MeiosisMeiosis

Sexual ReproductionSexual Reproduction

ReproductionReproduction

ReproductionReproduction: the process by : the process by which an organism produces which an organism produces others of its same kind.others of its same kind.

Two types of reproductionTwo types of reproduction

1.1. Asexual Asexual

2.2. Sexual-requires two organismsSexual-requires two organisms

Sexual reproduction usually Sexual reproduction usually requires two organisms.requires two organisms.

Asexual ReproductionAsexual Reproduction

Two Types;Two Types;

1.1. FissionFission

2.2. BuddingBudding

RegenerationRegeneration

Asexual ReproductionAsexual Reproduction

In In asexual asexual reproductionreproduction, a new , a new organism is produced organism is produced from one organism.from one organism.

The new organism will The new organism will have hereditary have hereditary material identical to material identical to the hereditary the hereditary material of the parent material of the parent organism.organism.

Organisms with Organisms with eukaryotic cells eukaryotic cells asexually reproduce asexually reproduce by by cell division.cell division.

Asexual Asexual Reproduction:FissionReproduction:Fission Fission occurs when Fission occurs when

an organism copies an organism copies its genetic material its genetic material and then divides and then divides into two identical into two identical organisms.organisms.

Bacteria do not have Bacteria do not have a nucleus, so they a nucleus, so they can’t use mitosis.can’t use mitosis.

Bacteria reproduce Bacteria reproduce asexually by asexually by fissionfission..

Asexual ReproductionAsexual ReproductionBuddingBudding Budding is a type Budding is a type

of asexual of asexual reproduction reproduction made possible made possible because of cell because of cell division.division.

When the bud on When the bud on the adult becomes the adult becomes large enough, it large enough, it breaks away to breaks away to live on its own.live on its own.

RegenerationRegeneration Some organisms Some organisms

can re-grow can re-grow damaged or lost damaged or lost body parts.body parts.

RegenerationRegeneration: the : the process that uses process that uses cell division to cell division to regrow body parts.regrow body parts.

Sponges, planaria, Sponges, planaria, sea stars, and some sea stars, and some other organisms can other organisms can use regeneration for use regeneration for asexual asexual reproduction.reproduction.

Newt Limb regeneration

Sexual ReproductionSexual Reproduction

sexual reproductionsexual reproduction: : Two sex cells, Two sex cells, sometimes called an sometimes called an egg and a sperm, come egg and a sperm, come together.together.

Sex cells are formed Sex cells are formed from cells in from cells in reproductive organs.reproductive organs.

SpermSperm are formed in are formed in the male reproductive the male reproductive organs.organs.

EggsEggs are formed in the are formed in the female reproductive female reproductive organs.organs.

The joining of an The joining of an egg and a sperm is egg and a sperm is called called fertilizationfertilization, , and the cell that and the cell that forms is called a forms is called a zygotezygote (ZI goht). (ZI goht).

Following Following fertilization, cell fertilization, cell division begins. A division begins. A new organism with new organism with a unique identity a unique identity develops.develops.

Diploid and Haploid Diploid and Haploid CellsCellsThe human body forms two The human body forms two

types of cells:types of cells:1.1. Diploid Diploid 2.2. HaploidHaploid

Diploid Cells-Diploid Cells- Body Cells Body Cells such as brain, skin, such as brain, skin, bones, and other tissues bones, and other tissues and organs are formed and organs are formed from body cells.from body cells.

Human body cells have Human body cells have 23 pairs of chromosomes 23 pairs of chromosomes or 46 chromosomes.or 46 chromosomes.

When cells have pairs of When cells have pairs of similar chromosomes, similar chromosomes, they are said to be they are said to be diploid.diploid.

HaploidHaploid Cells-Cells- Sex cells Sex cells such as sperm and eggs.such as sperm and eggs.

Haploid cells have only Haploid cells have only halfhalf the number of the number of chromosomes as body chromosomes as body cells cells

Human Human sexsex cellscells have have only only 23 chromosomes— 23 chromosomes— one from each of the 23 one from each of the 23 pairs of similar pairs of similar chromosomes. chromosomes.

Because sex cells do not Because sex cells do not have pairs of have pairs of chromosomes, they are chromosomes, they are said to be said to be haploid.haploid.

Meiosis and Sex CellsMeiosis and Sex Cells

A process called A process called meiosismeiosis (mi OH sus) (mi OH sus) produces haploid sex cells.produces haploid sex cells.

Meiosis ensures that the offspring will have the same Meiosis ensures that the offspring will have the same diploid number as its parent.diploid number as its parent.

After two haploid sex cells combine, a diploid zygote After two haploid sex cells combine, a diploid zygote is produced that develops into a new diploid is produced that develops into a new diploid organism.organism.

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

Meiosis IMeiosis I

each each chromosome is chromosome is duplicated, just duplicated, just as in mitosis.as in mitosis.

is visible under is visible under the microscope the microscope as two as two chromatids.chromatids.

Prophase IProphase I

Each duplicated Each duplicated chromosome comes chromosome comes near its similar near its similar duplicated mate. Now duplicated mate. Now called called homologous homologous pairs.pairs.

-Half chromosomes from -Half chromosomes from one parent, half from one parent, half from the other.the other.

-Each chromosome -Each chromosome contains genes that contains genes that code for the same code for the same inherited traits: eye inherited traits: eye color, hair colorcolor, hair color

Metaphase IMetaphase I

The homologous The homologous pairs line up in pairs line up in the center of the the center of the cell.cell.

The centromere The centromere of each of each chromatid pair chromatid pair attaches to attaches to oneone spindle fiber. spindle fiber.

Anaphase IAnaphase I

Homologous pairs Homologous pairs of chromosomes of chromosomes separate and separate and move to opposite move to opposite ends of the cell.ends of the cell.

Each duplicated Each duplicated chromosome still chromosome still has two has two chromatids.chromatids.

Telophase ITelophase I

The cytoplasm The cytoplasm divides, and two divides, and two new cells form.new cells form.

Each new cell has Each new cell has one duplicated one duplicated chromosome chromosome from each similar from each similar pair.pair.

Meiosis IIMeiosis II

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

Propase IIPropase II

Chromosomes Chromosomes recondense.recondense.

A new spindle A new spindle forms.forms.

Metaphase IIMetaphase 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 IIAnaphase II

• the chromatids separate and move to opposite ends of the cell.

• Each chromatid now is an individual chromosome.

Telephase IITelephase II

• the spindle fibers disappear

• a nuclear membrane forms around the chromosomes at each end of the cell.

When When meiosis II is finished, the cytoplasm divides.