UNIT 8: REPRODUCTION PART 1: CELL DIVISION: MITOSIS AND ASEXUAL REPRO.

Introduction

Key Questions 1. Why do body-type cells need to reproduce, and how is this accomplished? 2. Why do organisms that reproduce asexually normally produce identical offspring? 3. Why do sex cells contain ½ the normal number of chromosomes, and how are these cells created?

Reproduction MITOSIS:  Used for growth and tissue repair and for asexual reproduction.

FACT! Each minute your body needs to make about 300 MILLION NEW CELLS! It does so by the process of MITOSIS!!!

How does Mitosis work???  Before a cell divides, it first COPIES (replicates) its genetic material  Then, the nucleus divides by MITOSIS  Then, the cytoplasm divides to form 2 new cells (CYTOKINESIS)

Reproduction Result of Mitosis:  Formation of 2 new genetically identical daughter cells from 1 parent cell.

Reproduction I. Stages of Mitosis in Animals: PMAT

Reproduction 1. INTERPHASE Phase cell is in when NOT going through mitosis.  Performing metabolic activities to maintain homeostasis and growing in size DNA is in form of chromatin  “2n” refers to the “normal chromosome number”

Reproduction If cell is to go through mitosis, it must prepare by REPLICATING the chromosomes.  The chromatin doubles, so now there are 2 identical copies of the genetic material.  2n x 2 = 4n (what is in the cell now)

Draw Interphase Nuclear Membrane (disappears) Chromatin (doubles)

Reproduction 2. PROPHASE  Doubled chromatin reorganizes into chromosomes – becomes shorter and coiled  2 pairs of centrioles move to opposite sides (or poles) – act as anchors

Reproduction Prophase Continued:  Centrioles produce mitotic spindle and begin to move to opposite poles  Nuclear membrane and nucleolus disappear

Draw Prophase – use 2 colors Centrioles Doubled Chromosomes

Reproduction 3. METAPHASE – Middle Chromosomes line up down middle of cell

Draw Metaphase Spindle

Reproduction 4. ANAPHASE - Away  Chromosomes split at the centromere  Sister chromatids move away to opposite poles, so each side has an identical copy of each chromatid

Draw Anaphase

Reproduction 5. TELOPHASE – To normal  Chromatids begin to elongate and uncoil – go back to being in form of chromatin  Mitotic spindle disappears  Nuclear membrane forms around each set of chromosomes  Nucleolus reappears

Reproduction LASTLY…  CYTOKINESIS – cytoplasm divides  Results in 2 IDENTICAL daughter cells!

Draw Telophase/Cytokinesis

Reproduction Is Mitosis the same in plant cells???  The process is very similar, but there are 2 differences:

Reproduction 1. Plant cells do not have centrioles  a spindle does form and the chromosomes move in the same way as animal cells

Reproduction 2. Plant cells have rigid cell walls, so they do not pinch-in during telophase  a cell plate forms across the middle of the cell.  cell plate grows outward and joins old cell wall which divides the cell in half

Plant Cell Mitosis

Interphase of Cell Cycle Whitefish cells

Prophase

Metaphase

Anaphase

Telophase

Animal Cell Mitosis

Animations Tosis/mitosis-animation.gif Tosis/mitosis-animation.gif

Videos Mitosis and Meiosis = (mitosis = 1-17:28) Mitosis – Part 1 = 4:18 MitosisMeizisis = 27:33

What Causes Aging? Telomeres s/telomeres/ s/telomeres/ Progeria (2:28) night.html night.html Aging video on server – (9:06)

What is Cancer Cancer is uncontrolled cell division.

Applicable NY State Learning Standards 2.1d, 4.1b, 4.1c

How do Organisms Reproduce Asexually??? BY MITOSIS!!!

Define Asexual Reproduction: When a single parent cell produces identical offspring by dividing into 2 cells!

Types of Asexual Reproduction

Type: Binary Fission Examples: BACTERIA and other one-celled organisms. Description:  Cell goes through mitosis  Cytoplasm divides into 2 EQUAL parts.

Binary Fission

Type: Budding Examples: - yeast, hydra, and sponges. Description:  Cell goes through mitosis  Cytoplasm divides into 2 UNEQUAL parts.

Budding

Type: Sporulation Examples: fungi and ferns. Description:  Organisms produce large numbers (thousands) of spores by mitosis.  Spores are highly resistant cells that can mature into adult plants.

Sporulation

Type: Regeneration Examples: Starfish, earthworms, and planaria. Description:  Simple organisms can re-grow lost parts.  Parent cells near missing body parts go through mitosis.

Regeneration

Type: Vegetative Propagation Examples: See below. Description:  Asexual reproduction of plants using its roots, stems, or leaves.

Vegetative Propagation 1.Runners Example – strawberry plants! Description:  Stem that grows sideways and has buds!  New plant grows where runners touch ground.

Vegetative Propagation - Runners

Vegetative Propagation 2.Cuttings Example - ivy Description:  Piece of a root, stem, or leaf removed from a plant. Grow in water, then plant in soil.

Vegetative Propagation – Cuttings

Vegetative Propagation 3.Grafting Examples: oranges, grapes Description:  Cut branch from 1 tree is attached to the base of another.

Vegetative Propagation - Grafting

Unit 8: Part 2 Meiosis

Sexual Reproduction The offspring are NOT identical to either parent.  Accomplished through meiosis and fertilization Results in increased variation in species which increases the chance of survival.

Remember:  Mitosis occurs in all body cells (somatic), EXCEPT sex cells  Body cells contain a DIPLOID (2n) –the normal number of chromosomes.  We have 2 chromosomes of each type (1 from mom, 1 from dad)  For example, humans have 23 homologous pairs (total of 46) of chromosomes in body cells.

Human Karyotype We have 2 copies of each chromosome (1 from mom and 1 from dad)

Meiosis Part 2: Meiosis Organisms that reproduce SEXUALLY need to produce sex cells that have ½ the normal chromosome number.

Meiosis So, when an egg + sperm come together (fertilization) the original chromosome number is restored! += The process used to create these specialized sex cells is MEIOSIS!!! 1n 2n

Meiosis Define: Meiosis:  Formation of sex cells that contain 1 chromosome of each homologous pair (matching pairs)

Meiosis Result of Meiosis:  One cell results in the formation of 4 cells that have ½ the number of chromosomes.

Result of Meiosis:

Meiosis How does MEIOSIS work???  There are 2 divisions in meiosis:  Round 1 (when reduction occurs):

Meiosis  INTERPHASE is the same as in mitosis:  Chromatin doubles  Cell prepares for meiosis

Homologous Chromosomes

Meiosis  PROPHASE I:  The chromosomes become shorter and more coiled as in mitosis.  DIFFERENCE: The replicated chromosomes line up exactly with its homologous chromosome. NOTE: HOMOLOGOUS chromosomes are not identical – but they match very closely in terms of the genes they carry.

Meiosis DIFFERENCE:  The homologous pairs then become attached at their centromeres forming TETRADS – forming of the tetrads is called SYNAPSIS.

Meiosis DIFFERENCE:  When the tetrads are together, the chromosomes twist about each other and exchange parts or characteristics – called CROSSING OVER.  ***This results in genetic variability**

Crossing Over

Prophase I

Meiosis METAPHASE I:  The tetrads (homologous chromosomes and their copies) formed in prophase line up in the middle.  Centromeres of chromosomes attach to the spindle fibers

Metaphase I

Meiosis ANAPHASE I:  DISJUNCTION - The homologous chromosomes of each tetrad separate and move to opposite ends of the cell.  Each cell will receive only 1 chromosome from each homologous pair, but that chromosome still has its sister chromatid.

Anaphase I

Meiosis TELOPHASE I and CYTOKINESIS:  Same as in mitosis – cytoplasm divides and results in 2 daughter cells.  BUT – each cell has half as many chromosomes as the original cell, because each cell has only 1 chromosome from each homologous pair.

Telophase I and Cytokinesis

Meiosis So, now we have 2 cells that have half of the number of chromosomes as in the original cell, and each chromosome still has a sister chromatid.

Meiosis Round 2 (2 nd division – much like mitosis):  The 2 cells go right into prophase II (no doubling of chromosomes needed, so no interphase)

Meiosis PROPHASE II:  Each daughter cell forms a spindle and double-stranded chromosomes move toward middle. METAPHASE II:  Chromosomes attach to spindle fibers at their centromeres and line up in the middle.

Prophase IIMetaphase II

Meiosis ANAPHASE II:  The centromeres divide and the sister chromatids separate.  These single-stranded chromosomes move to opposite ends of the cells.

Anaphase II

Meiosis TELOPHASE and CYTOKINESIS II:  Both daughter cells divide.  Result is 4 MONOPLOID cells – the genetic material is different in each cell and they do not match the parent cell!  Now we have 4 cells with single-stranded chromosomes (1/2 the normal number).

Telophase II and Cytokinesis

Gametogenesis - Males

Gametogenesis-Females

Meiosis Animations/Videos On server: ‘Mitosis and Meiosis’- at 17:28-26:13