Biology Chapter on Cell Division and Cancer

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Questions and Answers

Which cell type is known for dividing frequently?

  • Bone cells
  • Intestinal cells (correct)
  • Blood cells
  • Neuronal cells

Cancerous cells have fully functional cell cycle checkpoints.

False (B)

What do cells enter when they do not receive the go-ahead signal?

G0 phase

The cell cycle is driven by specific chemical signals present in the ______.

<p>cytoplasm</p> Signup and view all the answers

Match the checkpoints to their corresponding phases in the cell cycle:

<p>G1 checkpoint = Checks for cell size and DNA integrity G2 checkpoint = Checks for DNA replication completeness M checkpoint = Checks for chromosome alignment</p> Signup and view all the answers

What is one consequence of cancer cells losing their checkpoints?

<p>They become immortal. (C)</p> Signup and view all the answers

Molecular clocks are not involved in regulating the cell cycle.

<p>False (B)</p> Signup and view all the answers

Who were HeLa cells named after?

<p>Henrietta Lacks</p> Signup and view all the answers

What type of cell division produces sperm and egg cells?

<p>Meiosis (D)</p> Signup and view all the answers

Most DNA is packaged into ribosomes.

<p>False (B)</p> Signup and view all the answers

What are the units of heredity made up of segments of DNA?

<p>genes</p> Signup and view all the answers

Humans have _____ pairs of chromosomes in somatic cells.

<p>23</p> Signup and view all the answers

What is the primary function of cellular division in multicellular eukaryotes?

<p>Development from a fertilized egg (B)</p> Signup and view all the answers

Meiosis results in identical daughter cells.

<p>False (B)</p> Signup and view all the answers

What is a karyotype?

<p>An ordered display of chromosome pairs (B)</p> Signup and view all the answers

What is chromatin?

<p>A complex of DNA and protein that condenses during cell division.</p> Signup and view all the answers

Match the terms with their correct descriptions:

<p>Gene = Unit of heredity Gamete = Reproductive cell Locus = Specific position of a gene on a chromosome Heredity = Transmission of traits from one generation to another</p> Signup and view all the answers

In humans, haploid cells contain _____ chromosomes.

<p>23</p> Signup and view all the answers

Offspring can exhibit variation in appearance due to genetic differences.

<p>True (A)</p> Signup and view all the answers

Match the following phases with their major functions during the cell cycle:

<p>Mitosis = Division of the nucleus Cytokinesis = Division of the cytoplasm Interphase = Preparation for cell division Meiosis = Production of gametes</p> Signup and view all the answers

What is the scientific study of heredity and variation called?

<p>genetics</p> Signup and view all the answers

What happens when cellular checkpoints malfunction?

<p>It can lead to uncontrolled cell growth. (D)</p> Signup and view all the answers

Plant cells undergo exactly the same process of cytokinesis as animal cells.

<p>False (B)</p> Signup and view all the answers

What is the life cycle of a cell referred to as?

<p>Cell cycle</p> Signup and view all the answers

Eukaryotic cells typically have a characteristic number of _____ in each cell nucleus.

<p>chromosomes</p> Signup and view all the answers

What type of division does meiosis represent?

<p>A special type of division producing gametes (D)</p> Signup and view all the answers

What are the joined copies of the original chromosome called?

<p>Sister chromatids (B)</p> Signup and view all the answers

During anaphase, sister chromatids are still attached to each other.

<p>False (B)</p> Signup and view all the answers

Name the phase of the cell cycle where DNA replication occurs.

<p>S phase</p> Signup and view all the answers

The __________ is the narrow 'waist' of a duplicated chromosome.

<p>centromere</p> Signup and view all the answers

Match the following stages of mitosis with their descriptions:

<p>Prophase = Chromosomes become visible and mitotic spindle forms Metaphase = Chromosomes align at the metaphase plate Anaphase = Sister chromatids separate toward opposite poles Telophase = Nuclear envelope reappears and chromosomes decondense</p> Signup and view all the answers

What structure controls chromosome movement during mitosis?

<p>Mitotic spindle (D)</p> Signup and view all the answers

Cytokinesis occurs after the completion of mitosis.

<p>True (A)</p> Signup and view all the answers

What is the role of kinetochore microtubules during mitosis?

<p>They attach to the kinetochores of chromosomes to facilitate their movement.</p> Signup and view all the answers

During __________, the nuclear envelope fragments and chromosomes become more condensed.

<p>prometaphase</p> Signup and view all the answers

What phase of interphase involves cell growth and preparation for DNA synthesis?

<p>G1 phase (A)</p> Signup and view all the answers

In plant cells, cytokinesis occurs through the formation of a cleavage furrow.

<p>False (B)</p> Signup and view all the answers

Describe what happens to chromosomes at the metaphase plate.

<p>Chromosomes align along the metaphase plate with their centromeres lying at this imaginary plane.</p> Signup and view all the answers

Cytokinesis in animal cells involves the formation of a __________.

<p>cleavage furrow</p> Signup and view all the answers

Which protein complex attaches sister chromatids?

<p>Cohesins (B)</p> Signup and view all the answers

What is the primary difference between asexual and sexual reproduction?

<p>Asexual reproduction produces genetically identical offspring while sexual reproduction results in unique combinations of genes. (B)</p> Signup and view all the answers

Human females have a homologous pair of X chromosomes.

<p>True (A)</p> Signup and view all the answers

What are the two types of cells produced by meiosis?

<p>Gametes</p> Signup and view all the answers

The fertilized egg is called a __________.

<p>zygote</p> Signup and view all the answers

What process is primarily involved in the production of gametes?

<p>Meiosis (C)</p> Signup and view all the answers

Mitosis results in four daughter cells.

<p>False (B)</p> Signup and view all the answers

How many pairs of chromosomes do human somatic cells typically have?

<p>23</p> Signup and view all the answers

A diploid cell is represented as __________.

<p>2n</p> Signup and view all the answers

Which type of chromosomes does a human sperm cell carry?

<p>Either X or Y chromosomes (B)</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Somatic Cells = Non-reproductive cells with two sets of chromosomes Gametes = Reproductive cells that are haploid Diploid = Cells containing two sets of chromosomes Haploid = Cells containing one set of chromosomes</p> Signup and view all the answers

Aneuploidy refers to the normal number of chromosomes in a cell.

<p>False (B)</p> Signup and view all the answers

What is the primary purpose of crossing over during meiosis?

<p>Genetic variation</p> Signup and view all the answers

The union of gametes is called __________.

<p>fertilization</p> Signup and view all the answers

How many daughter cells are produced in meiosis?

<p>Four (B)</p> Signup and view all the answers

What is the role of mitosis in the life cycle of an organism?

<p>Growth and tissue repair</p> Signup and view all the answers

Flashcards

Cellular Division

The ability of organisms to produce more of their own kind.

Cell Cycle

The life of a cell from formation to its own division.

Mitosis

The process where a cell divides into two nearly identical daughter cells.

Meiosis

The process of cell division that produces non-identical daughter cells, resulting in gametes (sperm and egg cells).

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Genome

All the DNA in a cell, regardless of the number of DNA molecules it contains.

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Chromosomes

Packages of DNA in a cell, visible during cell division.

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Chromatin

A complex of DNA and protein (histones) that condenses during cell division, forming chromosomes.

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Meiosis

A special type of cell division that produces gametes (sperm and egg cells)

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Mitosis

The process of cell division that produces two nearly identical daughter cells.

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Genome

The complete set of instructions for life, encoded in DNA.

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Frequently Dividing Cells

Cells whose job it is to rapidly divide and replace old or damaged cells. For example, intestinal cells.

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Rarely Dividing Cells

Cells that rarely divide once they have differentiated and matured. For example, nerve cells.

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Cancerous Cells

Cells that have lost their normal cell cycle controls and divide uncontrollably, leading to tumor formation.

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Molecular Clocks

The internal chemical signals that regulate the progression of the cell cycle.

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Checkpoints

Specific points in the cell cycle where the cell pauses to ensure that all necessary conditions are met before proceeding to the next stage.

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G0 Phase

A non-dividing state that some cells enter when they don't receive the go-ahead signal to proceed through the cell cycle.

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HeLa Cells

Immortal cells that are derived from a human cervical cancer cell line and have continuously divided in culture since 1951. They have lost their cell cycle checkpoints and can divide indefinitely in the presence of nutrients.

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Centromere

The narrow region where two sister chromatids are most closely attached.

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Cohesins

Protein complexes that hold sister chromatids together.

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Sister Chromatids

Joined copies of the original chromosome, attached along their lengths by cohesins.

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Cytokinesis

The division of the cytoplasm.

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Prometaphase

Phase where the nuclear envelope fragments and microtubules invade the nuclear area.

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Metaphase

Phase where the chromosomes align at the middle of the cell.

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Telophase

Phase where two daughter nuclei form and chromosomes decondense.

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Mitotic Spindle

A structure made of microtubules that controls chromosome movement during mitosis.

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Kinetochore

A protein complex associated with centromeres, where microtubules attach.

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What is meiosis?

Specialized cell division that produces gametes (sperm and egg cells), resulting in non-identical daughter cells.

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Define heredity.

The transmission of traits from parents to offspring.

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What is variation?

Differences in appearance observed among offspring from parents and siblings.

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What does genetics explore?

The scientific study of heredity and variation.

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What are genes?

Units of heredity made up of segments of DNA.

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What is a locus?

A gene's specific location on a chromosome.

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What are gametes?

Reproductive cells (sperm and egg) that carry genes to the next generation.

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What is a karyotype?

An organized display of chromosome pairs from a cell.

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Asexual Reproduction

A type of reproduction where offspring inherit genetic material from a single parent, resulting in clones with identical genetic makeup.

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Clone

Offspring that are genetically identical to their single parent.

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Sexual Reproduction

Two parents contribute genetic material to offspring, resulting in unique combinations of genes.

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Somatic Cells

Cells that are not involved in reproduction. Diploid cells have two sets of chromosomes.

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Gametes

Reproductive cells, such as sperm and egg cells. Haploid cells have one set of chromosomes.

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Diploid

The number of chromosomes in a cell, where each chromosome has a homologous pair.

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Haploid

The number of chromosomes in a cell, where each chromosome is unique.

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Homologous Chromosomes

The two chromosomes in a pair that have the same length, shape, and genes.

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Crossing Over

The process by which homologous chromosomes exchange genetic information during meiosis I.

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Aneuploidy

A condition where a cell has an abnormal number of chromosomes.

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Fertilization

The union of a sperm and egg cell, resulting in a zygote.

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Zygote

A fertilized egg cell.

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Life Cycle

The life cycle of an organism, including all stages of reproduction.

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Study Notes

Learning Objectives

  • Understand the functions of cellular division and the organization of genetic material in chromatin/chromosomes.
  • Define key chromosomal/genetic material terminology.
  • Understand the major phases and processes occurring in the cell cycle during mitosis.
  • Explain how the mitotic spindle contributes to chromosomal movement in all phases of mitosis.
  • Understand the difference between animal and plant cell cytokinesis.
  • Understand why cellular checkpoints are important and what happens when they malfunction.
  • Explain how genetic material is passed through generations.
  • Understand chromosomal numbers in humans, haploid vs diploid cells (and examples in the body), human life cycle.
  • Describe the differences between asexual and sexual reproduction.
  • Explain the major outcomes of meiosis, major phases of meiosis I and meiosis II, how genetic diversity occurs.
  • Compare and contrast mitosis and meiosis.
  • Cellular division is crucial for organism growth and survival
  • The continuity of life is based on cell division.

Cellular Division

  • The ability of organisms to produce more of their own kind.
  • Mitosis and meiosis are types of cell division.
  • Mitosis results in two identical daughter cells.
  • Meiosis results in four non-identical daughter cells.

Functions of Cellular Division

  • In unicellular organisms: Division of one cell reproduces the entire organism.
  • In multicellular eukaryotes: Dependent on cell division for development from a fertilized egg, growth, and repair.

Introducing the Cell Cycle

  • Cell division is an integral part of the cell cycle.
  • Cell cycle: The life of a cell from formation to its own division.
  • Most cell division results in two daughter cells with identical genetic information.
  • The exception is meiosis -- a special type of division that can produce sperm and egg cells (gametes).
  • Meiosis produces non-identical daughter cells.

Cellular Organization of the Genetic Material

  • Genome: All the DNA in a cell
  • A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells).
  • DNA molecules in a cell are packaged into chromosomes.
  • Eukaryotic chromosomes consist of chromatin.
  • Chromatin: A complex of DNA and protein (histones) that condenses during cell division.
  • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.

Distribution of Chromosomes During Eukaryotic Cell Division

  • In preparation for cell division, DNA is replicated, and the chromosomes condense.
  • Each duplicated chromosome has two sister chromatids.
  • Sister chromatids: Joined copies of the original chromosome, attached along their lengths by cohesins.
  • Cohesins: Protein complexes that attach sister chromatids.
  • The centromere: the narrow waist of a duplicated chromosome, where two chromatids are most closely attached.

The Two Major Phases of the Cell Cycle

  • Interphase (G1, S, and G2): Cell growth and copying of chromosomes in preparation for cell division (about 90% of the cell cycle).
  • G1 phase (First gap): Cell growth, increases in size, gets ready for S phase.
  • S phase (Synthesis): DNA replication occurs.
  • G2 phase (Second gap): Cell continues to grow, gets ready for mitosis.
  • Mitotic phase (Mitosis and Cytokinesis): Mitosis: the division of the genetic material in the nucleus, and Cytokinesis: the division of the cytoplasm.

Mitosis Consists of 5 Stages

  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase and Cytokinesis

G2 of Interphase

  • A nuclear envelope encloses the nucleus.
  • Two centrosomes have formed, regions that organize microtubules.
  • Chromosomes duplicated in S phase cannot be seen.

Prophase

  • Chromatin fibers tightly coil into discrete chromosomes, becoming visible.
  • Duplicated chromosomes appear as two sister chromatids joined at centromeres.
  • Mitotic spindle begins to form.
  • Centrosomes and the microtubules extending from centrosomes.
  • Centrioles move away from each other

Prometaphase

  • Nuclear envelope fragments, chromosomes are even more condensed.
  • Microtubules from each centrosome invade nuclear area.
  • Kinetochore: protein structure at the centromere on each sister chromatid.
  • Some microtubules become kinetochore microtubules, jerking chromosomes back and forth.
  • Any non kinetochore microtubules elongate the cell

Metaphase

  • Centrosomes now at opposite poles of the cell.
  • Chromosomes have arrived at the metaphase plate, an imaginary plane at the middle of the cell.
  • Centromeres lie at metaphase plate.
  • Kinetochore of each sister chromatid attach to kinetochore microtubules.

Anaphase

  • Shortest phase of mitosis.
  • Cohesins between chromatids are cleaved, allowing each pair to separate (becoming an independent chromosome).
  • Two new daughter chromosomes moving towards opposite poles.
  • Centromeres lead, because microtubules attached to kinetochore (at centromere).

Telophase and Cytokinesis

  • Two daughter nuclei form.
  • Nuclear envelope reappears.
  • Chromosomes start to decondense.
  • Mitosis is now complete, creating two genetically identical nuclei.
  • Cytokinesis: Division of the cytoplasm.
  • Involves formation of a cleavage furrow, pinching cell in two (animal cells).
  • Cell plate forms during cytokinesis in plant cells.

Animal Cell Mitosis (time-lapse) and Plant Cell Cytokinesis (in onion root cells)

  • Both animal and plant cells undergo mitosis and cytokinesis, but the mechanisms for cytokinesis differ.

BioFlix Animation: Mitosis

  • Digital animation.
  • Demonstrates stages of mitosis

The Mitotic Spindle

  • A structure made of microtubules that controls chromosome movement during mitosis.
  • In animal cells, assembly of spindle microtubules begins the centrosome (Microtubule-organizing center [MTOC])
  • The centrosome replicates during interphase and two centrosomes migrate to opposite ends of the cell during prophase and prometaphase
  • During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes, and begin to move the chromosomes.
  • Kinetochores are protein complexes associated with centromeres
  • At metaphase, the chromosomes are all lined up at the metaphase plate.
  • In anaphase, cohesins are cleaved by the enzyme separase.
  • Sister chromatids separate and move along the kinetochore microtubules toward opposite sides of the cell.
  • The microtubules shorten by depolymerizing at their kinetochore ends.
  • Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cell.
  • Cytokinesis begins during anaphase or telophase, and the spindle eventually disassembles

Comparing cytokinesis in animal and plant cells

  • In animal cells, cytokinesis involves a cleavage furrow.
  • A contractile ring of microfilaments forms during cytokinesis in animal cells.
  • In plant cells, a cell plate forms during cytokinesis.
  • Vesicles contain cell wall material derived from the Golgi apparatus.

How do cells know when to divide?

  • Cell Cycle is tightly regulated.
  • Some cells divide frequently (intestinal cells) and others rarely divide (neuronal cells).
  • Cancerous cells escape the usual controls and proliferate.

Molecular Clocks

  • The cell cycle is driven by specific chemical signals present in the cytoplasm.
  • The cell cycle is directed by a distinct cell cycle control system, which is similar to a clock.
  • The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received.

Cellular Checkpoints

  • Changes in regulatory protein concentrations drive the cell cycle.
  • Three important checkpoints are in the G1, G2, and M phases
  • If the cell doesn’t receive the go-ahead signal, it will exit the cycle and switch to a non-dividing state (G0 phase).

Cancer Cells

  • Lose their cell cycle checkpoints due to internal and/or external factors.
  • Become immortal and continuously divide provided they have enough nutrients
  • HeLa cells: Harvested from a woman named Henrietta Lacks (1951)

Chapter 13: Meiosis

  • A special type of cell division that can produce sperm and egg cells (gametes).
  • Produces non-identical daughter cells.
  • Heredity is the transmission of traits from one generation to the next.
  • Variation is demonstrated by the differences in appearance that offspring show from parents and siblings.
  • Genetics is the scientific study of heredity and variation.

Inheritance of Genetic Material

  • Offspring inherit genetic material from parents.
  • Genes are the units of heredity and are made of segments of DNA.
  • Locus (plural, loci): A gene's specific position along a chromosome.
  • Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs).
  • Offspring acquire genes from parents by inheriting chromosome
  • Most DNA packaged into chromosomes.
  • Human somatic cells have 23 pairs of chromosomes (total of 46).
  • Karyotype: An ordered display of the pairs of chromosomes from a cell.

Comparison of Asexual and Sexual Reproduction

  • In asexual reproduction, a single individual passes all of its genes to its offspring.
  • A clone is a group of genetically identical individuals from the same parent.
  • In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents.

Cellular Organization of the Genetic Material

  • Somatic cells: Non-reproductive cells, with two sets of chromosomes (diploid).
  • Gametes: Reproductive cells (sperm and eggs), with half as many chromosomes as somatic cells (haploid). In an unfertilized egg, the sex chromosome is X, in a sperm either X or Y.

Sets of Chromosomes in Human Cell

  • Human somatic cells have 23 pairs of chromosomes.
  • The sex chromosomes are called X and Y.
  • Human females have a homologous pair of X chromosomes (XX).
  • Human males have one X and one Y chromosome.
  • The remaining 22 pairs of chromosomes are called autosomes.
  • Aneuploidy: Abnormal number of chromosomes.

Sets of Chromosomes in a Cell

  • The homologous chromosomes, or homologs, are the two chromosomes in each pair.
  • Chromosomes in a homologous pair are the same length and shape, and carry similar genes.
  • Each pair of homologous chromosomes includes one chromosome from each parent.
  • Nonsister chromatids are chromatids in a homologous pair, one from each parent.

Behavior of Chromosome Sets in the Human Life Cycle

  • A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism.
  • Fertilization: The union of gametes.
  • The fertilized egg is called a zygote, which has one set of chromosomes from each parent.
  • The zygote produces somatic cells by mitosis, and develops into an adult.

Animal Life Cycles

  • Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism.
  • Only diploid cells can undergo meiosis.
  • The halving and doubling of chromosomes contributes to genetic variation in offspring.

Meiosis

  • Meiosis reduces the number of chromosome sets from diploid (2n) to haploid (n).
  • Meiosis is preceded by replication of chromosomes
  • Meiosis takes place in two consecutive cell divisions: meiosis I and meiosis II.
  • Meiosis I involves separation of homologous chromosomes.
  • Meiosis II involves separation of sister chromatids.
  • The two cell divisions result in four haploid daughter cells, rather than the two daughter cells in mitosis.
  • Each daughter cell has only half as many chromosomes as the parent cell.
  • Crossover allows for genetic recombination.

Comparing Mitosis and Meiosis

  • Mitosis:
  • Conserves the number of chromosome sets.
  • Produces cells that are genetically identical to the parent cell.
  • Meiosis:
  • Reduces the number of chromosomes sets from two (diploid) to one (haploid).
  • Produces cells that differ genetically from each other and from the parent cell.

Events Unique to Meiosis I

  • Synapsis: The pairing of homologous chromosomes followed by crossing over.
  • Crossing over: Exchange of genetic material between homologous chromosomes.
  • Homologous pairs at the metaphase plate
  • Separation of homologs during anaphase I

Meiosis I Separates Homologues

  • Two consecutive cell divisions = four haploid daughter cells
  • Synapsis and crossing over
  • Homologous pairs at metaphase plate
  • Separation of homologs

Meiosis II Separates Sister Chromatids

  • Very similar to mitosis.
  • Sister chromatids separate during anaphase II.
  • Four haploid daughter cells result

Results of Meiosis

  • Chromosomes duplicate before meiosis.
  • Pairs of homologs and crossover at chiasma allows for genetic recombination.
  • The chromatids are sorted into four haploid daughter cells.

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