Lesson OverviewLesson Overview11.4 Meiosis11.4 Meiosis
Lesson OverviewLesson Overview MeiosisMeiosisTHINK ABOUT ITAs geneticists in the early 1900s appliedMendel’s laws, they wo...
Lesson OverviewLesson Overview MeiosisMeiosisChromosome NumberHow many sets of genes do multicellular organisms inherit?
Lesson OverviewLesson Overview MeiosisMeiosisChromosome NumberHow many sets of genes do multicellular organisms inherit?Th...
Lesson OverviewLesson Overview MeiosisMeiosisChromosome NumberChromosomes—those strands of DNA and protein inside the cell...
Lesson OverviewLesson Overview MeiosisMeiosisDiploid CellsA body cell in an adult fruit fly has eightchromosomes, as shown...
Lesson OverviewLesson Overview MeiosisMeiosisDiploid CellsA cell that contains both sets ofhomologous chromosomes is diplo...
Lesson OverviewLesson Overview MeiosisMeiosisHaploid CellsSome cells contain only a single set of chromosomes, and therefo...
Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?
Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?In prophase I...
Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?During anapha...
Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?As the cells ...
Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisMeiosis is a process in which the number of chromosomes per ...
Lesson OverviewLesson Overview MeiosisMeiosisMeiosis IJust prior to meiosis I, the cell undergoes a round of chromosomerep...
Lesson OverviewLesson Overview MeiosisMeiosisProphase IThe cells begin to divide, and the chromosomes pair up, forming ast...
Lesson OverviewLesson Overview MeiosisMeiosisProphase IAs homologous chromosomes pair up and form tetrads, they undergo ap...
Lesson OverviewLesson Overview MeiosisMeiosisProphase IThen, the crossed sections of the chromatids are exchanged.Crossing...
Lesson OverviewLesson Overview MeiosisMeiosisMetaphase I and Anaphase IAs prophase I ends, a spindle forms and attaches to...
Lesson OverviewLesson Overview MeiosisMeiosisMetaphase I and Anaphase IDuring anaphase I, spindle fibers pull each homolog...
Lesson OverviewLesson Overview MeiosisMeiosisTelophase I and CytokinesisDuring telophase I, a nuclear membrane forms aroun...
Lesson OverviewLesson Overview MeiosisMeiosisMeiosis IMeiosis I results in two cells, calleddaughter cells, each of which ...
Lesson OverviewLesson Overview MeiosisMeiosisMeiosis IIThe two cells produced by meiosis I nowenter a second meiotic divis...
Lesson OverviewLesson Overview MeiosisMeiosisProphase IIAs the cells enter prophase II, theirchromosomes—each consisting o...
Lesson OverviewLesson Overview MeiosisMeiosisMetaphase IIDuring metaphase of meiosis II, chromosomesline up in the center ...
Lesson OverviewLesson Overview MeiosisMeiosisAnaphase IIAs the cell enters anaphase, the pairedchromatids separate.
Lesson OverviewLesson Overview MeiosisMeiosisTelophase II, and CytokinesisIn the example shown here, each of the four daug...
Lesson OverviewLesson Overview MeiosisMeiosisTelophase II, and CytokinesisThese four daughter cells now contain the haploi...
Lesson OverviewLesson Overview MeiosisMeiosisGametes to ZygotesThe haploid cells produced by meiosis II are gametes.In mal...
Lesson OverviewLesson Overview MeiosisMeiosisGametes to ZygotesFertilization—the fusion of male and female gametes—generat...
Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?
Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?In mitosis...
Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?Mitosis do...
Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?Mitosis re...
Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisMitosis is a form of asexual reproduction, where...
Lesson OverviewLesson Overview MeiosisMeiosisReplication and Separation of Genetic MaterialIn mitosis, when the two sets o...
Lesson OverviewLesson Overview MeiosisMeiosisReplication and Separation of Genetic MaterialIn meiosis, homologous chromoso...
Lesson OverviewLesson Overview MeiosisMeiosisReplication and Separation of Genetic MaterialThe sorting and recombination o...
Lesson OverviewLesson Overview MeiosisMeiosisChanges in Chromosome NumberMitosis does not normally change the chromosome n...
Lesson OverviewLesson Overview MeiosisMeiosisChanges in Chromosome NumberA diploid cell that enters mitosis with eight fou...
Lesson OverviewLesson Overview MeiosisMeiosisChanges in Chromosome NumberOn the other hand, a diploid cell that enters mei...
Lesson OverviewLesson Overview MeiosisMeiosisNumber of Cell DivisionsMitosis is a single cell division, resulting in the p...
Lesson OverviewLesson Overview MeiosisMeiosisNumber of Cell DivisionsMeiosis requires two rounds of cell division, and, in...
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CVA Biology I - B10vrv4114

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CVA Biology I - B10vrv4114

  1. 1. Lesson OverviewLesson Overview11.4 Meiosis11.4 Meiosis
  2. 2. Lesson OverviewLesson Overview MeiosisMeiosisTHINK ABOUT ITAs geneticists in the early 1900s appliedMendel’s laws, they wondered where genesmight be located.They expected genes to be carried onstructures inside the cell, but whichstructures?What cellular processes could account forsegregation and independent assortment,as Mendel had described?
  3. 3. Lesson OverviewLesson Overview MeiosisMeiosisChromosome NumberHow many sets of genes do multicellular organisms inherit?
  4. 4. Lesson OverviewLesson Overview MeiosisMeiosisChromosome NumberHow many sets of genes do multicellular organisms inherit?The diploid cells of most adult organisms contain two complete sets ofinherited chromosomes and two complete sets of genes.
  5. 5. Lesson OverviewLesson Overview MeiosisMeiosisChromosome NumberChromosomes—those strands of DNA and protein inside the cell nucleus—are the carriers of genes.The genes are located in specific positions on chromosomes.
  6. 6. Lesson OverviewLesson Overview MeiosisMeiosisDiploid CellsA body cell in an adult fruit fly has eightchromosomes, as shown in the figure.Four of the chromosomes come from itsmale parent, and four come from its femaleparent.These two sets of chromosomes arehomologous, meaning that each of the fourchromosomes from the male parent has acorresponding chromosome from the femaleparent.
  7. 7. Lesson OverviewLesson Overview MeiosisMeiosisDiploid CellsA cell that contains both sets ofhomologous chromosomes is diploid,meaning “two sets.”The diploid number of chromosomes issometimes represented by the symbol 2N.For the fruit fly, the diploid number is 8,which can be written as 2N = 8, where Nrepresents twice the number ofchromosomes in a sperm or egg cell.
  8. 8. Lesson OverviewLesson Overview MeiosisMeiosisHaploid CellsSome cells contain only a single set of chromosomes, and therefore asingle set of genes.Such cells are haploid, meaning “one set.”The gametes of sexually reproducing organisms are haploid.For fruit fly gametes, the haploid number is 4, which can be written asN = 4.
  9. 9. Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?
  10. 10. Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?In prophase I of meiosis, each replicated chromosome pairs with itscorresponding homologous chromosome.During metaphase I of meiosis, paired homologous chromosomes line upacross the center of the cell.
  11. 11. Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?During anaphase I, spindle fibers pull each homologous chromosome pairtoward opposite ends of the cell.In telophase I, a nuclear membrane forms around each cluster ofchromosomes. Cytokinesis follows telophase I, forming two new cells.
  12. 12. Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisWhat events occur during each phase of meiosis?As the cells enter prophase II, their chromosomes—each consisting of twochromatids—become visible.The final four phases of meiosis II are similar to those in meiosis I.However, the result is four haploid daughter cells.
  13. 13. Lesson OverviewLesson Overview MeiosisMeiosisPhases of MeiosisMeiosis is a process in which the number of chromosomes per cell is cutin half through the separation of homologous chromosomes in a diploidcell.Meiosis usually involves two distinct divisions, called meiosis I and meiosisII.By the end of meiosis II, the diploid cell becomes four haploid cells.
  14. 14. Lesson OverviewLesson Overview MeiosisMeiosisMeiosis IJust prior to meiosis I, the cell undergoes a round of chromosomereplication called interphase I.Each replicated chromosome consists of two identical chromatids joined atthe center.
  15. 15. Lesson OverviewLesson Overview MeiosisMeiosisProphase IThe cells begin to divide, and the chromosomes pair up, forming astructure called a tetrad, which contains four chromatids.
  16. 16. Lesson OverviewLesson Overview MeiosisMeiosisProphase IAs homologous chromosomes pair up and form tetrads, they undergo aprocess called crossing-over.First, the chromatids of the homologous chromosomes cross over oneanother.
  17. 17. Lesson OverviewLesson Overview MeiosisMeiosisProphase IThen, the crossed sections of the chromatids are exchanged.Crossing-over is important because it produces new combinations ofalleles in the cell.
  18. 18. Lesson OverviewLesson Overview MeiosisMeiosisMetaphase I and Anaphase IAs prophase I ends, a spindle forms and attaches to each tetrad.During metaphase I of meiosis, paired homologous chromosomes line upacross the center of the cell.
  19. 19. Lesson OverviewLesson Overview MeiosisMeiosisMetaphase I and Anaphase IDuring anaphase I, spindle fibers pull each homologous chromosome pairtoward opposite ends of the cell.When anaphase I is complete, the separated chromosomes cluster atopposite ends of the cell.
  20. 20. Lesson OverviewLesson Overview MeiosisMeiosisTelophase I and CytokinesisDuring telophase I, a nuclear membrane forms around each cluster ofchromosomes.Cytokinesis follows telophase I, forming two new cells.
  21. 21. Lesson OverviewLesson Overview MeiosisMeiosisMeiosis IMeiosis I results in two cells, calleddaughter cells, each of which has fourchromatids, as it would after mitosis.Because each pair of homologouschromosomes was separated, neitherdaughter cell has the two complete setsof chromosomes that it would have in adiploid cell.The two cells produced by meiosis Ihave sets of chromosomes and allelesthat are different from each other andfrom the diploid cell that enteredmeiosis I.
  22. 22. Lesson OverviewLesson Overview MeiosisMeiosisMeiosis IIThe two cells produced by meiosis I nowenter a second meiotic division.Unlike the first division, neither cell goesthrough a round of chromosome replicationbefore entering meiosis II.
  23. 23. Lesson OverviewLesson Overview MeiosisMeiosisProphase IIAs the cells enter prophase II, theirchromosomes—each consisting of twochromatids—become visible.The chromosomes do not pair to formtetrads, because the homologous pairswere already separated during meiosis I.
  24. 24. Lesson OverviewLesson Overview MeiosisMeiosisMetaphase IIDuring metaphase of meiosis II, chromosomesline up in the center of each cell.
  25. 25. Lesson OverviewLesson Overview MeiosisMeiosisAnaphase IIAs the cell enters anaphase, the pairedchromatids separate.
  26. 26. Lesson OverviewLesson Overview MeiosisMeiosisTelophase II, and CytokinesisIn the example shown here, each of the four daughter cells produced inmeiosis II receives two chromatids.
  27. 27. Lesson OverviewLesson Overview MeiosisMeiosisTelophase II, and CytokinesisThese four daughter cells now contain the haploid number (N)—just twochromosomes each.
  28. 28. Lesson OverviewLesson Overview MeiosisMeiosisGametes to ZygotesThe haploid cells produced by meiosis II are gametes.In male animals, these gametes are called sperm. In some plants, pollengrains contain haploid sperm cells.In female animals, generally only one of the cells produced by meiosis isinvolved in reproduction. The female gamete is called an egg in animalsand an egg cell in some plants.
  29. 29. Lesson OverviewLesson Overview MeiosisMeiosisGametes to ZygotesFertilization—the fusion of male and female gametes—generates newcombinations of alleles in a zygote.The zygote undergoes cell division by mitosis and eventually forms a neworganism.
  30. 30. Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?
  31. 31. Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?In mitosis, when the two sets of genetic material separate, each daughtercell receives one complete set of chromosomes. In meiosis, homologouschromosomes line up and then move to separate daughter cells.
  32. 32. Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?Mitosis does not normally change the chromosome number of the originalcell. This is not the case for meiosis, which reduces the chromosomenumber by half.
  33. 33. Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisHow is meiosis different from mitosis?Mitosis results in the production of two genetically identical diploid cells,whereas meiosis produces four genetically different haploid cells.
  34. 34. Lesson OverviewLesson Overview MeiosisMeiosisComparing Meiosis and MitosisMitosis is a form of asexual reproduction, whereas meiosis is an early stepin sexual reproduction.There are three other ways in which these two processes differ.
  35. 35. Lesson OverviewLesson Overview MeiosisMeiosisReplication and Separation of Genetic MaterialIn mitosis, when the two sets of genetic material separate, eachdaughter cell receives one complete set of chromosomes.
  36. 36. Lesson OverviewLesson Overview MeiosisMeiosisReplication and Separation of Genetic MaterialIn meiosis, homologous chromosomes line up and then move to separatedaughter cells.As a result, the two alleles for each gene segregate from each other andend up in different cells.
  37. 37. Lesson OverviewLesson Overview MeiosisMeiosisReplication and Separation of Genetic MaterialThe sorting and recombination of genes in meiosis result in a greatervariety of possible gene combinations than could result from mitosis.
  38. 38. Lesson OverviewLesson Overview MeiosisMeiosisChanges in Chromosome NumberMitosis does not normally change the chromosome number of the originalcell.Meiosis reduces the chromosome number by half.
  39. 39. Lesson OverviewLesson Overview MeiosisMeiosisChanges in Chromosome NumberA diploid cell that enters mitosis with eight four chromosomes willdivide to produce two diploid daughter cells, each of which also haseight four chromosomes.
  40. 40. Lesson OverviewLesson Overview MeiosisMeiosisChanges in Chromosome NumberOn the other hand, a diploid cell that enters meiosis with eight fourchromosomes will pass through two meiotic divisions to produce fourhaploid gamete cells, each with only four two chromosomes.
  41. 41. Lesson OverviewLesson Overview MeiosisMeiosisNumber of Cell DivisionsMitosis is a single cell division, resulting in the production of twogenetically identical diploid daughter cells.
  42. 42. Lesson OverviewLesson Overview MeiosisMeiosisNumber of Cell DivisionsMeiosis requires two rounds of cell division, and, in most organisms,produces a total of four genetically different haploid daughter cells.
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