GENETICS - CLUTCH CH.9 MITOSIS AND MEIOSIS.

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CONCEPT: MITOSIS Mitosis is a type of cell division that produces daughter cells Interphase is the initial stage of the cell cycle, and is the period between divisions - G1, which is a growth

two copies of the same chromosome - G2, which is a growth phase after DNA replication Prophase is the first stage of cell division - Centrioles move to opposite ends of the cells - Spindle

2 CONCEPT: MITOSIS Mitosis is a type of cell division that produces daughter cells Interphase is the initial stage of the cell cycle, and is the period between divisions - G1, which is a growth phase before DNA replication - G0 is a non-proliferative phase that the cell enters if it s not ready to replicate the DNA - S, is the phase with DNA replication - Sister chromatids are the two copies of the same chromosome - G2, which is a growth phase after DNA replication Prophase is the first stage of cell division - Centrioles move to opposite ends of the cells - Spindle fibers are microtubules that extend out from the centrioles - Nuclear envelop breaks down - Chromatin (DNA + pt) begins to condense - Cohesion is a protein that holds two sister chromatids Page 2

3 Prometaphase is the period of chromosome movement to the middle of the cell Metaphase is when the chromosomes are lined up in the middle of the cell - Metaphase plate is the midline region of the cell - Kinetochore is a protein complex that attaches to the chromosome centromere - The kinetochore attaches the chromosome to the spindle fibers - Cohesion is beginning to be degraded Page 3

4 Anaphase is when the chromosomes begin to segregate into daughter cells - Cohesion is completely degraded - Disjuction is the process of separating homologous chromosomes Telophase is the final stage of mitosis - A complete set of chromosomes are present at each cell pole Cytokinesis is the process of dividing the cytoplasm into two cells - Cell plate is formed by plant cells, which helps form the plant cell wall - Cleavage furrow is the invagination of the cell membrane, which forms two cells Page 4

5 Cell-Cycle Regulation The cell cycle must be intricately Checkpoints have been set up by the cell to ensure the cell is replicating and dividing properly - G1/S Checkpoint ensures the cell size is appropriate for division - G2/M Checkpoint ensures that DNA has been replicated correctly - M Checkpoint ensures the spindle fibers have formed correctly Certain proteins are responsible for these checkpoints - Cyclin dependent kinases are enzymes that add phosphates to molecules - Phosphates can activate or deactivate cell cycle proteins - Cyclins are master control proteins that ensure proper regulation Page 5

6 PRACTICE: 1. Which of the following is the correct order of mitosis steps? a. Interphase - metaphase - prophase - anaphase - telophase cytokinesis b. Interphase prophase metaphase anaphase telophase cytokinesis c. Interphase prophase metaphase telophase anaphase cytokinesis d. Cytokinesis prophase metaphase anaphase telophase interphase 2. In which step do the chromosomes begin to separate into daughter cells? a. Interphase b. Prophase c. Prometaphase d. Metaphase e. Anaphase f. Telophase g. Cytokinesis Page 6

7 3. In which step does the cleavage furrow form a. Interphase b. Prophase c. Prometaphase d. Metaphase e. Anaphase f. Telophase g. Cytokinesis 4. In which step is the DNA replicated? a. Interphase b. Prophase c. Prometaphase d. Metaphase e. Anaphase f. Telophase g. Cytokinesis Page 7

8 5. In which step does the chromatin begin to condense a. Interphase b. Prophase c. Prometaphase d. Metaphase e. Anaphase f. Telophase g. Cytokinesis 6. Which checkpoint is responsible for ensuring the DNA was replicated properly? a. G1/S b. G2/M c. M d. C Page 8

9 7. Cohesion is a protein responsible for what? a. Forming the spindle fibers b. Holding non-sister chromatids together c. Connecting the spindle fibers to the centromere d. Holding sister chromatids together Page 9

CONCEPT: MEIOSIS Overview of Meiosis Meiosis is the process of cell division which creates daughter cells with the genetic material There are two divisions - Reductional division is the first

10 CONCEPT: MEIOSIS Overview of Meiosis Meiosis is the process of cell division which creates daughter cells with the genetic material There are two divisions - Reductional division is the first division, and the chromosomes are reduced by ½ - But at this point there are two copies of each chromosome - Equational division is the second division, and the sister chromatids are divided into daughter cells There are many chromosomal during meiosis - At the beginning of meiosis you start of with homologous chromosomes - After the DNA is replicated, there are two sister chromatids for each chromosome - A bivalent is the pair of two homologous chromosomes - A tetrad refers to the four chromatids that form after replication - A dyad refers to two sister chromatids Page 10

Meiosis Steps Meiosis is completed in two parts meiosis I and meiosis II Prophase I involves 5 steps - Leptonema: Chromatin begins condending into chromosomes - Zygonema: Chromosomes align, and a

11 Meiosis Steps Meiosis is completed in two parts meiosis I and meiosis II Prophase I involves 5 steps - Leptonema: Chromatin begins condending into chromosomes - Zygonema: Chromosomes align, and a synaptonemal complex forms between the homologs - Pachynema: Crossing over occurs, can see chiasmata which forms between crossing over homologs - Diplonema: Chromosomes remain as tetrads - Diakinesis:: Chromosomes begin to pull apart, but the chiasmata keep them together Metaphase I: The tetrads line up in the metaphase plate - The homologous chromosomes lie on either side of the metaphase plate Page 11

doesn t occur properly Telophase I: The nuclear membrane begins to reform around dyads Cytokinesis: The cells

12 - Two sister chromatids lie on either side of the metaphase plate Anaphase I: Each dyad separates to one cell pole - Disjuction is when the homologous chromosomes separate properly - Nondisjunction is when the separation doesn t occur properly Telophase I: The nuclear membrane begins to reform around dyads Cytokinesis: The cells form two haploid cells Prophase II: Is a short phase where two cells have one pair of sister chromatids Page 12

13 Metaphase II: Is when the sister chromatids line up on either side of the metaphase plate separated Anaphase II: The sister chromatids are Telophase II: One chromosome is present at each pole Cytokinesis: Cytoplasmic division create four haploid cells Page 13

14 PRACTICE 2. In which step of prophase I does crossing-over occur? a. Leptonema b. Zygonema c. Pachynema d. Diplonema e. Diakinesis 3. Are the two daughter cells produced from meiosis I diploid or haploid? a. Diploid b. Haploid Page 14

15 4. Are the four daughter cells produced from meiosis II diploid or haploid? a. Diploid b. Haploid 5. Which of the following are sources of genetic variation during meiosis? a. Crossing over, independent assortment b. Crossing over, DNA replication c. DNA replication, independent assortment d. Disjunction, crossing over Page 15

16 6. During which stage of meiosis do sister chromatids separate? a. Prophase I b. Anaphase I c. Prophase II d. Anaphase II Page 16

17 CONCEPT: DEVELOPMENT OF ANIMAL GAMETES In animals, there are development systems that the sperm and the egg Spermatogenesis is the process that creates the gametes in the male animal - Diploid primordial germ cells are the cells that use meiosis to create male gametes 1. Spermatogonia are formed via mitotic division of the primordial germ cells 2. The primary spermatocyte enters into meiosis (diploid) 3. The secondary spermatocyte are two haploid cells formed via meiosis I 4. The spermatids are formed via meiosis II (haploid) Spermatogonium Spermacyte I Spermacyte II Spermatoid Page 17

Oogenesis is the process that creates the female gametes - Diploid primordial germ cells also exist in females 1. Oogonia are formed via mitotic division of the primordial germ cells 2.

18 Oogenesis is the process that creates the female gametes - Diploid primordial germ cells also exist in females 1. Oogonia are formed via mitotic division of the primordial germ cells 2. The primary oocytes enter into prophase I (diploid) 3. Meiosis I occurs, but the cytoplasm is divided unequally - The secondary oocyte is the larger cell formed during meiosis I - The first polar body is the smaller cell formed during meiosis I 4. Meiosis II occurs on the secondary oocyte, and again there is an unequal division of cytoplasm - The ovum is the mature female gamete (haploid) - The secondary polar body is the smaller cell formed during meiosis II Page 18

19 PRACTICE: 1. Horse diploid cells contain 64 chromosomes (2n=64). How many chromosomes will be present in spermatogonium cells? a. 32 b. 64 c. 128 d Horse diploid cells contain 64 chromosomes (2n=64). How many chromosomes will be present in primary oocyte cells? a. 32 b. 64 c. 128 d. 40 Page 19

20 3. Horse diploid cells contain 64 chromosomes (2n=64). How many chromosomes will be present in spermatids cells? a. 32 b. 64 c. 128 d What is the correct term for the mature female gamete? a. Ovum b. Secondary polar body c. Secondary oocyte d. Oogonia Page 20

CONCEPT: DEVELOPMENT OF PLANT GAMETES When it comes to plants, there is a lot of different Unisexual or dioecious or gonochoric means that the organisms contains male OR female organs Bisexual or

21 CONCEPT: DEVELOPMENT OF PLANT GAMETES When it comes to plants, there is a lot of different Unisexual or dioecious or gonochoric means that the organisms contains male OR female organs Bisexual or monoecious or hermaphroditic means that the organism contains male AND female organs Intersex refers to organisms with an intermediate sexual condition. These organisms are usually sterile There are two types of sexual differentiation - Primary sexual differentiation refers to the types of gametes produced in the sexual organs - Secondary sexual differentiation refers to the overall sexual appearance of the organism Formation of Plant Gametes Plants, like animals have two life stages: the haploid (gametophyte) and diploid (sporophyte) stages Both the gametophyte and the sporophyte are used to create - Haploid spores are created via meiosis of the sporophyte - The spores undergo mitosis to create gametes The structures of the sporophyte and gametophyte a different - The flower is the sporophyte, and the gametophyte is only a few haploid cells within the flower Page 21

22 The plant can contain both male and female - The male stamen contains microsporocytes (diploid) undergo meiosis to form haploid microspores - Microspores undergo mitosis to produce haploid pollen (gametophyte), with 2 nuclei - The female stigma contains megasporocytes (diploid) undergo meiosis to form haploid megaspores - Only one survives it divides via mitosis to create eight haploid nuclei (gametophyte) Meiosis Mitosis Microsporocytes Diploid Microspores Haploid Gametophyte Haploid Fertilization occurs when the pollen lands on the stigma - Fertilization between the pollen and female gametophyte (embryo sac) creates a diploid zygote Chlamydomonas Reproduction Chlamydomonas is an algae that has an interesting life cycle For most of its life, it is a haploid organism which reproduces via mitosis Certain conditions result in fusion of two haploid organisms creating a diploid organism - Meiosis occurs when the condition is removed producing zoospores, which are haploid daughter cells Not all chlamydomonas organisms are able to - There are two mating types: mt + and mt - - Mt + mates only with mt - cells - The two types are isogametes, meaning that they are morphologically indistinguishable Page 22

23 PRACTICE: 1. Which of the following terms can be used to describe an organism that contained either male or female sex organs, but not both. a. Bisexual b. UnIsexual c. Intersex d. Sexually differentiated Page 23

24 2. Which of the following is the diploid life cycle stage in plants? a. Gametophyte b. Spores c. Sporophyte d. Gametes 3. In the alternations of generations life cycle, which cellular division process is used to create gametes? a. Meiosis b. Mitosis Page 24

25 4. Microsporocytes undergo which cellular process to form microspores? a. Meiosis b. Mitosis 5. True or False: Megaspores are created in the male stamen. a. True b. False Page 25

STUDY UNIT 1 MITOSIS AND MEIOSIS. Klug, Cummings & Spencer Chapter 2. Morphology of eukaryotic metaphase chromosomes. Chromatids

STUDY UNIT 1 MITOSIS AND MEIOSIS Klug, Cummings & Spencer Chapter 2 Life depends on cell division and reproduction of organisms. Process involves transfer of genetic material. New somatic (body) cells