lab 10 cell division/ mitosis & meiosis · 2020. 10. 29. · comparing mitosis and meiosis...

Cell Division/Mitosis & Meiosis

Lab 10

Objectives for this Week…By the end of today you should be able to…• Differentiate the different phases in the cell cycle• Compare and contrast the phases of mitosis in animal

and plant cells • Identify the different phases of mitosis.• Identify the different phases of meiosis in plant cells.

Part 1: Two Labster Simulations Linked through Canvas- complete by next Tuesday at 7pm

Part 2: Answer Review Questions- submit as a doc, docx, or pdf file by next Tuesday at 7pm

To Do:

Overview of Mitotic Cell Cycle

(duplication of cell contents)

(growth & increase in cytoplasm)(duplication of chromosomes)

(growth, preparation for

division)

Prophase

• In the cytoplasm:• Microtubules begin to emerge from

centrosomes, forming the spindle• Spindle fibers go to bind to the kinetochore

• In the nucleus:• Chromosomes coil and become compact• Nucleoli disappear• Nuclear envelope disappears

Early mitoticspindle

PROPHASECentrosome

Chromosome, consistingof two sister chromatids

Centromere

Metaphase

• Spindle is fully formed• Chromosomes align at the cell

equator• Kinetochores of sister chromatids are

facing the opposite poles of the spindleMetaphase

plate

METAPHASE

Spindle

Anaphase

• Sister chromatids separate at the centromeres

• Daughter chromosomes are moved to opposite poles of the cell

• Motor proteins move the chromosomes along the spindle microtubules

• Kinetochore microtubules shorten• The cell elongates due to

lengthening of kinetochore microtubules

ANAPHASE

Daughterchromosomes

Telophase• The cell continues to elongate• The nuclear envelope forms around

chromosomes at each pole, establishing daughter nuclei

• Chromatin uncoils • Nucleoli reappear• The spindle disappears• Often overlaps with cytokinesis

Nucleolusforming

TELOPHASE AND CYTOKINESIS

Cleavagefurrow

Nuclearenvelopeforming

• Cytoplasm is divided into separate cells

• Cleavage in animal cells • A cleavage furrow forms from a

contracting ring of microfilaments, interacting with myosin

• The cleavage furrow deepens to separate the contents into two cellsNucleolus

forming

TELOPHASE AND CYTOKINESIS

Cleavagefurrow

Nuclearenvelopeforming

Cytokinesis

Cytokinesis in Plants

1. Membrane-lined vesiclesaccumulate near themetaphase plate; thevesicles contain precursorsto the cell wall

2. Vesicles fuse togetherforming a cell plate thatgrows toward the parentcell wall

3. The newly formed plasmamembrane and cell wallfuse with the parent plasmamembrane and cell wall forming twodistinct daughter cells

cell wall

twodaughtercells

vesicles

plasmamembrane

Cell plate formation in plants

In Humans, Meiosis is Specific for GAMETES

• Gametes (sex cells)• Egg/sperm• Only half the number of chromosomes compared to other body cells

• Meiosis: process that produces 4 haploid daughter cells in diploid organisms

• Similar to mitosis EXCEPT• Two successive divisions (Meiosis I and Meiosis II)• Exchange of genetic material between homologous chromosomes

Multicellulardiploid adults(2n = 46)

MEIOSIS FERTILIZATION

MITOSIS

2n

and development Key

Sperm cell

n

n

Diploidzygote(2n = 46)

Diploid (2n)Haploid (n)

Egg cellHaploid gametes (n = 23)

MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE

Sister chromatidsremain attached

Pair ofhomologouschromosomes

INTERPHASE

Sisterchromatids

Homologouschromosomespair up andexchangesegments.

Chromosomesduplicate.

Pairs of homologouschromosomesline up.

Pairs of homologouschromosomessplit up.

Nuclearenvelope

Chromatin

Centromere

Microtubulesattachedto chromosome

Sites of crossing over

Spindle

Centrosomes (with centriolepairs)

PROPHASE I METAPHASE I ANAPHASE I

Figure 8.14a

INTERPHASE

Nuclear envelope Chromatin

Centrosomes (with centriolepairs)

Figure 8.14aa

• Like mitosis, meiosis is preceded by an interphase during which chromosomes duplicate.

• Each chromosome then consists of two identical chromatids.


Sisterchromatids Centromere

Microtubules attachedto chromosome


Spindle

PROPHASE I METAPHASE I

Figure 8.14ac

• As the chromosomes coil up, specialproteins cause the homologouschromosomes to stick together in pairs.The resulting structure has four chromatids. Within each set, chromatidsof the homologous chromosomesexchange corresponding segments(“crossover”).

• As prophase I continues, the chromosomes coil up further, a spindle forms, and the homologous pairs are moved toward the center of the cellCell analysis:

2n = 44 Chromosomes8 Chromatids8 DNA molecules


Sisterchromatids Centromere

Microtubules attachedto chromosome


Spindle

PROPHASE I METAPHASE I

Figure 8.14ac

•Homologous pairs are aligned in the middle of the cell.

•Sister chromatids of each chromosome are still attached at their centromeres, where they are anchored to spindle microtubules.

• Notice that for each chromosome pair, the spindle microtubules attached to one homologous chromosome come from one pole of the cell, and the microtubules attached to the other chromosome come from the opposite pole. With this arrangement, the homologous chromosomes are poised to move toward opposite poles of the cell.

Cell analysis:2n = 44 Chromosomes8 Chromatids8 DNA molecules

independent/random assortment

TELOPHASE I AND CYTOKINESISSister chromatidsremain attached

ANAPHASE I

Cleavagefurrow

TELOPHASE I AND CYTOKINESIS

Figure 8.14ad

• The attachment between the homologous chromosomes of each pair breaks, and the chromosomes now migrate toward the poles of the cell.

•In contrast to mitosis, the sister chromatids migrate as a pair instead of splitting up. They are separated not from each other, but from their homologous partners.

Cell analysis:2n = 44 Chromosomes8 Chromatids8 DNA molecules

TELOPHASE I AND CYTOKINESISSister chromatidsremain attached

ANAPHASE I

Cleavagefurrow

TELOPHASE I AND CYTOKINESIS

Figure 8.14ad

• In telophase I, the chromosomes arrive at the poles of the cell. When they finish their journey, each pole has a haploid chromosome set, although each chromosome is still in duplicate form. Usually, cytokinesis occurs along with telophase I, and two haploid daughter cells are formed.

Cell analysis:n = 22 Chromosomes4 Chromatids4 DNA molecules


After Meiosis I: two haploiddaughter cells

TELOPHASE II AND

CYTOKINESIS

Sister chromatidsseparate

ANAPHASE II

Cleavagefurrow

TELOPHASE I AND

CYTOKINESIS

Two haploidcells form;chromosomesare stilldoubled.

MEIOSIS II: SISTER CHROMATIDS SEPARATEPROPHASE II METAPHASE II

During another round of cell division, the sisterchromatids finally separate; four haploiddaughter cells result, containing single

chromosomes.

Haploid daughtercells forming

Figure 8.14b

PROPHASE II METAPHASE II

Figure 8.14bb

• Meiosis II is essentially the same as mitosis. The important difference is that meiosis II starts with a haploid cell that has NOT undergone a chromosome duplication during the preceding interphase.

•During prophase II, a spindle forms and moves the chromosomes toward the middle of the cell.



PROPHASE II METAPHASE II

Figure 8.14bb

• During metaphase II, the chromosomes are aligned as they are in mitosis, with the microtubules attached to the sister chromatids of each chromosome coming from opposite poles.



Chromosomes align at the metaphase plate

TELOPHASE II AND CYTOKINESIS


ANAPHASE II

Haploid daughter cells forming

Figure 8.14bd

• In anaphase II, the centromeres of sister chromatids separate, and the sister chromatids of each pair move toward opposite poles of the cell.



“Sister” chromatids separate (may no longer be identical due to crossing over that occurred during Prophase I)

TELOPHASE II AND CYTOKINESIS


ANAPHASE II

Haploid daughter cells forming

Figure 8.14bd

• In telophase II, nuclei form at the cell poles, and cytokinesis occurs at the same time. There are now 4 daughter cells, each with the haploid number of single chromosomes.





Final result of Meiosis: 4 non-identical haploid daughter cells

• crossing-over: the exchange of genetic material between homologous chromosomes

• random assortment: the pairs of homologous chromosome are divided in half to form haploid cells, and this separation (assortment) of homologous chromosomes is random. crossing-over

Mechanisms of Genetic Diversity:

Crossing Over & Random Assortment

Mechanisms of Genetic Diversity:

Crossing Over & Random Assortment

Comparing Mitosis and Meiosis• Similarities:

• Chromosomes duplicate during S phase in interphase of the cell cycle

• Mitosis and Meiosis II are similar because during anaphase sister chromatids separate

• Differences:• Mitosis uses 1 cell division, meiosis uses 2• Mitosis produces 2 diploid daughter

cells, meiosis produces 4 haploid daughter cells

• During meiosis homologous chromosomes pair

• Meiosis has crossing over during Prophase I

Part 1Two Labster Exercises:

Mitosis & Meiosis

Linked through Canvas Due next Tuesday by 7pm. 26

Part 2

Answer Review Questions

27Submit through Canvas (doc, docx, or pdf files only).

Due next Tuesday by 7pm.

What Is a Venn Diagram? (Q6)• A Venn diagram is an illustration that uses circles to show

the relationships among things or finite groups of things. • circles that overlap share those traits• circles that do not overlap do not share those traits

• Venn diagrams help to visually represent the similarities and differences between two or more concepts, examples:

Adifferent

Bdifferent

Cdifferent

Ddifferent

Edifferent

Fdifferent

Gdifferent

similarbtw A&B

similarbtw CDE

similarbtw DE

similarbtw CE

similarbtw CD

no similarities

Other Venn Diagram Examples

Design a Venn Diagram in PPT

Venn Diagram Resources If Needed:• Getting Started with Venn Diagrams in Under 5 Minutes:

• https://smartdraw.atlassian.net/wiki/spaces/HELP/pages/398459068/Venn+Diagram

• Venn Diagram:• https://www.smartdraw.com/venn-diagram/

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lab 10 cell division/ mitosis & meiosis · 2020. 10. 29. · comparing mitosis and meiosis...

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