Unit 7: Cellular Reproduction 200 Ch. 22: Cell Reproduction 22:1 Mitosis & 22:2 Meiosis Body (somatic) cells divide Formation of sex cells (gametes) Diploid = 2n 2n haploid = n n Meiosis 1 Meiosis 2 Diploid (2N)  cells having 2 of each chromosome (n = the # of different chromosomes… ex humans have 23 different pairs, so 2N = 46 chromosomes) Haploid (N)  having 1 of each homologous chromosomes)

Recall… Why are cells small? How do cells “stay” small? to keep surface area to volume ratio high How do cells “stay” small? by dividing What must happen before a cell divides? Why? DNA is replicated so each new cell gets a copy Why else do cells divide? growth (increase # of cells) repair damage replace old/worn out cells Why are cells small? To keep SA : Vol high so materials can diffuse efficiently How do cells “stay” small? Stay small by dividing (mitosis) What must happen before a cell divides? DNA must replicate Why? So that once the cell divides, each new cell gets an exact copy of the DNA Aside from keeping cells small, why do cells divide? To increase the # of cells in an organism so that it can grow; to repair damaged cells; to replace old/worn out cells Remember… all cells come from preexisting cells (part of cell theory)

Cell Reproduction in Prokaryotes Prokaryotes have a single, circular chromosome. Cell reproduction is by binary fission. chromosome duplicates & cell divides in ½. Each daughter cell is genetically identical to each other as well as parent cell. Single chromosome attaches to cell membrane duplicate chromosome is formed, also attaches to membrane new cell membrane & wall grows between attachment sites separates 2 chromosomes forming 2 new daughter cells each w/ a copy of the chromosome

What are the 2 Types of Cellular Reproduction in Eukaryotes? mitosis meiosis occurs in all body (somatic) cells cell divides once results in: 2 diploid cells with same # of chromosomes (as parent cell) 46 (23 pairs) (humans) function: growth repair occurs in (germ) cells of reproductive organs ovaries & testes cell divides twice results in: 4 haploid cells with ½ # of chromosomes (as parent cell) 23 (humans) function: makes gametes (sperm & eggs) for sex. reprod. promotes variation Mitosis is like photocopying a cell…. It makes an identical copy of the cell…. Maintains genetic continuity (daughter cells are identical to parent cell & to each other) Meiosis promotes variation b/c combination of DNA from each parent (as well as crossing over and independent assortment when each gamete was formed)

Diploid & Haploid Cells What does it mean when a cell is “diploid”? cell contains two of each (type of) chromosome & thus 2 sets of genes 1 from each parent How do we indicate that a cell is “diploid”? represented by 2n ex. humans  2n = 46 What types of cells are “diploid”? ex. somatic (body) cells Same type of chromosome = homologous chromosome Diploid (2N)  cells having 2 sets of each chromosome… one set from each parent (n = the # of different chromosomes… ex humans have 23 different chromosomes… in pairs… one half of the pair is from each parent, so 2N = 46 chromosomes) In body (somatic) cells Haploid (N)  having 1 of each (homologous) chromosome… half the number of diploid cells Haploid first seen in telophase 1 of meiosis In gametes (Egg & sperm or sex cells)

Diploid & Haploid Cells What does it mean when a cell is “haploid”? cell contains one of each (type of) chromosome & thus 1 set of genes ½ the original number How do we indicate that a cell is “haploid”? represented by n ex. humans  n = 23 What types of cells are “haploid”? ex. gametes (sperm/eggs) Same type of chromosome = homologous chromosome Diploid (2N)  cells having 2 sets of each chromosome… one set from each parent (n = the # of different chromosomes… ex humans have 23 different chromosomes… in pairs… one half of the pair is from each parent, so 2N = 46 chromosomes) In body (somatic) cells Haploid (N)  having 1 of each (homologous) chromosome… half the number of diploid cells Haploid first seen in telophase 1 of meiosis In gametes (Egg & sperm or sex cells)

Cellular Reproduction: Mitosis & Meiosis body (somatic) cells divide formation of sex cells (gametes) diploid 2n = 4 (double stranded) haploid n = 2 2n = 4 (single stranded) Meiosis 1 Meiosis 2 n = 2 (double stranded) 2n = 4 (double stranded) Diploid (2N)  cells having 2 of each chromosome (n = the # of different chromosomes… ex humans have 23 different pairs, so 2N = 46 chromosomes) Haploid (N)  having 1 of each homologous chromosomes) Haploid cells can’t be produced by mitosis, instead they are produced by meiosis Diploid cells contain two complete sets (2n) of chromosomes Examples: Skin, blood, muscle cells Cell Division and Growth: Diploid cells reproduce by mitosis making daughter cells that are exact replicas… maintaining genetic continuity Haploid cells have half the number of chromosomes (n) as diploid - i.e. a haploid cell contains only one complete set of chromosomes Examples: Cells used in sexual reproduction (Sperm and ova) Cell Division and Growth: Haploid cells are a result of the process of meiosis, a type of cell division in which diploid cells divide to give rise to haploid germ cells. A haploid cell will merge with another haploid cell at fertilization… promoting genetic diversity n = 2 (double stranded) (single stranded) 2n = 4 (single stranded) n = 2 n = 2 n = 2

Mitosis (Ch. 22:1)

The Cell Cycle Has 3 Main Phases Interphase Mitosis has 4 parts Prophase Metaphase Anaphase Telophase Cytokinesis I Pee MATt, C? cytokinesis C During the cell cycle, a cell grows, prepares for division, & divides to form 2 identical daughter cells… each of which then begins the cycle again… Cell cycle seems to be regulated, at least partially, by cell-to-cell contact Interphase is the longest phase of the cell cycle (not part of mitosis… before mitosis) Cytokinesis (not part of mitosis… after mitosis… although often “grouped” together with the telophase stage of mitosis) Different cells can be at different stages at the same time… Another way to remember…. I play matches at the court…. Which takes longer, interphase or mitosis?

A. Before Mitosis: Interphase What is happening in the cell? life functions are being carried out DNA is in the form of...? chromatin What happens before mitosis begins? DNA replicates forming 2 strands called sister chromatids held together by centromere centrioles duplicate (in animal cells only) Interphase is the longest phase of the cell cycle Non-reproducing stage Cell is carrying out life functions, making new cell parts, growing, making RNA, making proteins When a cell is not preparing to divide DNA is relaxed in the form of chromatin (loose spaghetti-like form) When a cell is preparing to divide it forms into chromosomes. (coiled “X”) Sister chromatids are two identical copies of a single chromosome that are connected by a centromere (“snap”) (Think of a centromere like a snap holding the two sister chromatids together.)

B. Mitosis (Prophase—Step 1) Spindle fibers centrioles centrioles centrioles centrioles centrioles centrioles centrioles centrioles What happens during prophase? Double-stranded chromosomes become clearly visible. Nucleolus & nuclear membrane disintegrate. (In animals) centrioles move to opposite poles (ends). Spindle fibers form connecting centrioles. Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Chromosomes now look like Xs (DNA in condensed form) In plants: No centrioles, but have spindles

B. Mitosis (Metaphase—Step 2) What happens during metaphase? Chromosomes line up at middle (equator) of cell. Chromosomes attach to spindle fibers by centromeres. Meta  middle

B. Mitosis (Anaphase—Step 3) What happens during anaphase? Centromeres divide. Sister chromatids are pulled apart (@ centromere) forming single-stranded chromosomes Chromosomes move toward opposite poles (away from middle). Think of this as the 2 sister chromatids unsnapping & pulling away from one another. Ana  away

B. Mitosis (Telophase—Step 4) What happens during telophase? Chromosomes gather at opposite ends of “cells”. Nuclear membrane reforms forming 2 new nuclei Chromosomes unravel back into chromatin form. Nucleoli reappear Cytokinesis begins cleavage furrow forms (animal) cell plate forms (plant) Mitosis is now complete, but cell division is not done yet… Telo  far

C. After Mitosis: Cytokinesis When does cytokinesis start? during telophase (but cytokinesis is not a phase of mitosis) What happens during cytokinesis? Cytoplasm is divided by cleavage furrow in animal cells by cell plate in plant cells which becomes new cell wall 2 new diploid cells are formed & have 2 of each chromosome Animal cell cytokinesis occurs by a process called cleavage. As seen in the diagram below, a cleavage furrow, appears. This furrow becomes deeper until, eventually, it breaks the 2 halves apart to form 2 daughter cells. In plant cells, a cell plate forms. 2 new cell walls develop along the middle lamella. The cells then break apart forming 2 daughter cells.

So, What is the End Result of Mitosis? The DNA that was duplicated during interphase is equally divided into 2 new diploid daughter cells same DNA as parent cell & each other 2 new diploid daughter cells with exactly the same DNA as parent cell… maintains genetic continuity

What stage of the cell cycle is represented by each number? 1 2 3 4 5 What stage of the cell cycle is represented by each number? 1 = Anaphase 2 = Prophase 3 = Telophase/cytokinesis 4 = metaphase 5 = interphase Mitosis Animations http://www.sumanasinc.com/webcontent/animations/content/mitosis.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf http://www.teachersdomain.org/asset/tdc02_vid_dnadivide/

Interphase Cytokinesis Cytoplasm divides forming 2 daughter cells that are identical to the parent cell & each other

What are the 2 Types of Cellular Reproduction in Eukaryotes? mitosis meiosis occurs in all body (somatic) cells cell divides once results in: 2 diploid cells with same # of chromosomes (as parent cell) 46 (23 pairs) (humans) function: growth repair occurs in (germ) cells of reproductive organs ovaries & testes cell divides twice results in: 4 haploid cells with ½ # of chromosomes (as parent cell) 23 (humans) function: makes gametes (sperm & eggs) for sex. reprod. promotes variation Mitosis is like photocopying a cell…. It makes an identical copy of the cell…. Maintains genetic continuity (daughter cells are identical to parent cell & to each other) Meiosis promotes variation b/c combination of DNA from each parent (as well as crossing over and independent assortment when each gamete was formed)

Cellular Reproduction: Mitosis & Meiosis body (somatic) cells divide formation of sex cells (gametes) diploid 2n = 4 (double stranded) haploid n = 2 2n = 4 (single stranded) Meiosis 1 Meiosis 2 n = 2 (double stranded) 2n = 4 (double stranded) Diploid (2N)  cells having 2 of each chromosome (n = the # of different chromosomes… ex humans have 23 different pairs, so 2N = 46 chromosomes) Haploid (N)  having 1 of each homologous chromosomes) Haploid cells can’t be produced by mitosis, instead they are produced by meiosis In plants & some algae & fungi meiosis results in haploid spores (small reproductive cells that can develop into new haploid organisms) Diploid cells contain two complete sets (2n) of chromosomes Examples: Skin, blood, muscle cells Cell Division and Growth: Diploid cells reproduce my mitosis making daughter cells that are exact replicas. Haploid cells have half the number of chromosomes (n) as diploid - i.e. a haploid cell contains only one complete set of chromosomes Examples: Cells used in sexual reproduction (Sperm and ova) Cell Division and Growth: Haploid cells are a result of the process of meiosis, a type of cell division in which diploid cells divide to give rise to haploid germ cells. A haploid cell will merge with another haploid cell at fertilization. n = 2 (double stranded) (single stranded) 2n = 4 (single stranded) n = 2 n = 2 n = 2

Meiosis: The Production of Gametes (22:2) What would happen if the # of chromosomes wasn’t reduced by ½ during meiosis? After fertilization there would be 2x the # of chromosomes How does meiosis promote genetic variation? “mixing” DNA from 2 different parents Through meiosis, the chromosome # is reduced to ½ the diploid (2n) #, resulting in the n or haploid # 2n = diploid n = haploid gametes only occurs in certain reproductive tissues (Meiosis occurs in my “O”s… ovaries… or testes if male…) results in 4 haploid cells that are genetically different from each other & the parent…. What if the # of chromosomes wasn’t reduced? Offspring would have 2x as many chromosomes…. So sperm must have ½ & egg must have ½ so that fertilization restores the diploid # in the newly formed zygote How is the reduction of chromosome # achieved??? Meiosis is a process of reduction division During meiosis 1 (in a diploid cell) double-stranded homologous chromosomes (tetrads) are separated… Resulting in 2 haploid cells (w/ one double-stranded copy of each chromosome)… this is the “reduction” During meiosis 2, sister chromatids are separated so, each cell has one (single-stranded) copy of each chromosome

Meiosis Interphase Meiosis 1 (separation of homologous chromosomes) has 4 parts Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Cytokinesis 1 Meiosis 2 (separation of sister chromatids… essentially mitosis) has 4 parts Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis 2 Let's look at meiosis -- consists of two nuclear division (meiosis I and II) -- in the first division, the chromosome number is reduced by 1/2 (diploid to haploid) -- the second division is actually nothing more than mitosis. End result of meiosis is 4 haploid daughter cells. Prior to meiosis, mother cells are in interphase -- like mitosis, DNA replication occurs during interphase just prior to meiosis. Meiosis I: the reduction division -- diploid mother cell produces 2 haploid cells. Meiosis II: mitotic division of 2 haploid cells to produce 4 haploid daughter cells. In sexually reproducing organisms, chromosomes exist as homologous pairs -- each chromosome has a "mate" or homologue that carries the same kind of genetic information -- one member of the homologous pair is maternally inherited and the other is paternally inherited -- e.g. humans have a diploid number of 46 chromosomes arranged as 23 homologous pairs.

traits. Different versions of a gene for the same trait are called “alleles”. In sexually reproducing organisms, chromosomes exist as homologous pairs -- each chromosome has a "mate" or homologue that carries the same kind of genetic information -- one member of the homologous pair is maternally inherited and the other is paternally inherited -- e.g. humans have a diploid number of 46 chromosomes arranged as 23 homologous pairs. Each chromosome of a pair has the same basic structure… the 2 members of each pair are called homologous chromosomes or homologues (carried information for same trait, although specific information may differ… ex both carry instructions for eye color, one may be for brown, one for blue)

A. Before Meiosis: Interphase What happens during interphase? Cell is diploid (has 2 of each chromosome) DNA replicates forming double-stranded chromosomes. But, the cell is still diploid (2n). Left picture 2n = 2 right picture 2n = 4

B. Meiosis 1 (Prophase 1—Step 1) What happens during prophase 1? Nucleolus & nuclear membrane disintegrates. (In animals) centrioles move to opposite poles. Spindle fibers form, connecting centrioles. Homologous chromosomes join (synapsis), forming tetrads (4 chromatids). genes may swap (crossing over) 2n During the first stage of meiosis, an unusual - and vitally important - event occurs: Crossing Over. During Prophase of Meiosis I, homologous chromosomes in the cell Pair up alongside each other lengthwise, and Swap bits and pieces of their chromosomes, shuffling the genome! Crossing Over ONLY happens in Prophase of Meiosis I, and results in NEW Chromosomes that did not exist before in the parent. crossing over Allows for more variation in offspring b/c produces new combination of alleles (gene variations) 2n = 4 in pics on left & right… pic in center 2n =2

B. Meiosis 1 (Metaphase 1—Step 2) What happens during metaphase 1? Spindle fibers attach to chromosomes. Tetrads line up (double file) @ the middle (equator). Can have different arrangements (due to independent assortment). What does this cause? genetic variability 2n Each side of equator can have chromosomes from either parent 2n = 4

B. Meiosis 1 (Anaphase 1—Step 3) What happens during anaphase 1? Tetrads (pairs of double-stranded homologous chromosomes) separate. move towards opposite poles 2n = 4 2n

B. Meiosis 1 (Telophase 1—Step 4) What happens during telophase 1? Chromosomes gather at opposite ends. Nuclear membrane reforms around each cluster of chromosomes forming 2 new haploid (n) nuclei with 1 of each double-stranded chromosome. Chromosomes unravel back into chromatin form. Nucleoli reappear. Cytokinesis 1 starts. n Cell finally becomes haploid (during telophase 1) N = 2 (even though chromosomes are double-stranded) n

C. After Meiosis 1: Cytokinesis 1 When does cytokinesis 1 start? during telophase 1 (but is not a phase of meiosis) What happens during cytokinesis 1? Cytoplasm is divided by cleavage furrow in animal cells. by cell plate in plant cells which becomes new cell wall. 2 new haploid cells are formed with 1 of each chromosome. N = 2 (even though chromosomes are double-stranded)

Moving From Meiosis 1 to Meiosis 2… Replication does NOT occur again before meiosis 2. Daughter cells from meiosis 1 stay haploid. Meiosis 2 happens in both daughter cells. Each cell is haploid w/ each chromosome being made of 2 sister chromatids Meiosis 2 Sister chromatids are separated (essentially by mitosis) n = 2

D. Meiosis 2 (Prophase 2—Step 1) What happens during prophase 2? Nucleolus & nuclear membrane disintegrate. (In animals) centrioles move to opposite poles. Spindle fibers form, connecting centrioles. n Each cell is haploid w/ each chromosome being made of 2 sister chromatids Meiosis 2 Sister chromatids are separated (essentially by mitosis) n = 2 n

D. Meiosis 2 (Metaphase 2—Step 2) What happens during metaphase 2? Spindle fibers attach to chromosomes at centromere. Double-stranded chromosomes line up (single file) @ equator so 1 sister chromatid is on each side of equator. n n n Left pic 2n = 4 n = 2 right pic n = 2

D. Meiosis 2 (Anaphase 2—Step 3) What happens during anaphase 2? Sister chromatids separate (at centromere) forming single-stranded chromosomes. move towards opposite poles n Meiosis 2 Sister chromatids are separated (essentially by mitosis) Right pic N = 2 Left pic n = 4 n

D. Meiosis 2 (Telophase 2—Step 4) What happens during telophase 2? Chromosomes gather at opposite ends. Nuclear membrane reforms around each cluster of chromosomes forming 4 new haploid (n) nuclei with 1 of each single-stranded chromosome. Chromosomes unravel back into chromatin form. Nucleoli reappear. Cytokinesis 2 starts. Forms 4 new “daughter” cells Haploid (n = 2 in this example) w/ ½ the # of chromosomes as original cell (4 chromosomes in this example) Chromosomes are individual (single) strands N = 2

E. After Meiosis 2: Cytokinesis 2 When does cytokinesis 2 start? During telophase 2 What happens during cytokinesis 2? cytoplasm is divided by cleavage furrow in animal cells. by cell plate in plant cells which becomes new cell wall. What does each new cell end up with? combo of chromosomes from mom & dad Only one chromosome from each homologous pair n n n Meiosis 2 Sister chromatids are separated (essentially by mitosis) N = 2 n

To summarize… Meiosis Has 2 Stages (Divisions)… Meiosis 1 Meiosis 2 Homologous chromosomes are separated, but are still double stranded. Cells become haploid. Meiosis 2 Sister chromatids are separated. Still haploid, but now have single strands. Meiosis 1 Homologous chromosomes are separated Meiosis 2 Sister chromatids are separated Diploid cells (interphase  anaphase 1 of meiosis 1) 2n = 2 (each w/ 2 chromatids) Haploid cells telophase 1/cytokinesis through telophase 2/cytokinesis (at telophase 2 each chromosome has 1 chromatid now) 2n = 2 n = 1 I…PMAT…C, PMAT…C

End Result of Meiosis What is the result of meiosis in males? spermatogenesis (formation of sperm) all 4 daughter cells become sperm What is the result of meiosis in females? Oogenesis (formation of eggs) only 1 daughter cell becomes ovum (egg) other 3 daughter cells are small, nonfunctional polar bodies 1 egg cell & 3 smaller polar bodies are produced… polar body = A minute cell produced and ultimately discarded in the development of an oocyte, containing little or no cytoplasm but having one of the nuclei derived from the first or second meiotic division. 2n = 46 N = 23

spermatogenesis 4 sperm cells produced 2n = 4 N = 2

oogenesis 1 egg cell & 3 smaller polar bodies are produced… polar body = A minute cell produced and ultimately discarded in the development of an oocyte, containing little or no cytoplasm but having one of the nuclei derived from the first or second meiotic division. 2n = 4 N = 2

Fertilization What is fertilization? What is formed by fertilization? the fusion of sperm & egg What is formed by fertilization? a zygote (which will develop into a baby) What happens to the chromosome # after fertilization? diploid number restored (zygote has 2 of each chromosome) Through meiosis, the chromosome # is reduced to ½ the diploid (2n) #, resulting in the n or haploid # 2n = diploid n = haploid gametes only occurs in certain reproductive tissues…. results in 4 haploid cells that are genetically different from each other & the parent…. What if the # of chromosomes wasn’t reduced? Offspring would have 2x as many chromosomes…. So sperm must have ½ & egg must have ½ so that fertilization restores the diploid # in the newly formed zygote How is the reduction of chromosome # achieved??? Meiosis is a process of reduction division (First, homologous chromosomes are separated during meiosis I… the cell now has only one copy of each chromosome… but each chromosome is still double-stranded… the cell is now has the haploid # of chromosomes… Then, sister chromatids are separated during meiosis II… so each cell has one copy of each chromosome, which is now single-stranded….)

2n = 4 N = 2 (w/ 2 chromatids each)

N = 2 (1st w/ 2 chromatids, then as singles…)

2n = 4 N = 2

Review & Animations mitosis meiosis comparison mitosis & meiosis http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html http://www.johnkyrk.com/mitosis.html http://www.accessexcellence.org/RC/VL/GG/mitosis.php meiosis http://www.sumanasinc.com/webcontent/animations/content/meiosis.html http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html comparison mitosis & meiosis http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__comparison_of_meiosis_and_mitosis__quiz_1_.html http://www.pbs.org/wgbh/nova/miracle/divi_flash.html