1-The Cell and Cell Division

• Meiosis is critical for sexual reproduction, as it allows for the production of gametes.
• Vacuole, Ribosomes, Centriole, Lysosome, Nucleolus, Nucleus, Cytoplasm, Rough Endoplasmic Reticulum, Mitochondrion, Smooth Endoplasmic Reticulum, Plasma Membrane, Golgi Apparatus are all parts of a cell.
• Cell division in an animal is called mitosis, which increases the number of body cells, causing the animal to grow.
• Old body cells that die are replaced by mitosis.
• Chromosomes occur in pairs in the nucleus of all body cells except the sperm and ovum, each parent contributing one-half of the pair.
• The number of pairs of chromosomes is called the diploid number, which varies from species to species but is constant for each species of animal: Cattle, Swine, Sheep, Goat 30, Horse, Donkey, Chicken, Rabbit 32, 31, 39, 22.
• During mitosis, the chromosome pairs are duplicated in each daughter cell, so they are exactly like the old cell.
• There are four typical stages in the division of the cell nucleus: prophase, metaphase, anaphase, and telophase.
• A cell that is not dividing is in the interphase stage.
• During prophase, the chromatin in the nucleus condenses into visible chromosomes, which become visible under a microscope.
• The centrosomes, which are responsible for organizing the spindle fibers, move to opposite poles of the cell.
• The nuclear envelope breaks down, allowing the spindle fibers to attach to the chromosomes.
• During metaphase, the chromosomes line up along the equator of the cell, called the metaphase plate.
• The spindle fibers, which are attached to the centromeres of each chromosome, ensure that the chromosomes are properly aligned and can be separated correctly.
• Homolog or a homologous gene is a gene inherited in two species from a common ancestor.
• Haploid refers to the presence of a single set of chromosomes in an organism's cells.
• The male gamete is called a sperm cell and the female gamete is called an ovum, or egg cell.
• This specialized type of cell division that occurs in the gametes is called meiosis.
• The chromosome pairs are homologous - the first chromosome in the sperm corresponds to the first chromosome in the ovum; the remaining chromosomes in the sperm and ovum match up similarly.
• Aging causes the animal to eventually die of old age, if it does not die from some other cause earlier.
• The production of spermatozoa is called spermatogenesis; the production of an ovum is called oogenesis.
• When they reach sexual maturity, male animals begin producing spermatozoa (sperm cells) from spermatogonia in the seminiferous tubules in the testes.
• Spermatozoa are small, with only a small amount of cytoplasm in the head that is primarily the nucleus.
• A germ cell is any cell that gives rise to the gametes of an organism that reproduces sexually.
• When cells divide through mitosis, the daughter cells have a pair of each type of chromosome, making them diploid.
• The second meiotic division acting on the secondary oocyte produces one large cell (ootid) and one small cell (second polar body).
• A spermatid is any of the four haploid cells produced by meiosis that develop into spermatozoa.
• During meiosis the chromosome pairs are divided in such a manner that each gamete has one of each type of chromosome; the gamete cell has a haploid number of chromosomes.
• Spermatogonia are the parents of spermatocytes (diploid cells that divide by meiosis to produce four spermatids).
• The second polar bodies produced are not functional and are reabsorbed.
• If each gamete was diploid, the resulting zygote would have twice as many chromosomes as its parents.
• The reproductive cells are called gametes.
• During sexual reproduction, two gametes (one sperm and one ovum) combine to form the zygote.
• The first meiotic division acts on a primary oocyte to produce two cells; one is the secondary oocyte and the other is the first polar body.
• The first meiotic division divides in the second meiotic division to produce four spermatids.
• At sexual maturity, female animals produce ova (egg cells) in the ovaries.
• The single ovum that is produced is large and contains a lot of
• The zygote that results from the union of the sperm and ovum has a diploid number of chromosomes.
• Spermatozoa develop a long flagellum or tail that gives them a high degree of motility.
• If it does, it produces two second polar bodies.