Cell Division: Meiosis vs. Mitosis

Описание: MEDICAL ANIMATION TRANSCRIPT: Mitosis is a type of cell division with many vital functions, including embryonic development, promoting tissue growth after birth, and replacing damaged or dying cells in the body. In mitosis, there is one division, and the resulting two daughter cells contain the same number of chromosomes as the parental cell. These cells are called diploid cells because they contain 23 pairs of chromosomes, with each pair containing one maternal and one paternal chromosome. After DNA replication, mitosis begins with prophase, during which chromatin condenses into chromosomes, each consisting of two identical sister chromatids. The nuclear envelope dissolves, and spindle fibers begin to grow from the cell's centrioles. During metaphase, the spindle fibers pull the chromosomes into alignment in the center of the cell. In anaphase, each chromosome, consisting of two genetically identical chromatids, splits in two. Each chromatid, now considered a single-stranded daughter chromosome, migrates to the opposite end of the cell from its twin. During telophase, nuclear envelopes reform around the chromosomes as the cell finishes dividing. Meiosis is a type of cell division with one purpose - to produce eggs and sperm called gametes. In meiosis, there are two divisions in succession, resulting in four daughter cells. Each daughter cell contains half the number of chromosomes of the initial parental cell. The daughter cells are called haploid cells because they contain 23 unpaired chromosomes. After DNA replication, the first cell division, or meiosis I, begins with prophase I, during which chromosomes condense. Late in prophase I, chromatids in each pair break and exchange corresponding sections of DNA in a process called crossing over, thus creating new combinations of genes. During metaphase I, homologous chromosome pairs line up in the center of the cell. Each pair can line up randomly from left to right in a process called independent assortment. In anaphase I, each pair of chromosomes separates, and in telophase I, the cell divides, resulting in two haploid daughter cells. The second meiotic division, or meiosis II, begins with prophase II, during which the cell prepares to divide again. In metaphase II, the chromosomes line up in the center of the cell. During anaphase II, each chromosome is pulled apart into two sister chromatids, each now considered a single-stranded chromosome. In telophase II, the two cells divide, resulting in four haploid daughter cells. Once meiosis is complete, the male and female gametes each contain a unique set of 23 single-stranded chromosomes, ultimately resulting in the genetic variability of humans. Once these gametes meet, they become a single fertilized cell called a zygote. The zygote has 46 chromosomes and continues to develop using mitosis.

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