Post on 27-Mar-2015
Biology AHSGE
Standard VI- Mitosis and Meiosis
Biology AHSGE
CONTENT STANDARD 6. Describe the roles of mitotic and meiotic divisions during reproduction, growth, and repair of cells.
ELIGIBLE CONTENTA. Demonstrate an understanding of how
meiosis leads to variation.B. Describe the role of meiosis in producing
variation.C. Describe the role of meiosis in reproduction.D. Describe the role of mitosis in cell repair.E. Describe the role of mitosis in growth.F. Describe the role of both mitosis and meiosis.
The Cell Cycle When a eukaryotic cell reaches its size limit, it divides. Cell Cycle- Reproduction by a cycle of growing and
dividing. Three phases:
– Interphase- Cell growth, maturity, DNA duplication, and prep for division
• Chromatin (relaxed form of DNA) strands make copies of themselves
– Mitosis- Nuclear material divides and moves to opposite sides of the cell
– Cytokinesis- Cytoplasm divides, and two identical daughter cells form
The Cell Cycle
The Cell Cycle and Mitosis Purposes:
– Increase the number of cells as a young organism grows into the adult form
– Replace damaged cells Regulation: Controlled by cyclins (proteins) binding to
cyclin-dependent kinases (CDKs- enzymes)– Cancer- Uncontrolled division and growth of cells
– Carcinogen- Known to cause cancer
– Apoptosis- Programmed cell death
– Stem cells- Unspecialized cells that can develop into specialized cells
• Embryonic stem cells- First 100-150 cells from a fertilized egg
• Adult stem cells- Found in various tissues; may be used to maintain and repair those tissues
Mitosis- Prophase1. Chromatin strands tighten (condense) into
chromosomes- Sister chromatids- Identical halfs of a
chromosome - Centromere- Center of attachment
2. Nucleolus disappears 3. Spindle Fibers appear and attach to opposite
sides of centromeres and centrioles- Responsible for moving and arranging
chromosomes
4. Centrioles move to the poles- Spindle apparatus- Spindle fibers, centrioles and
aster fibers (star-like microtubules of centriole)
5. Nuclear envelope disappears
Mitosis- Metaphase
Sister chromatids are pulled by motor proteins along the spindle apparatus toward the center of the cell
Chromosomes line up in the middle, or equator, of the cell
Mitosis- Anaphase
Microtubules of spindle apparatus shorten, pulling the chromosomes in half
With the help of motor proteins, chromatid strands are pulled to opposite sides of the cell
Mitosis- Telophase
Chromatid strands arrive at ends of cell and decondense
Two new nuclear membranes form around chromatin
Nucleoli reappear Spindle apparatus
disassembles
Cytokinesis
Cytoplasm divides resulting in two cells with identical nuclei
In plants, a cell plate forms and new cell wall forms on each side
Binary fission- In prokaryotes, DNA is duplicated and copies attach to cell membrane. Membrane grows and pulls apart DNA molecules. Cell completes fission, resulting in two identical cells.
AHSGE Biology
Standard VI- Mitosis and Meiosis
Chromosomes
Traits- Characteristics passed to offspring from parents– Instructions found on chromosomes– Genes- segments of DNA found on each chromosome;
approx. 1500 per chromosome Homologous Chromosomes- Pairs of
chromosomes; one from each parent– Humans- 23 pairs; 23 from each parent
• 46 total chromosomes
Haploid Vs. Diploid Gametes- Sex cells with half the number of
chromosomes– Created to maintain the chromosome number from
generation to generation– Represented by symbol n– Haploid- A cell with n number of chromosomes– Human gametes- n = 23
Fertilization- Fusion of gametes– Results in 2n zygote (fertilized egg cell)– Diploid- A cell with 2n number of chromosomes– Human somatic (regular body cells) cells- 2n = 46
Meiosis Forms gametes with genetic variation
– Spermatogenesis- process of producing sperm with half the number of chromosomes• Undifferentiated- no flagellum
– Oogenesis- the creation of an ovum (egg cell)• three polar bodies all die (incomplete egg cells)
Reduction division- Reduces the number of chromosomes in half
– 2n ⃗ n (Diploid to haploid) Occurs in reproductive structures of sexual organisms Involves two divisions: Meiosis I and Meiosis II
Meiosis I
1. Cell undergoes Interphase
2. Prophase I- Homologous chromosomes
condense and pair up (synapsis)
- Crossing over- segments or genes are exchanged during synapsis
- Centrioles move to opposite poles and spindle fibers attach to centromeres
Crossing Over
Meiosis I3. Metaphase I- Homologous
chromosomes (pairs) line up at the equator
4. Anaphase I- Homologous chromosomes separate and move towards opposite poles (disjunction)
- Reduces chromosome number from 2n to n
- Independent Assortment- random segregation and assortment of chromosomes during gametogenesis (production of gametes); aids in increasing genetic diversity
Meiosis I
5. Telophase I- Individual chromosomes arrive at opposite poles
– Cytokinesis occurs
– Nuclear membrane and nucleoli reappear
– Two new cells formed, each with new genetic variation
Meiosis II
1. Prophase II- Occurring in two cells
- Chromosomes condense- Nucleolus disappears - Spindle Fibers appear
and attach to opposite sides of centromeres and centrioles
- Centrioles move to the poles
- Nuclear envelope disappears
Meiosis II
2. Metaphase II- Sister chromatids are pulled by motor proteins along the spindle apparatus to line up at the equator
Meiosis II
3. Anaphase II- Microtubules of spindle apparatus shorten, pulling the chromosomes in half and to opposite sides of the cell
Meiosis II
4. Telophase II- Chromatid strands arrive
at ends of cell and decondense
- Two new nuclear membranes form around chromatin
- Nucleoli reappear
- Spindle apparatus disassembles
- Cytokinesis occurs
- Four unique, haploid (n) gametes result
Mitosis Meiosis
One division Two divisions: Meiosis I and II
DNA replication in Interphase
DNA replication once in Meiosis I
Synapsis doesn’t occur Synapsis occurs
Two identical, diploid cells Four different, haploid cells
Somatic cells Reproductive cells
Growth and repair Gametes & genetic variation