Chapter 8 – Cellular Reproduction

In order for organisms to grow and reproduce, cells must divide.

Cell Division (8.1)

Cell division is part of asexual reproduction Single-celled organisms reproduce by simple cell division There is no fertilization of an egg by a sperm

Sexual reproduction Requires fertilization of an egg by a sperm using a special type of cell division called meiosis. Thus, sexually reproducing organisms use: – Meiosis for reproduction – Mitosis for growth and maintenance

Chromosomes Contain Our Genes Long stretches of DNA and proteins Humans have 23 different chromosomes Diploid – 2 of each chromosome (our body cells) Haploid – 1 of each chromosome (our sex cells)

Duplicated chromosomes (sister chromatids) TEM Tight helical fiber Looped domains TEM Centromere Nucleosome “Beads on a string” Histones DNA double helix Figure 8.4

Chromosomes 8.2

Cell Cycle 1.Cells grow and do “cell” things 2.Cells copy DNA 3.Each copy moves to opposite ends of cell. 4.Cells divide; each new cell has a copy of DNA

Chromosomes are duplicated before cell division

Cell Cycle (8.6)

Eukaryote cells divide by mitosis or meiosis Mitosis – One cell divides producing two identical nuclei followed by cell division – Almost all cell reproduction Meiosis (only in testes and ovaries) – One cell divides twice to produce four genetically different cells – Produces egg and sperm cells (gametes)

A Cell’s life cycle is divided into phases. Most of the time a cell is in Interphase During interphase, a cell: – Performs its normal functions – Doubles everything in its cytoplasm – Grows in size

Interphase and Prophase (8.7)

Prophase Chromosomes condense and are visible under light microscope Nuclear membrane breaks down Spindle microtubules grow from two centrosomes, clouds of cytoplasmic material that in animal cells contain centrioles.

Metaphase and Anaphase Metaphase Mitotic spindle guides the separation of two sets of daughter chromosomes. Chromosomes line up along middle axis of cell (metaphase plate) Anaphase Spindle fibers pull the chromosomes away from center Centromeres break and each sister chromosome goes to opposite poles of the cell.

Telophase and Cytokinesis Chromosomes unwind at the poles New nuclear membrane forms Cytokinesis typically: – Occurs during telophase – Divides the cytoplasm – Is different in plant and animal cells

Cytokinesis (8.8)

Meiosis Two cell divisions (Meiosis I and II) Four daughter cells result each containing half of the chromosomes as the parent cell In males meiosis results in the production of 4 sperm cells In females meiosis results in the production of 1 large egg cell and 3 small polar bodies

Multicellular diploid adults (2n  46) MEIOSIS FERTILIZATION MITOSIS 2n2n and development Key Sperm cell n n Diploid zygote (2n  46) Diploid (2n) Haploid (n) Egg cell Haploid gametes (n  23) Figure 8.12

Meiosis has two stages Meiosis I Meiosis II

Meiosis I Similar to mitosis except during first metaphase chromosome pair up side by side During first anaphase one set of chromosomes move to either pole of the cell. Sister chromotids stay joined in the new daughter cells

Meiosis I (8.14)

Meiosis II Anaphase II sister chromotids separate Daughter cells have only one of each chromosome (Haploid)

Meiosis II (8.14)

Crossing Over Increases Genetic Variation

The number of times a cell can divide is limited.

Cloning (NIB)

Dolly was euthanized When chromosomes replicate they lose part of their ends (telomeres) Linked to aging Dolly’s chromosomes came from an adult sheep with already shortened telomeres Dolly developed age-related illnesses

Dolly taught us a lot about cellular aging.

Mitosis and Meiosis