Mitosis
Mitosis results in a parent cell dividing into two daughter cells. The genetic material in the daughter cells is identical. The main purpose of mitosis is to support growth and replace worn out cells. Mitosis occurs in all organisms except viruses.
Mitosis results in a parent cell dividing into two daughter cells. The genetic material in the daughter cells is identical. The main purpose of mitosis is to support growth and replace worn out cells. Mitosis occurs in all organisms except viruses.
- Interphase- the period between cell divisions
- During Interphase, the chromosomes replicate- each DNA strand unzips into two strands while free-floating bases attach to the unzipped strands. The two pairs of centrioles help with cell reproduction.
- The chromosomes begin to condense into two identical copies called sister chromatids.
- Spindles begin to form from the centrioles. The spindles are made of fibers.
- The centrioles begin to separate. The nuclear membrane begins to crack and disperse.
- The centrioles are at opposite ends of the cell.
- The spindle fibers from both centrioles attach to each chromosome.
- The chromosomes line up on the metaphase plate, where the cell divides in two.
- Fibers begin to tug each chromosome towards opposite ends of the cell.
- The sister chromatids break apart. The fibers pull the chromatids towards opposite ends of the cell.
- The chromatids, which are now also considered chromosomes, arrive at the opposite ends of the cell and new nuclear membranes form.
- Mitosis, which describes only the division of the nucleus, is now complete.
- The rest of the cell divides!
- Cytokinesis- division of the cell's cytoplasm.
Meiosis
Sperm and eggs have 23 chromosomes each. If each of those gamete cells had 46 chromosomes (the genetic code of a human being is contained within 46 chromosomes), a fertilized egg would contain 92 chromosomes and be untenable. Meiosis avoids this by halving the number of chromosomes in a cell. Meiosis is specific to reproduction and causes a cell to divide twice resulting in 4 cells. Each of these cells will have only half the number of chromosomes (23), but each chromosome will contain genetic information from both parents.
Sperm and eggs have 23 chromosomes each. If each of those gamete cells had 46 chromosomes (the genetic code of a human being is contained within 46 chromosomes), a fertilized egg would contain 92 chromosomes and be untenable. Meiosis avoids this by halving the number of chromosomes in a cell. Meiosis is specific to reproduction and causes a cell to divide twice resulting in 4 cells. Each of these cells will have only half the number of chromosomes (23), but each chromosome will contain genetic information from both parents.
- Interphase I-the period between cell divisions
- The activity within the cell is the same as in mitosis!
- The activities are pretty much the same as in mitosis, except that in this cell the chromosomes attach to the nuclear membrane.
- The chromosomes then pair up with their corresponding chromosome (mom and dad chromosomes pair up).
- Enzymes cut genes from the chromosomes. Those DNA sequences are exchanged between the genes.
- Same as in mitosis except the spindle fibers attach to one chromosome of a matching pair.
- Fibers from one centriole attach to 23 chromosomes and fibers from the other centriole attach to the other 23.
- Pairs line up on either side of the metaphase plate and the fibers begin to tug them to opposite ends of the cell.
- Chromosome pairs separate; half go to one end of the cell and half go to the other.
- Sister chromatids do not split like they do in mitosis.
- The chromosomes arrive at opposite ends of the cell and new nuclear membranes form.
- In female meiosis, cytoplasm will be concentrated more in one of the two emerging eggs. This results in one larger egg and one smaller egg. The small cell degenerates and the large cell divides again.
- This stage identical to the one in mitosis.
- The chromosomes do not replicate during this phase, as they do in interphase in mitosis and interphase I in meiosis.
- The chromosomes condense, spindles form, the centrioles separate, and the nuclear membrane fragments and disperses.
- The chromosomes do not attach to the nuclear membrane to exchange genetic material like they do in Prophase I.
- Spindle fibers attach to the chromosomes. The centrioles are at opposite ends of the cell.
- Fibers from both ends attach to each one of the four chromosomes.
- The chromosomes align along the metaphase plate.
- Like in mitosis metaphase, the fibers from the centrioles begin to pull on each of the chromosomes from both directions.
- The fibers pull the chromatids apart and towards opposite ends of the cell.
- The chromatids arrive at either end of each cell and new nuclear membranes form.
- The rest of the cell divides.
- Only when two, distinct cells form, will cytokinesis be complete.
- There are now four daughter cells. Each cell has one set of chromosomes, or one half the number of the initial cell.