Chromosomes thin out Chromosomes thin out Cytokinesis – organelles distributed between two daughter cells Cytokinesis – organelles distributed between two daughter cells Cells separate Cells separate Diploid cells - the two daughter cells have the same number of chromosomes as the original parent cell Diploid cells - the two daughter cells have the same number of chromosomes as the original parent cell

Cytokinesis in Plant Cells

Cytokinesis in Animal Cells

Mitosis

Meiosis Produces sex cells: Sperm and Oocyte (Egg) cells Produces sex cells: Sperm and Oocyte (Egg) cells Haploid cells -the final daughter cells have half the chromosomal number of the original parent cell. Haploid cells -the final daughter cells have half the chromosomal number of the original parent cell. Example: Human somatic cells have 46 chromosomes. Example: Human somatic cells have 46 chromosomes. Human sex cells have 23 chromosomes. Human sex cells have 23 chromosomes. Why do the sex cells only need half of the chromosomes? Why do the sex cells only need half of the chromosomes?

Homologous Pairs Chromosome pairs (one from mom and one from dad) that have the same genes in the same order but may have different alleles, or forms of the same gene. Chromosome pairs (one from mom and one from dad) that have the same genes in the same order but may have different alleles, or forms of the same gene.

Meiosis: TWO Divisions 1 st Division = Meiosis 1 1 st Division = Meiosis 1 The number of chromosomes replicates from 46 in humans to 92. When cell divides, each daughter cell has 46 chromosomes. The number of chromosomes replicates from 46 in humans to 92. When cell divides, each daughter cell has 46 chromosomes. 2 nd Division = Meiosis 2 2 nd Division = Meiosis 2 Produces four cells from the two cells formed in meiosis 1. Produces four cells from the two cells formed in meiosis 1. Daughter cells from meiosis 1 have 46 chromosomes. When they divide they form 4 cells that each have 23 chromosomes. Daughter cells from meiosis 1 have 46 chromosomes. When they divide they form 4 cells that each have 23 chromosomes. Important to note that chromosomes do not replicate in the 2 nd division. Important to note that chromosomes do not replicate in the 2 nd division.

Meiosis

Spermatogenesis The formation of sperm cells. The formation of sperm cells. Spermatogonium – diploid cell that divides through mitosis making 2 daughter cells. One continues to divide mitotically while the other becomes specialized. Spermatogonium – diploid cell that divides through mitosis making 2 daughter cells. One continues to divide mitotically while the other becomes specialized. That cell is the Primary Spermatocyte. That cell is the Primary Spermatocyte. Users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/spermatogenesis.gif

Spermatogenesis Primary Spermatocytes (A diploid cell) undergo meiosis 1 Primary Spermatocytes (A diploid cell) undergo meiosis 1 They make Secondary Spermatocytes (haploid cells) They make Secondary Spermatocytes (haploid cells) In meiosis 2 Secondary Spermatocytes divide to make Spermatids. In meiosis 2 Secondary Spermatocytes divide to make Spermatids. The Spermatid specializes and develops a tail (flagellum) The Spermatid specializes and develops a tail (flagellum) Once mature it is called a spermatozoa Once mature it is called a spermatozoa Users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/spermatogenesis.gif

Oogenesis Meiosis in the female Meiosis in the female Oogonium – diploid cell that divides during meiosis 1. Oogonium – diploid cell that divides during meiosis 1. Primary Oocyte – an Oogonium that has grown, accumulated cytoplasm, and replicated its DNA. Primary Oocyte – an Oogonium that has grown, accumulated cytoplasm, and replicated its DNA. Primary Oocyte divides into two cells: WARNING DIFFERENCE HERE!! Primary Oocyte divides into two cells: WARNING DIFFERENCE HERE!!  A Polar Body – a small cell with very little cytoplasm  A Secondary Oocyte – A much larger cell.  Both cells are haploid

Oogenesis In meiosis 2 the Polar Body divides into two small polar bodies and they are reabsorbed. In meiosis 2 the Polar Body divides into two small polar bodies and they are reabsorbed. What A Waste! The Secondary Oocyte divides to produce another polar body and a mature egg cell or Ovum. The Secondary Oocyte divides to produce another polar body and a mature egg cell or Ovum. The Ovum has a large amount of cytoplasm. The Ovum has a large amount of cytoplasm.

Comparison of Mitosis to Meiosis Mitosis 1. One Division 2. Two Daughter Cells Per Cycle 3. Daughter Cells Genetically Identical 4. Chromosomal Number of Daughter Cells the Same as the Parent Cell (2n) 5. Occurs in Somatic Cells 6. Used for Growth, Repair, and Sexual Reproduction Meiosis 1. Two Divisions 2. Four Daughter Cells Per Cycle 3. Daughter Cells Genetically Different 4. Chromosomal Number of Daughter Cells Half that of Parent Cell (1n) 5. Occurs in Gamete Production 6. Used for Sexual Reproduction and Genetic Variation

Genetic Variation Independent Assortment of Chromosomes Independent Assortment of Chromosomes Crossing-over Crossing-over Random Fertilization of an Ovum by a Sperm Random Fertilization of an Ovum by a Sperm Nondisjunction Nondisjunction

Independent Assortment of Chromosomes Homologous pairs line up randomly during metaphase 1. Homologous pairs line up randomly during metaphase 1. 50% chance of getting either option. 50% chance of getting either option.

Crossing-over Produces Recombinant Chromosomes Produces Recombinant Chromosomes

Nondisjunction