Unit 3 meiosis


Published on

Published in: Education, Technology
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Unit 3 meiosis

  1. 1. Campbell & Reece, 2010Chapter 13UNIT 3: MEIOSISREDUCTION DIVISION
  2. 2.  In humans, somatic cells (body cells) have:• 23 pairs of homologous chromosomes and• one member of each pair from each parent. The human sex chromosomes (Gonosomes)X and Y differ in size and genetic composition. The other 22 pairs of chromosomes areautosomes with the same size and geneticcomposition.1. CHROMOSOMES ARE MATCHED INHOMOLOGOUS PAIRS© 2012 Pearson Education, Inc.
  3. 3.  Homologous chromosomes are matched in:• length,• centromere position, and• gene locations (locus). A locus (plural, loci) is the position of a gene. Different versions (alleles) of a gene may befound at the same locus on maternal andpaternal chromosomes.© 2012 Pearson Education, Inc.Centromere
  4. 4.  Homologous chromosome pair© 2012 Pearson Education, Inc.Centromere
  5. 5.  Humans and most animals and plants have diploidbody cells. That means they have two sets of chromosomes(homologous chromosome pair) one from eachparent. Diploid is written 2n. It refers to the total number of chromosomesa cell can have.2. GAMETES HAVE A SINGLE SET OFCHROMOSOMES© 2012 Pearson Education, Inc.
  6. 6.  Meiosis is a process that converts diploidnuclei to haploid nuclei.• Diploid cells have 2 sets of chromosomes.• Haploid cells have 1 set of chromosomes.• Meiosis occurs in the sexorgans, producing gametes—sperm andeggs. Fertilization is the fusion of a sperm and eggcell. The zygote has a diploid chromosomenumber, one set from each parent.© 2012 Pearson Education, Inc.
  7. 7. Haploid gametes (n  23)Egg cellSperm cellFertilizationnnMeiosisOvary TestisDiploidzygote(2n  46)2nMitosisKeyHaploid stage (n)Diploid stage (2n)Multicellular diploidadults (2n  46)A life cycle
  8. 8.  All sexual life cycles include an alternationbetween• a diploid stage and• a haploid stage. Why is meiosis so important? It produceshaploid gametes which prevents thechromosome number from doubling in everygeneration. Produce gametes for fertilization.© 2012 Pearson Education, Inc.
  9. 9. 3 Meiosis is a type of cell division that produceshaploid gametes from diploid cells. Two haploid gametes combine in fertilization torestore the diploid state in the zygote.3. MEIOSIS
  11. 11. MEIOSIS I consisting of 5 phases:Interphase I, Prophase I, MetaphaseI, Anaphase I, Telophase I.MEIOSIS II consisting of 4 phasesProphase II, Metaphase II, AnaphaseII, Telophase II.MEIOSIS HAS 2 STAGES:© 2012 Pearson Education, Inc.
  12. 12. Cell build up energyDNA Replication (to makeduplicated chromosomesCell doesn’t changestructurally.MEIOSIS I : INTERPHASE© 2012 Pearson Education, Inc.
  13. 13. Events occurring in the nucleus:• Chromosomes coil and become individual chromo-somes, nucleolus and nuclear envelope disappear.• Homologous chromosomes come together as pairs bysynapsis forming a tetrad (Each pair, with fourchromatids)• Non-sister chromatids exchange genetic materialthrough the process of crossing over to ensure geneticvariation.• Centrioli move to opposite poles with spindle fibersbetween them.MEIOSIS I : PROPHASE I
  14. 14. MEIOSIS I : PROPHASE I© 2012 Pearson Education, Inc.
  15. 15.  Genetic recombination is the production of newcombinations of genes due to crossing over. Crossing over is an exchange of genesbetweenseparate (non-sister) chromatids on homologouschromosomes.• Non-sister chromatids join at a chiasma(plural, chiasmata), the site of attachment.• Genetic material are exchanged betweenmaternal and paternal (nonsister) chromatids.CROSSING OVER© 2012 Pearson Education, Inc.
  16. 16. CROSSING OVER© 2012 Pearson Education, Inc.
  17. 17.  Centrioli has reached thepoles. Homologous pairs align atthe cell equator. The two chromosomes attachto one spindle fiber by meansof the kinetochore of thecentromere..MEIOSIS I: METAPHASE I© 2012 Pearson Education, Inc.
  18. 18.  Spindle fibers contract. Duplicated chromosomesmove to opposite poles..MEIOSIS I: ANAPHASE I© 2012 Pearson Education, Inc.
  19. 19. • Duplicated chromosomeshave reached the poles.• A nuclear envelope andnucleolus re-forms aroundchromosomes.• Each nucleus now has thehaploid number ofchromosomes.• Cell invaginates forming acleavage furrow, whichextends to for 2 separatehaploid cells.MEIOSIS I: TELOPHASE I© 2012 Pearson Education, Inc.
  20. 20.  Follows meiosis I without chromosomeduplication. Each of the two haploid products entersmeiosis II.MEIOSIS II© 2012 Pearson Education, Inc.
  21. 21. • Chromosomes coil andbecome compact (ifuncoiled after telophase I).• Nuclear envelope andnucleolus, if re-formed, dissappears again.• Centrioli move to oppositepoles, forming spindlefibers between them.MEIOSIS II: PROPHASE II© 2012 Pearson Education, Inc.
  22. 22. • Individual duplicatedchromosomes align on theequator.• One chromosome per spindlefiber attached by means ofkinetochore of centromere.• Centrioli has reached thepoles.MEIOSIS II: METAPHASE II© 2012 Pearson Education, Inc.
  23. 23. • Spindle fibers contract.• Duplicated chromosomessplit in half (centromeredividing in 2)• Daughter chromosomesmove to opposite poles.MEIOSIS II: ANAPHASE II© 2012 Pearson Education, Inc.
  24. 24. • Daughter chromosomes hasreached the poles.• Two cells invaginate and form 4daughter haploid cells(gametes)• They uncoil and formchromatin.• Nuclear envelope andnucleolus for around chromatinagain.• Centrioli for centrosome.MEIOSIS II: TELOPHASE II
  25. 25. SUMMERY OF MEIOSIS IIProphase II Metaphase II Anaphase IIHaploid daughtercells formingTelophase IIand Cytokinesis
  26. 26.  Mitosis and meiosis both• begin with diploid parent cells that• have chromosomes duplicated during theprevious interphase. However the end products differ.• Mitosis produces two genetically identicaldiploid somatic daughter cells.• Meiosis produces four genetically uniquehaploid gametes.4. SIMILARITIES AND DIFFERENCESBETWEEN MITOSIS AND MEIOSIS
  27. 27. • Independent orientation at metaphaseI• Random fertilization.• Crossing over of genes duringprophase I5. GENETIC VARIATION IN GAMETESRESULTS FROM:© 2012 Pearson Education, Inc.
  28. 28. 6. KARYOTYPE© 2012 Pearson Education, Inc.• A karyotype is an ordered display ofmagnified images of an individual’schromosomes arranged in pairs.• Karyotypes allow for the observation of : homologous chromosome pairs, chromosome number, and chromosome structure.
  30. 30. CentromereSisterchromatidsPair ofhomologouschromosomesSex chromosomes
  31. 31.  An extra copy of chromosome 21 causesDown syndrome or also known as TRISOMY21. A. Trisomy 21• involves the inheritance of three copies ofchromosome 21 and• is the most common human chromosomeabnormality.7. ALTERATION IN CHROMOSOME NUMBER© 2012 Pearson Education, Inc.
  32. 32. Down syndrome
  33. 33.  Trisomy 21 produces a characteristic set ofsymptoms, which include:• mental retardation,• characteristic facial features,• short stature,• heart defects,• susceptibility to respiratoryinfections, leukemia, and Alzheimer’s disease, and• shortened life span. The incidence increases with the age of the mother.
  34. 34.  Nondisjunction is the failure of chromosomes orchromatids to separate normally during meiosis. Thiscan happen during:• meiosis I, if both members of a homologous pair goto one pole or• meiosis II if both sister chromatids go to one pole. Fertilization after nondisjunction yields zygotes withaltered numbers of chromosomes.B. ACCIDENTS DURING MEIOSIS CANALTER CHROMOSOME NUMBER
  35. 35. NondisjunctionMEIOSIS IMEIOSIS IINormalmeiosis IIGametesNumber ofchromosomesAbnormal gametesn  1 n  1 n  1 n  1
  36. 36. Normalmeiosis IMEIOSIS IMEIOSIS IINondisjunctionAbnormal gametes Normal gametesn  1 n  1 n n
  37. 37. Sex chromosome abnormalities tend tobe less severe, perhaps because of• the small size of the Y chromosomeor• X-chromosome inactivation.C. ABNORMAL NUMBERS OF SEXCHROMOSOMES© 2012 Pearson Education, Inc.
  38. 38.  In general,• a single Y chromosome is enough to produce“maleness,” even in combination with severalX chromosomes, and• the absence of a Y chromosome yields“femaleness.”© 2012 Pearson Education, Inc.
  39. 39.  The following table lists the most common human sexchromosome abnormalities.© 2012 Pearson Education, Inc.
  40. 40.  Errors in mitosis or meiosis may producepolyploid species, with more than twochromosome sets. .D. NEW SPECIES CAN ARISE FROMERRORS IN CELL DIVISION© 2012 Pearson Education, Inc.
  41. 41.  Chromosome breakage can lead torearrangements that can produce:• genetic disorders or,• if changes occur in somatic cells, cancer.8. ALTERATIONS OF CHROMOSOMESTRUCTURE© 2012 Pearson Education, Inc.
  42. 42. • a deletion, the loss of a chromosomesegment,• a duplication, the repeat of a chromosomesegment,• an inversion, the reversal of a chromosomesegment, or• a translocation, the attachment of a segmentto a nonhomologous chromosome that can bereciprocal.THESE REARRANGEMENTS MAY INCLUDE:
  43. 43. THESE REARRANGEMENTS MAY INCLUDE:© 2012 Pearson Education, Inc.DeletionDuplicationInversionReciprocal translocationHomologouschromosomes Nonhomologouschromosomes