Cell Division Mechanics: Mitosis, Meiosis, and Mutations
Introduction to Cell Division
Cell division is the process in which a parent cell (the cell that is the source of other cells) divides into two or more daughter cells (identical cells that form when a cell divides).
Mitosis: The Process of Growth and Repair
Mitosis is a type of cell division where one cell divides into two genetically identical daughter cells. The main purposes of mitosis are to allow for growth, repair, and the reproduction of cells. DNA from the parent cell is replicated so that the two daughter cells have full copies of the necessary genetic information. This process creates new cells that are genetically identical to each other. This allows for growth, repair, and reproduction because the new (daughter) cells replace damaged and worn-out (old) cells.
Meiosis: Genetic Variation and Reproduction
Meiosis is a type of cell division that results in four daughter cells, each with half the amount of chromosomes the parent cell has. The main purpose of meiosis in humans is to allow for sexual reproduction and genetic variation. The process involves halving the number of chromosomes (from 46 to 23) to form gametes (reproductive cells). One gamete from each parent (sperm from males and ova from females) joins together during sexual reproduction. Each gamete contains a different set of DNA. Each contributes 23 chromosomes, so the fetus (baby) will have the usual 46. This produces a unique combination of genes, which allows for variation in species and helps with diversity.
Understanding Genetic Mutations
Mutations occur when there are changes to a cell’s DNA. This occurs when the DNA is copied incorrectly. Errors in mitosis could cause daughter cells with too many or too few chromosomes; this is called aneuploidy. This could cause cell death, diseases, and cancer. While errors in meiosis lead to gametes with extra or missing chromosomes, this could cause miscarriages, fertility problems, and health issues for the child. Most mutations occur because of errors when dividing cells, exposure to chemicals, and exposure to radiation. Mutations also occur more frequently as any organism ages. While most mutations are harmful, there are some beneficial mutations that can increase the chances of survival for an organism. For example, the first humans in Africa had dark pigments in their skin to screen out UV radiation and to decrease the rate of cancer.
Essential Cell Division Terminology
- Gene: A piece of DNA that contains instructions for certain traits; the basic unit of inheritance.
- Chromosome: A threadlike structure made up of DNA and found in the nucleus of the cell.
- DNA: A chemical that makes up the chromosomes found in the nucleus of the cell.
- Nucleus: The information center of the cell.
- Chromatid: One of the two identical halves of a chromosome, which is replicated in preparation for cell division.
- Centromere: The region of a chromosome where spindles attach. Chromosomes are counted by this.
- Spindles: Structure that pulls the chromatids to opposite ends of the cell during cell division.
- Gamete: A mature sperm or egg cell.
- Somatic cell: Any cell of a living organism, apart from the reproductive cells.
- Homologous pairs: The chromosomes are the same size and contain the same type of genes in the same locations.
- Crossing over: This occurs where chromosomes are lined up with homologous pairs and are able to transfer genetic information between each other. It makes recombinant chromosomes, allowing variety.
- Haploid cells: The presence of a single set of chromosomes in an organism’s cell. Egg and sperm cells are haploid.
- Diploid cells: The presence of two complete sets of chromosomes in an organism’s cell. Humans are diploid.