1. Asexual Reproduction Mitosis The Cell Cycle With an introduction to: &

2. Asexual Reproduction What is Asexual Reproduction? All living things need to reproduce themselves to continue their species; they do this sexually, asexually, or use a combination of both Asexual reproduction is the opposite of sexual reproduction in that it does not involve the fusion of both male and female gametes (sex cells) Asexual reproduction means (1) that an individual, or part of an individual can produce an offspring that has identical genetic makeup to itself, or (2) grow or regenerate new tissue that also is genetically identical An identical offspring is known as a clone. Uses a process called Mitosis to produce new cells

3. Asexual Reproduction AdvantagesDisadvantages Organism doesn’t need to invest time and energy in a partner Organism doesn’t have to travel to propagate its species Less chance of harmful genetic mutation Less chance of anything going wrong as it is a simpler process Maintains desirable traits Organisms can reproduce faster In comparison to sexual reproduction…. No opportunity for genetic variation by mixing of genes Little genetic change within a species gene pool means little chance of species improvement and evolution Lack of genetic change is particularly harmful to species when environmental conditions change and the organism can’t adapt

4. Asexual Reproduction Types of asexual reproduction are: Budding Fission Spore formation Fragmentation Vegetative reproduction Parthenogenesis

5. Asexual Reproduction Budding This occurs when a new organism is formed from an outgrowth from the original parent When the outgrowth is large enough it frees itself from the parent Examples include; yeast cells and some types of worms Yeast cell in the process of budding Budding scar

6. Asexual Reproduction Binary Fission Occurs in bacteria and some protista The cell duplicates its DNA and then extends its cell membrane from the centre The cell elongates from the centre in each direction until it is long enough to cleave This is a very fast method of reproduction with the population of a colony sometimes doubling every 15-20 minutes.

7. Asexual Reproduction Binary Fission Imagine this one bacteria doubling every 15 minutes How long will it take to fill this rectangle?

8. Asexual Reproduction Spore Formation Spores are single cells produced by an organism and released into the environment to propagate Organisms that produce spores include prokaryotes, protists, fungi and plants such as ferns and mosses A cloud of spores being released

9. Asexual Reproduction Fragmentation Takes place in plants and animals Occurs when the organism breaks into 2 or more pieces A whole new organism is produced from each piece Examples include; sponges and some types of worms

10. Asexual Reproduction Vegetative Reproduction Happens only in plants Occurs when a new plant is produced from part of another plant Examples include: grafts – used commercially to produce desirable traits in flowers and fruit trees bulbs – such a daffodils, garlic tubers – such as potatoes; new plants can grow from the tuber runners – such as strawberries; new roots grow from a runner to make a new plant

11. Asexual Reproduction Parthenogenisis When an individual is produced from an unfertilized egg, therefore known as the virgin birth Mostly occurs in invertebrates Examples includes bees; the queen lays eggs that will produce females if fertilized and males, or drones, if not fertilized

12. Asexual Reproduction Before we can understand how organisms actually reproduce themselves asexually at a cellular level, we need a little background knowledge: (1) We need to understand the regular cycles that cells make within their life cycle – This is known as the cell cycle (2) We need to have a look at the actual process of nuclear division – This is called mitosis Some background information…………..

13. 1. The Cell Cycle Most cells replicate themselves over and over. Each complete replication is known as the cell cycle The length of time the cell cycle takes depends on the type of cell, but it can vary from hours to days The best way to study the cell cycle is to think of it as a 24hr clock Start Finish There are 2 main stages……

14. 1. The Cell Cycle InterphaseMitosis The cell cycle can be divided into 2 main parts Interphase and Mitosis Interphase can be divided into 3 main sections; G1, S phase and G2 G1 S Phase G2 Let’s have a closer look at what happens during the Interphase part of the cell cycle……..

15. 1. The Cell Cycle In G1 – or Gap 1 – the cell grows in size. Chromosome number is haploid, written as 1N In S Phases – or synthesis phase – the DNA in the nucleus replicates or duplicates itself and becomes diploid, written as 2N In G2 – or Gap 2 – the cell gets ready for cell division

16. 1. The Cell Cycle InterphaseMitosis The Mitosis section of the cell cycle can also be divided up into a few sections, this time into 4 sections ……………

17. 1. The Cell Cycle Prophase Metaphase Anaphase Telophase Mitosis: Nuclear division A mnemonic is useful in remembering the order of the stages of mitosis. If you can’t think of your own try: (He) probably met Ana (at the) telethon! Cytokinesis: Division of the cytoplasm

18. 2. Mitosis Mitosis is the division of the genetic material in the nucleus of the cell Each parent cell gives rise, or produces, two identical daughter cells Mitosis has 4 major stages: prophase, metaphase, anaphase and telophase When the nucleus in a cell is not undergoing mitosis it is said to be in interphase Mitosis occurs in all the somatic cells (or body cells) and not in the gametes (or sex cells) in humans

19. 2. Mitosis cell membrane nuclear membrane nucleolus A simplified cell nucleus Mitosis occurs in the nucleus of cells centrioles

20. 2. Mitosis Interphase Cell membrane Nuclear membrane DNA The cell has replicated its DNA in S Phase and is now in G2 Phase preparing for Mitosis The DNA condenses by folding on itself even more than usual You can start to see the chromosomes, they look like spaghetti on a plate!

21. 2. Mitosis Early prophase The 6 chromosomes in this nucleus have been colour coded in their homologous pairs so we can follow them in this display; 2xblue, 2xgreen and 2xred The coloured pairs are also called homologous chromosomes; one shade is from mum and one shade is from dad one blue chromosome from mum one blue chromosome from dad

22. 2. Mitosis Prophase The chromosomes have condensed as much as they can; they now look like the letter ‘H’. The two vertical arms of the chromosome are called sister chromatids and they are connected by a centromere The centrioles duplicate themselves centromere sister chromatids from mum from dad Homologous chromosomes

23. 2. Mitosis Prophase The chromosomes start to line up on the metaphases plate that runs down the centre of the cell The centrioles start to move in opposite directions The nuclear membrane begins to break down metaphase plate

24. 2. Mitosis Late Prophase Centrioles continue to move to opposite ends of the cell Nuclear membrane breaks down even more

25. 2. Mitosis Late Prophase Centrioles arrive at opposite ends of the cell Nuclear membrane has completely broken down

26. 2. Mitosis Metaphase Chromosomes are lined up on the metaphase plate Centrioles build spindle fibres Centromeres join to spindle fibres Spindle fibres

27. 2. Mitosis Anaphase Chromosomes are pulled apart and sister chromatids move to opposite ends of the cell along the spindle fibres

28. 2. Mitosis Anaphase Sister chromatids continue to pull part Cell membrane starts to pinch or cleave cleavage

29. 2. Mitosis Telophase Cleavage continues and a cell plate is formed in plants cells only(this becomes the cell wall) New nuclear membranes form around the new nuclei Two daughter cells are now evident cell plate forms in plant cells

30. 2. Mitosis Telophase Chromosomes start to de- condense Nuclear membranes properly formed

31. 2. Mitosis Interphase The nucleolus returns Chromosomes are no longer visible Two new daughter cells identical to their parent

32. 2. Mitosis So nuclear division, or Mitosis starts from an interphase cell coming out of G2 and finishes as an interphase cell ready for G1. Let’s have a look again at the process of Mitosis, this time we won’t stop…………..(click as fast as you like to work the animation!)………..

33. Mitosis

46. The end