Cellular Reproduction Cellular reproduction occurs in both Eukaryotic and Prokaryotic cells Cellular reproduction in multicellular organisms is important for growth and to insure the survival of that species. Cellular reproduction in unicellular organism is only important for the survival of that species. When cells reproduce they go through a process called cell division

Reproduction of Organisms Cells that divide in multicellular organisms to produce sex cells for sexual reproduction is called meiosis (we’ll discuss later). Unicellular organism divide asexually to produce their offspring Asexual reproduction include - binary fission (bacteria) - budding (yeast) binary fission budding

Cell Division: Mitosis & Cytokinesis In Eukaryotic cells, cell division has two parts called mitosis and cytokinesis Mitosis is the process by which the nucleus of the cell is divided into two new nuclei, each nucleus with same number and kinds of chromosomes as the parent cell. Cytokinesis is the process by which the cytoplasm divides, thus forming two distinct cells. Mitosis Cytokinesis

Chromosomes Chromosomes are structures in the nucleus of a cell that contain genetic (DNA) information that is passed on from one generation to another. After DNA replication the chromosomes become visible. As seen in the diagram to the right a chromosome is made up of two identical parts (Chromatids or Sister Chromatids) Each chromatid is attached to each other at the center called a centromere

Chromosomes and their numbers The parents cells of an organism contain a certain number of chromosomes. We called this number the Diploid number.  Diploid cells have two complete sets of chromosomes, one set inherited from each parent.The diploid is often abbreviated as 2n.  Daughter cells that develop from parent cells can have a diploid number (2n) of chromosomes or a haploid number (n) of chromosomes  Haploid cells have half the usual number of chromosomes, or only one chromosome set. parents cells (always diploid) Daughter cells or diploid Daughter cells haploid

Cells and their Chromosomes Somatic cells (all body cells except reproductive cells) are diploid as parent cells and diploid as daughter cells. Germ cells (reproductive cells) are diploid as parent cells and haploid as Gametes (daughter sex cells). Male gametes are sperm, female gametes are the egg cell.

The Cell Cycle The cell cycle is the period from the beginning of one mitosis to the beginning of the next. Notice the Blue area on the outside called interphase. Notice the Red area on the outside called mitosis. These two areas make up the cell cycle. Notice at the end of mitosis two new cells are produced.

Interphase Cytoplasm The longest period of the cell cycle. The cell spends about 3/4 of the cell cycle time in interphase Not considered part of mitosis, sometimes call the “resting stage”, but it is actually a period of intense activity. Interphase is divided into three phases: G1, S, G2. Each is characterized by specific events G1or gap 1, growth occurs The S phase DNA replication occurs, along with protein synthesis. G2 or gap 2, preparation for cell division occurs Nucleolus Chromatin Interphase The S phase

Mitosis: Prophase The longest phase of mitosis. Sister Chromatids become visible. (Notice the number of chromatids/chromosomes is 4) The centrioles, separate from each other and take position on the opposite sides of the nucleus. Centrioles form spindle fibers, a meshlike structure made of tubulin, a microtuble protein helps move the chromosomes. The nucleolus disappear and the nuclear membrane break down. centriole Sister Chromatids spindle fibers nuclear membrane

Metaphase The shortest phase of mitosis. The sister chromatids line up across the center (MIDDLE) of the cell. Microtubles connect the centromere of each chromatids to the poles of the spindle. Because of their starlike arrangement around the poles of the spindle, these microtubules are called asters. asters Centromere

Anaphase Begins when the centromeres that join the sister chromatids split. The sister chromatids separates forming individual chromosomes, the two set of chromosomes move to opposite poles Biologists are not sure what provides the force that separates the chromosomes. chromosomes

Telophase The End or Final stage of mitosis The chromosomes, which have been distinct and condensed, now begin to uncoil into a tangle of chromatin. the nuclear membrane reforms around the chromatin, the spindle begins to break apart and a nucleolus becomes visible. Notice that the number of chromosomes, (4) is the same as when mitosis started.

Cytokinesis This is the physical division of the cytoplasm of eukaryotic cells into two daughter cells after mitosis. Animal cells divide when microfilaments pull past one another, decreasing the diameter of the cell and creating a cleavage furrow around the circumference of the cell. daughter cells cleavage furrow

Cytokinesis con’t Plant cells divide by forming a cell plate of cellulose, which lays down along the membrane, dividing the cytoplasm into two parts and forming a cell wall between the daughter cells. cell plate

Plant Cell Mitosis

Use these terms and label the phases of mitosis and identify the different structures in the diagrams. prophase metaphase telephase interphase anaphase chromosome centriole spindles centromere

What is the correct order of the stages of mitosis shown above? J 4 – 2 – 1 – 3 Which figure shows the last stage of mitosis? A Figure 1 B Figure 2 C Figure 3 D Figure 4

Meiosis Meiosis is the cell division in which the number of chromosomes is halved during the formation of gametes (haploid cells). The gametes (n) are produced by a process called meiosis which involves two divisions. All cells within the body of a sexually reproducing organism originated from a single fertilized egg. Variations of genes occur when the exchange of chromosome segments (crossing over) take place during prophase 1. Reproduction involves the fusing of two gametes (n) (fertilization) to produce a zygote (2n).

Differences between Mitosis and Meiosis One division only 2 daughter cells All daughter cells contain a diploid number (2n) of chromosomes Chromosomes line up randomly on the central plane Chromatids separate Two divisions 4 daughter cells All daughter cells contain a haploid number (n) of chromosomes Chromosomes line up in pairs on the central plane Chromosome pairs separate in the first division followed by the separation of the chromatids in the second division

Mitosis vs Meiosis greatest number of chromosomes Parent Cell of Mitosis somatic cells = diploid (2n) body cells = diploid (2n) root cells = diploid (2n) liver cells = diploid (2n) Daughter Cell of Mitosis all are diploid (2n) Parent Cell of Meiosis germ cell = diploid (2n) Daughter Cell of Meiosis sex cells = haploid (n) gametes = haploid (n) sperm = haploid (n) egg (ovum) = haploid (n) Fertilization of sex cells zygote = diploid (2n)

Zygote Development via Mitosis