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Campbell & Reece, 2010
Chapter 13
UNIT 3: MEIOSIS
REDUCTION DIVISION
 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 are
autosomes with the same size and genetic
composition.
1. CHROMOSOMES ARE MATCHED IN
HOMOLOGOUS PAIRS
© 2012 Pearson Education, Inc.
 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 be
found at the same locus on maternal and
paternal chromosomes.
© 2012 Pearson Education, Inc.
Centromere
 Homologous chromosome pair
© 2012 Pearson Education, Inc.
Centromere
 Humans and most animals and plants have diploid
body cells.
 That means they have two sets of chromosomes
(homologous chromosome pair) one from each
parent.
 Diploid is written 2n.
 It refers to the total number of chromosomes
a cell can have.
2. GAMETES HAVE A SINGLE SET OF
CHROMOSOMES
© 2012 Pearson Education, Inc.
 Meiosis is a process that converts diploid
nuclei to haploid nuclei.
• Diploid cells have 2 sets of chromosomes.
• Haploid cells have 1 set of chromosomes.
• Meiosis occurs in the sex organs,
producing gametes—sperm and eggs.
 Fertilization is the fusion of a sperm and egg
cell.
 The zygote has a diploid chromosome
number, one set from each parent.
© 2012 Pearson Education, Inc.
Haploid gametes (n  23)
Egg cell
Sperm cell
Fertilization
n
n
Meiosis
Ovary Testis
Diploid
zygote
(2n  46)
2n
Mitosis
Key
Haploid stage (n)
Diploid stage (2n)
Multicellular diploid
adults (2n  46)
A life cycle
 All sexual life cycles include an alternation
between
• a diploid stage and
• a haploid stage.
 Why is meiosis so important? It produces
haploid gametes which prevents the
chromosome number from doubling in every
generation. Produce gametes for fertilization.
© 2012 Pearson Education, Inc.
3
 Meiosis is a type of cell division that produces
haploid gametes from diploid cells.
 Two haploid gametes combine in fertilization to
restore the diploid state in the zygote.
3. MEIOSIS
3
SUMMERY OF THE MEIOSIS PROCESS
MEIOSIS I consisting of 5 phases:
Interphase I, Prophase I, Metaphase I,
Anaphase I, Telophase I.
MEIOSIS II consisting of 4 phases
Prophase II, Metaphase II, Anaphase II,
Telophase II.
MEIOSIS HAS 2 STAGES:
© 2012 Pearson Education, Inc.
Cell build up energy
DNA Replication (to make
duplicated chromosomes
Cell doesn’t change
structurally.
MEIOSIS I : INTERPHASE
© 2012 Pearson Education, Inc.
Events occurring in the nucleus:
• Chromosomes coil and become individual chromo-
somes, nucleolus and nuclear envelope disappear.
• Homologous chromosomes come together as pairs by
synapsis forming a tetrad (Each pair, with four
chromatids)
• Non-sister chromatids exchange genetic material
through the process of crossing over to ensure genetic
variation.
• Centrioli move to opposite poles with spindle fibers
between them.
MEIOSIS I : PROPHASE I
MEIOSIS I : PROPHASE I
© 2012 Pearson Education, Inc.
 Genetic recombination is the production of new
combinations of genes due to crossing over.
 Crossing over is an exchange of genesbetween
separate (non-sister) chromatids on homologous
chromosomes.
• Non-sister chromatids join at a chiasma
(plural, chiasmata), the site of attachment.
• Genetic material are exchanged between
maternal and paternal (nonsister) chromatids.
CROSSING OVER
© 2012 Pearson Education, Inc.
CROSSING OVER
© 2012 Pearson Education, Inc.
 Centrioli has reached the
poles.
 Homologous pairs align at
the cell equator.
 The two chromosomes attach
to one spindle fiber by means
of the kinetochore of the
centromere.
.
MEIOSIS I: METAPHASE I
© 2012 Pearson Education, Inc.
 Spindle fibers contract.
 Duplicated chromosomes
move to opposite poles.
.
MEIOSIS I: ANAPHASE I
© 2012 Pearson Education, Inc.
• Duplicated chromosomes
have reached the poles.
• A nuclear envelope and
nucleolus re-forms around
chromosomes.
• Each nucleus now has the
haploid number of
chromosomes.
• Cell invaginates forming a
cleavage furrow, which
extends to for 2 separate
haploid cells.
MEIOSIS I: TELOPHASE I
© 2012 Pearson Education, Inc.
 Follows meiosis I without chromosome
duplication.
 Each of the two haploid products enters
meiosis II.
MEIOSIS II
© 2012 Pearson Education, Inc.
• Chromosomes coil and
become compact (if
uncoiled after telophase I).
• Nuclear envelope and
nucleolus, if re-formed,
dissappears again.
• Centrioli move to opposite
poles, forming spindle
fibers between them.
MEIOSIS II: PROPHASE II
© 2012 Pearson Education, Inc.
• Individual duplicated
chromosomes align on the
equator.
• One chromosome per spindle
fiber attached by means of
kinetochore of centromere.
• Centrioli has reached the
poles.
MEIOSIS II: METAPHASE II
© 2012 Pearson Education, Inc.
• Spindle fibers contract.
• Duplicated chromosomes
split in half (centromere
dividing in 2)
• Daughter chromosomes
move to opposite poles.
MEIOSIS II: ANAPHASE II
© 2012 Pearson Education, Inc.
• Daughter chromosomes has
reached the poles.
• Two cells invaginate and form 4
daughter haploid cells
(gametes)
• They uncoil and form
chromatin.
• Nuclear envelope and
nucleolus for around chromatin
again.
• Centrioli for centrosome.
MEIOSIS II: TELOPHASE II
SUMMERY OF MEIOSIS II
Prophase II Metaphase II Anaphase II
Haploid daughter
cells forming
Telophase II
and Cytokinesis
 Mitosis and meiosis both
• begin with diploid parent cells that
• have chromosomes duplicated during the
previous interphase.
 However the end products differ.
• Mitosis produces two genetically identical
diploid somatic daughter cells.
• Meiosis produces four genetically unique
haploid gametes.
4. SIMILARITIES AND DIFFERENCES
BETWEEN MITOSIS AND MEIOSIS
• Independent orientation at metaphase
I
• Random fertilization.
• Crossing over of genes during
prophase I
5. GENETIC VARIATION IN GAMETES
RESULTS FROM:
© 2012 Pearson Education, Inc.
6. KARYOTYPE
© 2012 Pearson Education, Inc.
• A karyotype is an ordered display of
magnified images of an individual’s
chromosomes arranged in pairs.
• Karyotypes allow for the observation of :
 homologous chromosome pairs,
 chromosome number, and
 chromosome structure.
SCIENTIST OBSERVING A HUMAN
KARYOTYPE
Centromere
Sister
chromatids
Pair of
homologous
chromosomes
Sex chromosomes
 An extra copy of chromosome 21 causes
Down syndrome or also known as TRISOMY
21.
 A. Trisomy 21
• involves the inheritance of three copies of
chromosome 21 and
• is the most common human chromosome
abnormality.
7. ALTERATION IN CHROMOSOME NUMBER
© 2012 Pearson Education, Inc.
Down syndrome
 Trisomy 21 produces a characteristic set of symptoms,
which include:
• mental retardation,
• characteristic facial features,
• short stature,
• heart defects,
• susceptibility to respiratory infections, leukemia,
and Alzheimer’s disease, and
• shortened life span.
 The incidence increases with the age of the mother.
 Nondisjunction is the failure of chromosomes or
chromatids to separate normally during meiosis. This
can happen during:
• meiosis I, if both members of a homologous pair go
to one pole or
• meiosis II if both sister chromatids go to one pole.
 Fertilization after nondisjunction yields zygotes with
altered numbers of chromosomes.
B. ACCIDENTS DURING MEIOSIS CAN
ALTER CHROMOSOME NUMBER
Nondisjunction
MEIOSIS I
MEIOSIS II
Normal
meiosis II
Gametes
Number of
chromosomes
Abnormal gametes
n  1 n  1 n  1 n  1
Normal
meiosis I
MEIOSIS I
MEIOSIS II
Nondisjunction
Abnormal gametes Normal gametes
n  1 n  1 n n
Sex chromosome abnormalities tend to
be less severe, perhaps because of
• the small size of the Y chromosome
or
• X-chromosome inactivation.
C. ABNORMAL NUMBERS OF SEX
CHROMOSOMES
© 2012 Pearson Education, Inc.
 In general,
• a single Y chromosome is enough to produce
“maleness,” even in combination with several
X chromosomes, and
• the absence of a Y chromosome yields
“femaleness.”
© 2012 Pearson Education, Inc.
 The following table lists the most common human sex
chromosome abnormalities.
© 2012 Pearson Education, Inc.
 Errors in mitosis or meiosis may produce
polyploid species, with more than two
chromosome sets.
 .
D. NEW SPECIES CAN ARISE FROM
ERRORS IN CELL DIVISION
© 2012 Pearson Education, Inc.
 Chromosome breakage can lead to
rearrangements that can produce:
• genetic disorders or,
• if changes occur in somatic cells, cancer.
8. ALTERATIONS OF CHROMOSOME
STRUCTURE
© 2012 Pearson Education, Inc.
• a deletion, the loss of a chromosome
segment,
• a duplication, the repeat of a chromosome
segment,
• an inversion, the reversal of a chromosome
segment, or
• a translocation, the attachment of a segment
to a nonhomologous chromosome that can be
reciprocal.
THESE REARRANGEMENTS MAY INCLUDE:
THESE REARRANGEMENTS MAY INCLUDE:
© 2012 Pearson Education, Inc.
Deletion
Duplication
Inversion
Reciprocal translocation
Homologous
chromosomes Nonhomologous
chromosomes

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Unit 3 meiosis

  • 1. Campbell & Reece, 2010 Chapter 13 UNIT 3: MEIOSIS REDUCTION DIVISION
  • 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 are autosomes with the same size and genetic composition. 1. CHROMOSOMES ARE MATCHED IN HOMOLOGOUS PAIRS © 2012 Pearson Education, Inc.
  • 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 be found at the same locus on maternal and paternal chromosomes. © 2012 Pearson Education, Inc. Centromere
  • 4.  Homologous chromosome pair © 2012 Pearson Education, Inc. Centromere
  • 5.  Humans and most animals and plants have diploid body cells.  That means they have two sets of chromosomes (homologous chromosome pair) one from each parent.  Diploid is written 2n.  It refers to the total number of chromosomes a cell can have. 2. GAMETES HAVE A SINGLE SET OF CHROMOSOMES © 2012 Pearson Education, Inc.
  • 6.  Meiosis is a process that converts diploid nuclei to haploid nuclei. • Diploid cells have 2 sets of chromosomes. • Haploid cells have 1 set of chromosomes. • Meiosis occurs in the sex organs, producing gametes—sperm and eggs.  Fertilization is the fusion of a sperm and egg cell.  The zygote has a diploid chromosome number, one set from each parent. © 2012 Pearson Education, Inc.
  • 7. Haploid gametes (n  23) Egg cell Sperm cell Fertilization n n Meiosis Ovary Testis Diploid zygote (2n  46) 2n Mitosis Key Haploid stage (n) Diploid stage (2n) Multicellular diploid adults (2n  46) A life cycle
  • 8.  All sexual life cycles include an alternation between • a diploid stage and • a haploid stage.  Why is meiosis so important? It produces haploid gametes which prevents the chromosome number from doubling in every generation. Produce gametes for fertilization. © 2012 Pearson Education, Inc.
  • 9. 3  Meiosis is a type of cell division that produces haploid gametes from diploid cells.  Two haploid gametes combine in fertilization to restore the diploid state in the zygote. 3. MEIOSIS
  • 10. 3 SUMMERY OF THE MEIOSIS PROCESS
  • 11. MEIOSIS I consisting of 5 phases: Interphase I, Prophase I, Metaphase I, Anaphase I, Telophase I. MEIOSIS II consisting of 4 phases Prophase II, Metaphase II, Anaphase II, Telophase II. MEIOSIS HAS 2 STAGES: © 2012 Pearson Education, Inc.
  • 12. Cell build up energy DNA Replication (to make duplicated chromosomes Cell doesn’t change structurally. MEIOSIS I : INTERPHASE © 2012 Pearson Education, Inc.
  • 13. Events occurring in the nucleus: • Chromosomes coil and become individual chromo- somes, nucleolus and nuclear envelope disappear. • Homologous chromosomes come together as pairs by synapsis forming a tetrad (Each pair, with four chromatids) • Non-sister chromatids exchange genetic material through the process of crossing over to ensure genetic variation. • Centrioli move to opposite poles with spindle fibers between them. MEIOSIS I : PROPHASE I
  • 14. MEIOSIS I : PROPHASE I © 2012 Pearson Education, Inc.
  • 15.  Genetic recombination is the production of new combinations of genes due to crossing over.  Crossing over is an exchange of genesbetween separate (non-sister) chromatids on homologous chromosomes. • Non-sister chromatids join at a chiasma (plural, chiasmata), the site of attachment. • Genetic material are exchanged between maternal and paternal (nonsister) chromatids. CROSSING OVER © 2012 Pearson Education, Inc.
  • 16. CROSSING OVER © 2012 Pearson Education, Inc.
  • 17.  Centrioli has reached the poles.  Homologous pairs align at the cell equator.  The two chromosomes attach to one spindle fiber by means of the kinetochore of the centromere. . MEIOSIS I: METAPHASE I © 2012 Pearson Education, Inc.
  • 18.  Spindle fibers contract.  Duplicated chromosomes move to opposite poles. . MEIOSIS I: ANAPHASE I © 2012 Pearson Education, Inc.
  • 19. • Duplicated chromosomes have reached the poles. • A nuclear envelope and nucleolus re-forms around chromosomes. • Each nucleus now has the haploid number of chromosomes. • Cell invaginates forming a cleavage furrow, which extends to for 2 separate haploid cells. MEIOSIS I: TELOPHASE I © 2012 Pearson Education, Inc.
  • 20.  Follows meiosis I without chromosome duplication.  Each of the two haploid products enters meiosis II. MEIOSIS II © 2012 Pearson Education, Inc.
  • 21. • Chromosomes coil and become compact (if uncoiled after telophase I). • Nuclear envelope and nucleolus, if re-formed, dissappears again. • Centrioli move to opposite poles, forming spindle fibers between them. MEIOSIS II: PROPHASE II © 2012 Pearson Education, Inc.
  • 22. • Individual duplicated chromosomes align on the equator. • One chromosome per spindle fiber attached by means of kinetochore of centromere. • Centrioli has reached the poles. MEIOSIS II: METAPHASE II © 2012 Pearson Education, Inc.
  • 23. • Spindle fibers contract. • Duplicated chromosomes split in half (centromere dividing in 2) • Daughter chromosomes move to opposite poles. MEIOSIS II: ANAPHASE II © 2012 Pearson Education, Inc.
  • 24. • Daughter chromosomes has reached the poles. • Two cells invaginate and form 4 daughter haploid cells (gametes) • They uncoil and form chromatin. • Nuclear envelope and nucleolus for around chromatin again. • Centrioli for centrosome. MEIOSIS II: TELOPHASE II
  • 25. SUMMERY OF MEIOSIS II Prophase II Metaphase II Anaphase II Haploid daughter cells forming Telophase II and Cytokinesis
  • 26.  Mitosis and meiosis both • begin with diploid parent cells that • have chromosomes duplicated during the previous interphase.  However the end products differ. • Mitosis produces two genetically identical diploid somatic daughter cells. • Meiosis produces four genetically unique haploid gametes. 4. SIMILARITIES AND DIFFERENCES BETWEEN MITOSIS AND MEIOSIS
  • 27. • Independent orientation at metaphase I • Random fertilization. • Crossing over of genes during prophase I 5. GENETIC VARIATION IN GAMETES RESULTS FROM: © 2012 Pearson Education, Inc.
  • 28. 6. KARYOTYPE © 2012 Pearson Education, Inc. • A karyotype is an ordered display of magnified images of an individual’s chromosomes arranged in pairs. • Karyotypes allow for the observation of :  homologous chromosome pairs,  chromosome number, and  chromosome structure.
  • 29. SCIENTIST OBSERVING A HUMAN KARYOTYPE
  • 31.  An extra copy of chromosome 21 causes Down syndrome or also known as TRISOMY 21.  A. Trisomy 21 • involves the inheritance of three copies of chromosome 21 and • is the most common human chromosome abnormality. 7. ALTERATION IN CHROMOSOME NUMBER © 2012 Pearson Education, Inc.
  • 33.  Trisomy 21 produces a characteristic set of symptoms, which include: • mental retardation, • characteristic facial features, • short stature, • heart defects, • susceptibility to respiratory infections, leukemia, and Alzheimer’s disease, and • shortened life span.  The incidence increases with the age of the mother.
  • 34.  Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis. This can happen during: • meiosis I, if both members of a homologous pair go to one pole or • meiosis II if both sister chromatids go to one pole.  Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes. B. ACCIDENTS DURING MEIOSIS CAN ALTER CHROMOSOME NUMBER
  • 35. Nondisjunction MEIOSIS I MEIOSIS II Normal meiosis II Gametes Number of chromosomes Abnormal gametes n  1 n  1 n  1 n  1
  • 36. Normal meiosis I MEIOSIS I MEIOSIS II Nondisjunction Abnormal gametes Normal gametes n  1 n  1 n n
  • 37. Sex chromosome abnormalities tend to be less severe, perhaps because of • the small size of the Y chromosome or • X-chromosome inactivation. C. ABNORMAL NUMBERS OF SEX CHROMOSOMES © 2012 Pearson Education, Inc.
  • 38.  In general, • a single Y chromosome is enough to produce “maleness,” even in combination with several X chromosomes, and • the absence of a Y chromosome yields “femaleness.” © 2012 Pearson Education, Inc.
  • 39.  The following table lists the most common human sex chromosome abnormalities. © 2012 Pearson Education, Inc.
  • 40.  Errors in mitosis or meiosis may produce polyploid species, with more than two chromosome sets.  . D. NEW SPECIES CAN ARISE FROM ERRORS IN CELL DIVISION © 2012 Pearson Education, Inc.
  • 41.  Chromosome breakage can lead to rearrangements that can produce: • genetic disorders or, • if changes occur in somatic cells, cancer. 8. ALTERATIONS OF CHROMOSOME STRUCTURE © 2012 Pearson Education, Inc.
  • 42. • a deletion, the loss of a chromosome segment, • a duplication, the repeat of a chromosome segment, • an inversion, the reversal of a chromosome segment, or • a translocation, the attachment of a segment to a nonhomologous chromosome that can be reciprocal. THESE REARRANGEMENTS MAY INCLUDE:
  • 43. THESE REARRANGEMENTS MAY INCLUDE: © 2012 Pearson Education, Inc. Deletion Duplication Inversion Reciprocal translocation Homologous chromosomes Nonhomologous chromosomes