- Slides: 26
MITOSIS AND MEIOSIS Cell Division
MITOSIS ASEXUAL division of a cell Occurs in EUKARYOTIC cells (they HAVE a nucleus) Makes a clone n A CLONE is a genetically identical copy
MITOSIS Produces offspring with the full DIPLOID number of chromosomes. n Ex. In a fruit fly, there are 8 chromosomes, so our diploid number (2 n) is 8. 2 n 2 n 2 n
MITOSIS “Offspring” (daughter cells) are genetically identical to the “parent” cell. In humans, mitosis is used for growth and repair of body tissues. n Ex. If you have a cut, mitosis is what helps the cut to heal.
STAGES OF MITOSIS INTERPHASE n n This “stage” is where the cell spends most of it’s “life”. The cell prepares for division by making an exact copy of each chromosome. (replication)
STAGES OF MITOSIS PROPHASE n n n The chromosomes become visible. The nuclear membrane begins to disappear. The SPINDLE FIBERS form between CENTRIOLES.
STAGES OF MITOSIS METAPHASE n n The chromosomes “line up” in the middle of the spindle. Spindles attach to centromere
STAGES OF MITOSIS ANAPHASE n n The chromosomes begin to separate When they separate, each piece becomes a CHROMATID.
STAGES OF MITOSIS TELOPHASE (in ANIMAL cells) n Two new cells begin to form by pinching in (cleavage) at the membrane. CYTOKINESIS-the division of cytoplasm
STAGES OF MITOSIS TELOPHASE (in PLANT cells) n Instead of pinching in, a CELL PLATE forms between the two daughter cells.
3 REASONS MITOSIS OCCURS 1. As the cells divide, the organism increases in size. 2. In humans, mitosis occurs to replace dead red blood cells (about every 120 days). 3. Asexual cellular reproduction n Ex. Amoeba
MEIOSIS Sexual reproduction (involves 2 parents) Makes sex cells (gametes) n These gametes are __________(male) __________(female) The gametes are made in the gonads. n The gonads are ____________(males) ____________(females)
MEIOSIS All meiosis occurs in the GONADS Purpose: n To reduce the chromosome number so when 2 gametes combine (fertilization), a zygote is formed.
MEIOSIS Picture of GAMETOGENESIS
MEIOSIS Oogenesis n n n Occurs in the ________ Forms of 1 egg and 3 polar bodies The egg has half the chromosome number as the parent cell. (haploid number) Spermatogenesis n n n Occurs in the ________ Produces 4 sperm cells Each sperm has half the chromosome number of the parent cell. (haploid number)
MEIOSIS Chromosome numbers are reduced during meiosis. n Examples: If a body cell has 46 chromosomes, the gamete will have _______. If a dog’s skin cell has 72 chromosomes, each sperm cell will have _______. If a liver cell has 32 chromosomes, how many chromosomes does the egg cell have? _____ If an alligator has 14 chromosomes in its sperm, how many chromosomes are in his mates egg cell? ______ If the haploid number is 23, then the diploid number is _____.
MEIOSIS Recombination of chromosomes causes GENETIC VARIATION. Picture of fertilization
MEIOSIS Meiosis is called reduction-division of chromosomes because the chromosome number is reduced and replicated before the cell divides. n n Diploid Haploid 2 N N
MEIOSIS Steps of meiosis: Meiosis I and Meiosis II n During Meiosis IInterphase n Chromosomes pair up to form homologous pairs. Prophase n Spindle forms and nuclear membrane disappears Metaphase n n n Homologous Pairs line up in the middle of the spindle This is called SYNAPSIS A TETRAD is formed (sister chromatids) Anaphase n n Homologous Pairs are separated from one another This is called DISJUNCTION Telophase n n Cytoplasm divides Each cell has the monoploid (haploid) number of chromosomes
MEIOSIS Steps of meiosis: Meiosis I and Meiosis II n During Meiosis IIProphase II n Spindle forms and nuclear membrane disappears Metaphase II n Chromosomes line up in the middle of the spindle. Anaphase II n Chromosomes are pulled apart by spindles. Telophase II n Cytokinesis (cytoplasm divides) and four DAUGHTER CELLS are formed (in males). * *In females, only ONE viable monoploid cell is produced.
MITOSIS AND MEIOSIS