Cell Division: Mitosis and Meiosis

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Questions and Answers

What is the definition of mitosis?

Cell division in which the nucleus divides into nuclei containing the same number of chromosomes. Two daughter cells identical to the parent. Takes 2 to 4 hours and is constant. Segregation of sister chromatids. Growth of the embryo and in somatic cells capable of cell division. Processes include prophase, metaphase, anaphase, telophase, and cytokinesis.

What is the definition of nondisjunction?

An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.

What is meant by the cell cycle?

The time from the birth of a new somatic cell until it divides into two new daughter cells.

What is interphase in the cell cycle?

<p>The period between cell division, which includes G1, S, and G2 phases.</p> Signup and view all the answers

What is the spindle assembly checkpoint?

<p>A checkpoint that ensures all chromosomes are properly attached to the spindle fibers before they can segregate.</p> Signup and view all the answers

What is the G1 checkpoint?

<p>A checkpoint that checks for cell size, nutrients, growth factors, and DNA damage.</p> Signup and view all the answers

What happens during the G0 phase?

<p>Cells that have left the cell cycle and are not dividing.</p> Signup and view all the answers

What does the G2 checkpoint check for?

<p>Cell size and DNA replication.</p> Signup and view all the answers

What is the correct order of the interphase stages?

<p>G1, S, G2, M (B)</p> Signup and view all the answers

What is the G1 phase?

<p>The first stage in interphase, during which cellular growth and development take place. Cell size increases and checks to see if the cell is ready for division.</p> Signup and view all the answers

What occurs during the S phase of interphase?

<p>The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated. Two sister chromatids per chromosome (2n; 4d). DNA synthesis/DNA replication. Enzymes of replication are active. DNA proofreading activity of DNA polymerase is active.</p> Signup and view all the answers

What phases are included in the M phase?

<p>Mitosis and cytokinesis.</p> Signup and view all the answers

What is the result of cytokinesis?

<p>Two daughter cells each with 2n; 2d.</p> Signup and view all the answers

What is the role of p53 in the cell cycle?

<p>If there is something wrong with the cell, it is a checkpoint that regulates cells through the cell cycle. Only two in the human body.</p> Signup and view all the answers

What are the consequences of increased p53 protein levels after DNA damage? (Select all that apply)

<p>May cause apoptosis if the damage is extensive (B), Activates DNA repair systems (C), Cell cycle arrest or activation of G1-S checkpoint (D)</p> Signup and view all the answers

What are the consequences of loss of p53 tumor suppressor activity?

<p>Allows proliferation of cells with DNA damage. Uncontrolled proliferation can lead to tumor development.</p> Signup and view all the answers

What happens during prophase?

<p>The beginning of mitosis. The nuclear envelope dissolves. The mitotic spindle forms (tubulin). Chromosomes condense and become visible. Chromosomes bind to the spindle. Homologous chromosomes and sister chromatids are present.</p> Signup and view all the answers

What are homologous chromosomes?

<p>Chromosomes that have the same sequence of genes and the same structure.</p> Signup and view all the answers

What are sister chromatids?

<p>Identical copies of a chromosome; full sets of these are created during the S subphase of interphase.</p> Signup and view all the answers

What happens during mitotic nondisjunction during embryogenesis?

<p>After fertilization (embryogenesis). The sister chromatids of a chromosome fail to separate (aneuploidy in daughter cells). The fetus is a mosaic. Karyotype shows a mixture of cells; normal cells, and cells with aneuploidy.</p> Signup and view all the answers

What can mitotic nondisjunction during embryogenesis lead to?

<p>Normal karyotype and cells with trisomy 21.</p> Signup and view all the answers

What is mosaicism?

<p>A condition in which cells within the same person have a different genetic makeup. Karyotype shows a mixture of normal and aneuploidy cells. Confined germline mosaic.</p> Signup and view all the answers

What happens during meiosis in males?

<p>Forms four gametes, each has 23 chromosomes. One of each kind of autosome and either an X or a Y (23X or 23Y).</p> Signup and view all the answers

What is the result of meiosis in females?

<p>Results in the formation of one ovum (23X) and polar bodies.</p> Signup and view all the answers

What is spermatogenesis?

<p>Formation of sperm.</p> Signup and view all the answers

What is oogenesis?

<p>The production, growth, and maturation of an egg, or ovum.</p> Signup and view all the answers

What happens during meiosis I?

<p>Homologous chromosomes separate (reduction division). (n; 2d)</p> Signup and view all the answers

What does crossing over ensure?

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

What are the crucial roles of meiosis? (Select all that apply)

<p>Formation of haploid gametes (n) (B), Genetic recombination and diversity (C)</p> Signup and view all the answers

What happens during non-disjunction in Meiosis I?

<p>Homologous chromosomes fail to separate. Result in n + 1, n + 1, n - 1, n - 1.</p> Signup and view all the answers

Describe non-disjunction in Meiosis II.

<p>Sister chromatids fail to separate. Result in n, n, n+1, n-1.</p> Signup and view all the answers

What are the effects of nondisjunction during meiosis?

<p>Increased maternal age increases meiotic nondisjunction risk. May occur in meiosis I or II. Aneuploidy. Karyotype shows ALL cells with an abnormal karyotype. Differentiated from mitotic nondisjunction.</p> Signup and view all the answers

What is monosomy?

<p>Chromosomal abnormality consisting of the absence of one chromosome from the normal diploid number. Only compatible with X (Turner Syndrome).</p> Signup and view all the answers

What is Turner Syndrome?

<p>A chromosomal disorder in females in which either an X chromosome is missing, making the person XO instead of XX, or part of one X chromosome is deleted.</p> Signup and view all the answers

What are the origins of a pair of homologous chromosomes?

<p>One copy is derived from the dad, and a second copy is derived from the mom.</p> Signup and view all the answers

What is maternal uniparental disomy?

<p>Inheritance of both chromosome copies from the mother. No dad copy.</p> Signup and view all the answers

Define paternal uniparental disomy.

<p>Inheritance of both chromosome copies from the father. No mom copy.</p> Signup and view all the answers

Describe a paternally imprinted gene.

<p>Transcriptionally silenced if it was transmitted from the father.</p> Signup and view all the answers

What is a maternally imprinted gene?

<p>Transcriptionally silenced if it was transmitted from the mother; paternally inherited allele is expressed.</p> Signup and view all the answers

What is notable about chromosome?

<p>Prader-Willi syndrome, Angelman syndrome, Marfan syndrome.</p> Signup and view all the answers

What does Me-Si stand for?

<p>Methylated, it's Silenced.</p> Signup and view all the answers

What happens during Meiosis 1: sex chromosome nondisjunction in males?

<p>The X and Y chromosomes fail to separate properly during meiosis I. This will result in sperm cells with either two copies of the X chromosome, two copies of the Y chromosome, or no sex chromosomes. The other sperm cells will have one copy of the sex chromosome.</p> Signup and view all the answers

Describe the effects on a zygote produced from Meiosis 1: sex chromosome nondisjunction in males.

<p>The resulting zygote can have either an extra X chromosome or an extra Y chromosome, or may have an X or a Y chromosome missing. This can lead to conditions like Klinefelter Syndrome which is XXY or Turner's syndrome, which is XO.</p> Signup and view all the answers

Describe what happens during Meiosis and non-disjunction of the X chromosome in an ovum.

<p>This could lead to the formation of an egg cell with two X chromosomes or an egg cell with no X chromosomes.</p> Signup and view all the answers

How many sperm cells are produced per round of male meiosis?

<p>Four.</p> Signup and view all the answers

What is the outcome of female meiosis?

<p>One egg and three polar bodies.</p> Signup and view all the answers

When do mitotic divisions of cells occur in males and females?

<p>Mitotic divisions of cells occur at different times in males and females. All mitotic divisions for females are completed by birth.</p> Signup and view all the answers

Describe the timeline of gametogenesis in females.

<p>At birth, the primary oocytes are arrested at prophase 1 of meiosis 1 (frozen eggs). Meiosis II is only completed after fertilization.</p> Signup and view all the answers

Give a brief description of male gametogenesis.

<p>Male gametogenesis, or spermatogenesis, commences at puberty. There are 30 to 500 mitotic divisions in gamete formation, producing four spermatids per meiosis. A male produces 100 to 200 million sperm cells per ejaculate.</p> Signup and view all the answers

What is the process of female gametogenesis?

<p>Early embryonic life, 20 to 30 mitotic divisions in gamete formation. One ovum (polar bodies) per meiosis for gamete production. One ovum per menstrual cycle for gamete production.</p> Signup and view all the answers

What are the defects if maternal or paternal age is increased?

<p>There is a higher risk of non-disjunction during meiotic divisions I or II in a female greater than 35 years, resulting in a higher risk of trisomy in the fetus. The higher the paternal age, the greater the risk of development of new dominant single-gene mutations (replication error).</p> Signup and view all the answers

What are the symptoms of Klinefelter Syndrome (XXY)?

<p>Underdeveloped sex organs, breast development, large hands, and long arms and legs. Extra X chromosome.</p> Signup and view all the answers

At the beginning of meiosis, how many chromosomes and sister chromatids are present?

<p>There are 46 chromosomes and 92 sister chromatids.</p> Signup and view all the answers

How many chromosomes and sister chromatids are present at the end of meiosis I?

<p>Each cell has 23 chromosomes and 46 sister chromatids.</p> Signup and view all the answers

How many chromosomes and chromatids are present at the end of meiosis II?

<p>There are 23 chromosomes and 23 chromatids.</p> Signup and view all the answers

Flashcards

Mitosis

Cell division in which the nucleus divides into nuclei containing the same number of chromosomes. Two daughter cells identical to the parent. 2 to 4 hours and is constant. Segregation of sister chromatids. Growth of embryo and in somatic cells capable of cell division. Prophase, metaphase, anaphase, telophase, and cytokinesis.

Meiosis

A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Nondisjunction

An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.

Cell cycle

Time from birth of a new somatic cell until it divides to two new daughter cells. Interphase (period between cell division) and mitosis (period of actual cell division).

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Interphase

Time between cell division. G1, S, and G2.

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Spindle assembly checkpoint

Check for chromosome attachment to the spindle.

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G1 checkpoint

Check for cell size, nutrients, growth factors, and DNA damage.

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Resting state

G0

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G2 checkpoint

Checks for cell size and DNA replication.

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Interphase stages in order

G1, S, G2, M

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G0 phase

A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.

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G1 stage

First stage in interphase, during which cellular growth and development takes place. Cell size increases. Checks whether ready for division.

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S phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated. TWO SISTER CHROMATIDS PER CHROMOSOME (2n; 4d). DNA synthesis/DNA replication. Enzymes of replication are active. DNA proofreading activity of DNA polymerase is active.

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G2 phase

One large cell with TWO SISTER CHROMATIDS PER CHROMOSOME (2n; 4d). Cell ready for division. DNA content is double (2n; 4d). Cell/cytosol size increase. Post replication DNA repair mechanism active.

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M phase

Includes mitosis and cytokinesis. New cell enters the cycle.

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After cytokinesis...

There are two daughter cells at the end. 2n;2d

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Role of p53 in cell cycle

If there is something wrong with the cell, it is a checkpoint that regulates cells through the cell cycle. Only 2 in the human body.

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DNA damage results increased level of p53 protein which causes:

1.) Cell cycle arrest or activation of G1-S checkpoint. 2.) Activates DNA repair systems. 3.) If damage is extensive, may cause apoptosis.

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Loss of p53 tumor suppressor activity

Allows proliferation of cells with DNA damage. Uncontrolled proliferation can lead to tumor development.

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Prophase

Beginning of mitosis. Nuclear envelope dissolves. Mitotic spindle forms (tubulin). Chromosomes condense and visible. Chromosomes bind to spindle. Homologous chromosomes and sister chromatids.

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Homologous chromosomes

Chromosomes that have the same sequence of genes and the same structure.

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Sister chromatids

Identical copies of a chromosome. Full sets of these are created during the S subphase of interphase.

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Metaphase

Chromosomes condense and maximally visible. Align up the middle. Visualized by karyotyping. Microtubules attach to centromere kinetochores.

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Anaphase

Sister chromatids move to centrioles. Separation of sister chromatids. Non-disjunction during anaphase is mitotic non-disjunction.

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Telophase

Sister chromatids move to opposite poles. Nuclear envelope starts forming. Chromosomes less condensed. Two new daughter cells (cytokinesis). Daughter cells have the same genetic composition as the parent cell (2n; 46 chromosomes; 23 pairs of chromosomes; 2d).

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Study Notes

Mitosis

  • Cell division resulting in two identical daughter cells.
  • Occurs in somatic cells for growth and repair.
  • Takes 2-4 hours.
  • Involves stages: prophase, metaphase, anaphase, telophase, and cytokinesis.
  • Sister chromatids separate during anaphase.

Meiosis

  • Cell division forming four unique haploid gametes.
  • Occurs in gamete-producing cells (ovaries and testes).
  • Produces gametes with half the number of chromosomes as the parent cell (haploid).
  • Genetic variation achieved through crossing over and random alignment.
  • Two phases: Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate).

Nondisjunction

  • Error in cell division where chromosomes fail to separate properly.
  • Can occur during mitosis or meiosis.
  • Results in aneuploidy (abnormal chromosome number) in daughter cells.
  • Can lead to genetic disorders like Down syndrome (trisomy 21).

Cell Cycle

  • Series of events from a cell's formation to its own division.
  • Consists of interphase (G1, S, G2) and mitosis (M).

Interphase

  • Phase between cell divisions.
  • Includes three stages: G1, S, and G2.

G1, S, G2

  • G1: Growth and development; cell monitors size/nutrients before division.
  • S: DNA replication, forming sister chromatids.
  • G2: Checks if DNA replication was accurate and prepares for division.

Checkpoints

  • Spindle assembly checkpoint: Checks chromosome attachment to spindle.
  • G1 checkpoint: Checks for cell size, nutrients, growth factors, and DNA damage.
  • G2 checkpoint: Checks for any errors in DNA replication before mitosis.
  • P53 regulates checkpoints if damaged DNA is found, resulting in halting the cycle to allow repair or apoptosis

G0 Phase

  • Resting state; cells exit the cell cycle and may not divide again.

Mitosis Stages

  • Prophase: Chromosomes condense, nuclear envelope breaks down, spindle forms.
  • Metaphase: Chromosomes align at the cell's equator.
  • Anaphase: Sister chromatids separate and move to opposite poles.
  • Telophase: Chromosomes decondense, nuclear envelope reforms, cytokinesis occurs.

Mitosis Non-Disjunction

  • Occurs during mitotic division (embryogenesis)
  • Results in variable amounts of cells with abnormal chromosome numbers and mixture of normal ones in a fetus
  • Mosaic

Meiotic Non-Disjunction

  • Can happen during Meiosis I or II
  • Results in aneuploidy gametes leading to chromosomal abnormalities in offspring.
  • Higher risk with increasing maternal or paternal age.

Aneuploidy

  • Abnormal number of chromosomes.

Trisomy 21

  • Three copies of chromosome 21, causing Down syndrome.

Mosaicism

  • Mixture of cells with different karyotypes within the same individual.

Gametogenesis (Males and Females)

  • Spermatogenesis (males): Results in four spermatids per round of meiosis (forming haploid sperm).
  • Oogenesis (females): Results in one mature ovum and three polar bodies.
  • Female meiosis starts in the embryo and is arrested at prophase I.

Chromosome Imprinting

  • Genes are expressed differently depending on whether they're inherited from the mother or the father.

Disorders

  • Klinefelter syndrome: Extra X chromosome in males.
  • Turner syndrome: Missing or abnormal X chromosome in females.

Meiosis Stages (Specific)

  • Meiosis I: Homologous chromosomes segregate.
  • Meiosis II: Sister chromatids segregate.
  • Crossing over in prophase I increases genetic variation.

Imprinting (maternal/paternal)

  • Genes function differently based on their parental origin.

Chromosome 15 Imprinting

  • Prader-Willi and Angelman syndromes are linked to the chromosome 15 imprinting errors.

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