The steps leading up to meiosis are similar to those of mitosis — the centrioles and chromosomes are replicated. The amount of DNA in the cell has doubled, and the ploidy of the cell remains the same as before, at 2 n. In meiosis I, the phases are analogous to mitosis: prophase I, metaphase I, anaphase I, and telophase I below figure. Meiosis I proceeds directly to meiosis II without going through interphase. Meiosis I is unique in that genetic diversity is generated through crossing over and random positioning of homologous chromosomes bivalent chromosomes. In addition, in meiosis I, the chromosomal number is reduced from diploid 2 n to haploid n during this process.
How many chromosomes are in a sperm cell? in an egg cell? in a white blood cell?
How many chromosomes does a sperm or egg have? - kbarieru.info
Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are our sex cells — sperm in males, eggs in females. Meiosis can be divided into nine stages. These are divided between the first time the cell divides meiosis I and the second time it divides meiosis II :. Illustration showing the nine stages of meiosis. Image credit: Genome Research Limited. Cells are the basic building blocks of living things.
People have sex for pleasure, reproduction, or both. Pregnancy happens when an egg and sperm successfully meet through intercourse or in vitro fertilization. What do they look like, and how many do we all have?
Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made of protein and one molecule of DNA, which contains an organism's genetic instructions, passed down from parents. In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell. Humans have 22 of these chromosome pairs, called autosomes.