Meiosis Sexual Reproduction

Reproduction Reproduction: the process by which an organism produces others of its same kind. Two types of reproduction Asexual Sexual-requires two organisms Sexual reproduction usually requires two organisms.

Asexual Reproduction Two Types; Fission Budding Regeneration

Asexual Reproduction In asexual reproduction, a new organism is produced from one organism. The new organism will have hereditary material identical to the hereditary material of the parent organism. Organisms with eukaryotic cells asexually reproduce by cell division.

Asexual Reproduction:Fission Fission occurs when an organism copies its genetic material and then divides into two identical organisms. Bacteria do not have a nucleus, so they can’t use mitosis. Bacteria reproduce asexually by fission.

Asexual Reproduction Budding Budding is a type of asexual reproduction made possible because of cell division. When the bud on the adult becomes large enough, it breaks away to live on its own.

Regeneration Some organisms can re-grow damaged or lost body parts. Regeneration: the process that uses cell division to regrow body parts. Sponges, planaria, sea stars, and some other organisms can use regeneration for asexual reproduction. Newt Limb regeneration

Sexual Reproduction sexual reproduction: Two sex cells, sometimes called an egg and a sperm, come together. Sex cells are formed from cells in reproductive organs. Sperm are formed in the male reproductive organs. Eggs are formed in the female reproductive organs.

The joining of an egg and a sperm is called fertilization, and the cell that forms is called a zygote (ZI goht). Following fertilization, cell division begins. A new organism with a unique identity develops.

Diploid and Haploid Cells The human body forms two types of cells: Diploid Haploid Diploid Cells- Body Cells such as brain, skin, bones, and other tissues and organs are formed from body cells. Human body cells have 23 pairs of chromosomes or 46 chromosomes. When cells have pairs of similar chromosomes, they are said to be diploid.

Haploid Cells- Sex cells such as sperm and eggs. Haploid cells have only half the number of chromosomes as body cells Human sex cells have only 23 chromosomes— one from each of the 23 pairs of similar chromosomes. Because sex cells do not have pairs of chromosomes, they are said to be haploid.

Meiosis and Sex Cells A process called meiosis (mi OH sus) produces haploid sex cells.

Meiosis ensures that the offspring will have the same diploid number as its parent. After two haploid sex cells combine, a diploid zygote is produced that develops into a new diploid organism.

During Meoisis, two divisions of the nucleus occur: Meiosis I and Meiosis II

Meiosis I each chromosome is duplicated, just as in mitosis. is visible under the microscope as two chromatids.

Prophase I Each duplicated chromosome comes near its similar duplicated mate. Now called homologous pairs. -Half chromosomes from one parent, half from the other. -Each chromosome contains genes that code for the same inherited traits: eye color, hair color

Metaphase I The homologous pairs line up in the center of the cell. The centromere of each chromatid pair attaches to one spindle fiber.

Anaphase I Homologous pairs of chromosomes separate and move to opposite ends of the cell. Each duplicated chromosome still has two chromatids.

Telophase I The cytoplasm divides, and two new cells form. Each new cell has one duplicated chromosome from each similar pair.

Meiosis II The two cells formed during meiosis I, now begin meiosis II.

Propase II Chromosomes recondense. A new spindle forms.

Metaphase II Chromosomes move to the center of the cell. Unlike what occurs in metaphase I, each centromere now attaches to two spindle fibers instead of one.

Anaphase II the chromatids separate and move to opposite ends of the cell. Each chromatid now is an individual chromosome.

Telephase II the spindle fibers disappear a nuclear membrane forms around the chromosomes at each end of the cell. When meiosis II is finished, the cytoplasm divides.