Cell Division: Asexual Reproduction

Interphase Mitosis Cytokinesis Asexual Binary Fission OUTCOME QUESTION(S): S1-1-02: Why do cells divide and how does it work? Vocabulary & Concepts  Interphase Mitosis Cytokinesis Asexual Binary Fission

Why do cells divide and how does it work? All “new” cells (growth, repair or reproduction) are produced from “old” cells – every cell is either dividing, or preparing to divide… Why do cells divide and how does it work?

Interphase Longest phase Living life and preparing for eventual division Chromosomes (46 books) must be copied

Mitosis is how all new somatic (body) cells are made Division phase - consists of two parts: 1. Mitosis - division of chromosomes and nucleus. Giving both cells a complete set of “books” Mitosis is how all new somatic (body) cells are made 2. Cytokinesis - dividing cytoplasm and organelles. End Result: Two identical cells that re-enter interphase begin the process again.

Chromosomes look like spaghetti - uncondensed There is obviously a lot more going on in the cell…but we are just focused on what the chromosomes are doing during interphase and mitosis Chromosomes look like spaghetti - uncondensed Chromosomes copied, cell grows and makes more organelles (preparing to divide)

Chromosomes become visible – condense Centrioles Sister Chromatids Chromosomes become visible – condense Copied chromosomes are joined – look like “X” If a chromosome has the “X”-shape – it is joined chromosome copies – called sister chromatids

Chromosomes are guided into the middle by attached spindle fibres Sister Chromatids Copied chromosomes (sister chromatids) line-up along the middle of the cell Chromosomes are guided into the middle by attached spindle fibres

Copied chromosomes (sister chromatids) pulled separated Copied chromosomes (sister chromatids) pulled apart towards opposite ends of cell This is done by the spindle fibres “shortening” and pulling them inwards

Chromosomes back to spaghetti - uncondensed Cleavage of cell into two Chromosomes back to spaghetti - uncondensed A new nucleus forms around each set of chromosomes

Leaving 2 identical daughter cells Cytokinesis Cell membrane grows inwards - pinching into 2 Each daughter cell has a complete set of the chromosomes – plus organelles and cytoplasm Leaving 2 identical daughter cells

Identical daughter cells Interphase Prophase Metaphase Parent cell Copied and condensed Lining up Anaphase Telophase Cytokinesis Pulling apart Nucleus forming Identical daughter cells MITOSIS

Full set of Chromosomes Full set of Chromosomes MITOSIS – in general P M A T Parent cell: Full set of Chromosomes This is the general structure that you will have to understand occurs for all 46 chromosomes Daughter cells: Full set of Chromosomes 2 identical daughter cells

Asexual and Sexual Why do cells divide? Reproduction – Pass on genetic information There are 2 types of organism reproduction: Asexual and Sexual

Create offspring from one parent organism Asexual Reproduction Create offspring from one parent organism Using basic cell division - Mitosis Rapid and effective reproduction method Cells are “clones” – genetically identical Mitosis IS asexual reproduction: making an identical copy (offspring) from an existing cell (parent)

Binary Fission One example of Asexual Reproduction: Simple single-cell (unicellular) organisms Bacteria have 1 circular chromosome (plasmid) Bacteria (like E. Coli) Remember: even though we call this “binary fission” it is still just a simplified Mitosis

Some other examples of Asexual Reproduction: Fungi (yeast) Bacteria Fungi (mould)

Full set of Chromosomes Full set of Chromosomes MITOSIS – in general P M A T Parent cell: Full set of Chromosomes Remember: ALL asexual methods of reproduction are just fancy Mitosis Daughter cells: Full set of Chromosomes 2 identical daughter cells

PROS – Asexual Reproduction – CONS No diversity in organisms clones are vulnerable to disease/environment Large number of offspring made very quickly Each offspring will be successful clones are well adapted Little possibility for evolution clones are identical Stay close together colonies build if nutrients are present Can lead to overcrowding starvation if not enough nutrients No need to waste energy finding a sexual partner ?

CAN YOU ANSWER THESE QUESTIONS? S1-1-02: Why do cells divide and how does it work? Vocabulary & Concepts  Interphase Mitosis Cytokinesis Asexual Binary Fission