Unit 5 Mitosis Meiosis Why do cells divide

Unit 5 Mitosis & Meiosis

Why do cells divide rather than grow bigger? – Have you ever been in a traffic jam in a small town? – Where are major traffic jams found? • As a city’s population grows, more people are moving in an out which causes traffic • Cells are like cities – The bigger they are, the more food, water, and

Why do cells divide rather than grow bigger? • To prevent traffic jams, they will divide Prevent divide the cell from too big (prevent traffic jam) • 1. Cells forbecoming 4 major reasons: 2. To heal injuries 3. To allow the organism to grow (up) 4. To reproduce (new individuals)

Before we get started with the cell cycle…. Lets talk about chromosomes Chromosome: DNA-containing structure that carries genetic material from one generation to another.

What happens during the cell cycle? Cell Cycle - Process of cellular reproduction, occurring in the main stages 1. Interphase (growth) 2. Mitosis (nuclear division) 3. Cytokinesis (cytoplasm division)

What occurs during Interphase (the 1 st step in cell cycle) • There are 3 stages during interphase: 1 st Grows 2 nd Duplicates DNA 46 Chromosomes 3 rd Prepares to divide 92 Chromosomes

Clicker Question #1 Which of the following is NOT a reason cells divide? a. To heal injuries b. To allow the organism to grow c. To reproduce d. To maintain homeostasis

Clicker Question #2 What will happen if the cell continued to grow rather than divide? a. b. c. d. The organism would get too big Food & wastes would not be able to move in & out as easily The surface area would increase and allow more materials into and out of the cell Nothing would happen

Clicker Question #3 What are the 3 stages of the cell cycle? a. b. c. d. Prophase, Metaphase, & Anaphase Mitosis, Telophase, & Cytokinesis Interphase, Metaphase, & Prophase Interphase, Mitosis, & Cytokinesis

Clicker Question #4 Which of the following is NOT a stage during interphase? a. b. c. d. Growth (G 1) DNA replicates (S) Prepares to divide (G 2) Mitosis (M)

What is Mitosis? Mitosis: 2 nd main stage of the cell cycle during which the cell’s replicated DNA divides and 2 genetically identical diploid daughter cells are produced.

What occurs during mitosis? (the 2 nd step in cell cycle) • There are 4 stages during mitosis: 1 st Prophase (pro = 1 st) 2 nd Metaphase 3 rd Anaphase 4 th Telophase (telo = end)

What occurs during mitosis? (the 2 nd step in cell cycle) • There are 4 stages during mitosis: 1 st Prophase (pro = 1 st) Nucleus disappears Centrioles separate

What occurs during mitosis? (the 2 nd step in cell cycle) • There are 4 stages during mitosis: 2 nd Metaphase Chromosomes line up in the middle

What occurs during mitosis? (the 2 nd step in cell cycle) • There are 4 stages during mitosis: 3 rd Anaphase Chromosomes move apart

What occurs during mitosis? (the 2 nd step in cell cycle) • There are 4 stages during mitosis: 4 th Telophase (telo = end) Nucleus reappears Cytoplasm starts to separate

What occurs during cytokinesis? (the 3 rd step (LAST) in cell cycle) • Cytokinesis: The last stage of the cell cycle, during which the cell’s cytoplasm divides, creating a new cell. Daughter Cells

Clicker Question #5 Mitosis creates: a. 4 genetically identical cells b. 2 genetically identical cells c. 4 genetically different cells d. 2 genetically different cells

Clicker Question #6 What are the 4 stages of mitosis in order? a. Interphase, prophase, metaphase, anaphase b. Interphase, prophase, metaphase, telophase c. Prophase, metaphase, telophase, cytokinesis d. Prophase, metaphase, anaphase, telophase

Clicker Question #7 This is the last phase of the cell cycle where the cell’s cytoplasm divides to create 2 daughter cells: a. Cytokinesis b. Interphase c. Telophase d. Metaphase

Now, lets look at the difference between gametes & body cells.

What is the difference between gametes & body cells? Gametes – A haploid sex cell, formed during meiosis, that can combine with another haploid sex cell and produce a diploid fertilized egg. Sperm & Egg are gametes! How many chromosomes are in human gametes? 23

What is the difference between gametes & body cells? What are “bodyancells”? Does. Brain more chromosomes organism has cells Eye cells Everything EXCEPT mean Heartthat cells it is more Tongueadvanced/smarter? cells GAMETES! Skin cells Muscle cells Blood cells Lung cells Kidney cells Nerve cells How many chromosomes do we have in No …example: each of our body cells (not sex cells)? King Crabs have 208 chromosomes in each cell Turkeys have 82 chromosomes in each cell Humans have in our body cells 46

Body cells reproduce using mitosis. Start with 1 diploid Notice that they are IDENTICAL! End with 2 diploid

What is the difference between diploid and haploid? Diploid – Having two copies of each chromosomes (2 n) Body cells are Diploid If you see Diploid… Skunks Humans have 50468 Fruit flies have You think DOUBLE!

Diploid Video

What is the difference between diploid and haploid? Haploid – Cell with half the number of chromosomes (n) 23 23 23 Gametes are Haploid 23 If you see haploid… Humans have 23 Skunks have 25(in 4(insexsex(incells) Fruit flies have sex cells) You think HALF! Remember: have 46 in (in cells) Remember: Humans Skunks have 50 cells Remember: Fruit Flies have 8 body inbody cells

Haploid Video

Clicker Question #8 Sperm and eggs are: a. gametes b. somatic cells c. body cells d. all of the above

Clicker Question #9 How many chromosomes are in human gametes? a. b. c. d. 36 23 20 15

Clicker Question #10 Which of the following is an example of a haploid cell? a. b. c. d. brain cell skin cell heart cell sperm cell

Clicker Question #11 Mitosis results in: a. b. c. d. 2 diploid cells 2 haploid cells 4 diploid cells 4 haploid cells

Gametes are formed using meiosis Starts with 1 diploid Notice that they are NOT IDENTICAL Ends with 4 DIFFERENT haploid

What happens during Meiosis? Meiosis: Reduction division process, occurring only in reproductive cells, in which 1 diploid (2 n) cells produce 4 haploid (n) cells that are NOT genetically identical. Creates SPERM inside the testes of males Creates EGGS inside the ovaries of females

What happens during Meiosis? There are 2 stages during Meiosis: Meiosis I & Meiosis II Meiosis I is exactly like mitosis EXCEPT that Crossing-over occurs during prophase I

What happens during Meiosis? Crossing-over: Exchange of chromosomal segments between a pair of homologous chromosomes during prophase I of meiosis Meiosis II

Why is crossing-over so important? (cuz it is) • It creates genetic variation! • Even though you look similar to your siblings (if same parents), there will never be another person exactly like you because of crossing-over…your parents could have a million kids, and not one of them will look exactly like you! (except for identical twins, but even they have some differences) Genetic variation allows some individuals to: * Run faster than you * Fix things better than you * Solve math problems better than you * Train animals better than you * Fly airplanes better than you * Swim better than you * “Look better” than you * Paint better than you * Sing better than you * Farm better than you * Dance better than you * Jump better than you

Crossing-Over Continued… Crossing-over occurs between homologous chromosomes. Homo means ___? The same crossing-over patterns do SAME not occur…they create all different kinds of they combinations…often Homologous Chromosomes means that contain the SAME Being genetically unique called “recombination”…this genes, in the SAME order as each other, but the message in the creates genetic diversity! makes usthe genetically unique. genes may be slightly different between two. …diversity GOOOOD! - Soisyour mom’s code could be for blue eyes Genetic diversity allows some And yourspecies dad’stocode individuals- of the same continue as their environment changes…even if others can’t survive. could be for brown

Hypothetical…. lets say you are a duck… And shaking your tail feathers will Then this is the duck that help you find a mate… will pass on his genes! cuz that is what the ladyz are look’n for

Hypothetical…lets say you are a caveman Which of these would be LESS likely to survive? Because all these cave people have genetic diversity, but one lacks an important trait (ability to build tools), he will not survive his environment… but the others will!

What happens during Meiosis? Next is Meiosis II…. * The division process happens again…BUT Meiosis I The DNA does NOT copy before dividing Meiosis II & No crossing-over Results in 4 haploid cells that are NOT identical

Clicker Question #12 Which of the following cells are formed during meiosis? a. b. c. d. skin cells liver cells egg cells kidney cells

Clicker Question #13 Which of the following cells are formed during mitosis? a. b. c. d. skin cells sperm cells egg cells all of the above

Clicker Question #14 Meiosis results in: a. b. c. d. 2 identical haploid cells 4 different haploid cells 2 different haploid cells

Clicker Question #15 This allows some individuals of the same species to continue as their environment change even if others can’t survive a. b. c. d. identical twins cloning genetic variation biodiversity

Clicker Question #16 The exchange of chromosomal segments during meiosis is called: a. b. c. d. interphase crossing-over transcription exchanging-over

Clicker Question #17 Which of the following allows for genetic diversity? a. b. c. d. meiosis mitosis homeostasis all of the above

Houston…We have a problem… Non-disjunction: Cell division in which the sister chromatids do NOT separate correctly, resulting in gametes with an abnormal number of chromosomes. This is how Down Syndrome These are correct! happens…the chromosomes don’t Noticeand there are separate correctly, too many No problem end up in chromosomes the gamete. NO in Notice thesethat cells! People with Down Syndrome have non-disjunction occurred 47 chromosomes instead of ____. 46 here too!

Click on Link for animation… Meiosis Overview

Page 35 in Comp Book Compare & Contrast Mitosis & Meiosis Mitosis * Occurs in body cells * Divides once * Creates 2 cells * Are genetically identical Meiosis Both * Creation of new cells * Occurs in gametes cells * Divides twice (meiosis 1 & II * Creates 4 cells * DNA replicates once * Are NOT genetically identical * Increases genetic diversity

Clicker Question #18 This results in gametes with abnormal numbers of chromosomes: a. b. c. d. meiosis mitosis non-disjunction crossing-over

Clicker Question #19 This is an example of nondisjunction: a. b. c. d. Color blindness Down Syndrome Cystic fibrosis Sickle cell anemia

Many Bacteria & protozoans do not need a partner to reproduce. Are they reproducing using mitosis? Answer: NO. . . They are using Binary Fission – Asexual form of reproduction used by some prokaryotes in which a cell divides into two genetically identical cells. (creates a new individual) SIMILAR/LIKE “cloning” themselves 1 bacterium could become 1, 000, 000 (billion) in 10 hours!

What are the advantages & disadvantages to being asexual & sexual? Asexual Reproduction Advantages Disadvantages Can reproduce without a partner… No genetic variation…They are clones. Its putting all your eggs in one basket. If a something kills the parent, it WILL kill ALL the offspring too. Easily becomes extinct with little change to environment. They don’t have to find a mate/partner. Able to reproduce quickly. The greater the number of offspring, the better the survival rate of the population. Quick reproduction is also a disadvantage because too many individuals will be competing with each other food & space

What are the advantages & disadvantages to being asexual & sexual? Sexual Reproduction Advantages Disadvantages Genetic diversity! Has the ability to create endless recombination of genes (crossing-over) coming from 2 parents, all individuals are different in some way. Must find a partner. Very difficult if the population is low and spread out. Difficult to recover if the species is endangered. The species is more able to adapt to environmental changes Slow reproduction…. takes time… Slow population growth

Clicker Question #20 Prokaryotes reproduce using: a. b. c. d. meiosis mitosis binary fission binary fusion

Clicker Question #21 Which of the following is an advantage of asexual reproduction a. b. c. d. genetic diversity the ability to reproduce quickly the ability to adapt to new habitats slow reproduction

Clicker Question #22 Which of the following is an advantage of sexual reproduction a. b. c. d. genetic diversity the ability to reproduce quickly the ability to reproduce many offspring do not have to find a sexual partner

The End