Meiosis
CHROMOSOMES ARE MATCHED IN
HOMOLOGOUS PAIRS
 In humans, somatic cells (body cells) have:
• 23 pairs of homologous chromos...
HOMOLOGOUS CHROMOSOMES ARE
MATCHED IN:
• length,
• centromere position, and
• gene locations (locus).
 A locus (plural, l...
HOMOLOGOUS CHROMOSOME PAIR
GAMETES HAVE A SINGLE SET OF
CHROMOSOMES
• All organisms have different
numbers of chromosomes.
• A body cell in an adult ...
•These two sets of chromosomes are
homologous.
•Each of the 4 chromosomes that came
from the male parent has a
correspondi...
• A cell that contains both sets of
homologous chromosomes is said to be
diploid.
• The number of chromosomes in a diploid...
DIPLOID
• Di= two sets
• Cell that contains both sets of homologus chromosomes
• Cell contains
• 2 complete sets of chromo...
• The gametes of sexually reproducing
organisms contain only a single set of
chromosomes, and therefore only a single
set ...
HAPLOID
• Means “one set”
• Refers to cells that contain only one set of chromosomes
• Gametes (sex cells)
• Represented b...
WHAT IS MEIOSIS?
• Process of reduction division in which the number of chromosomes per cell
is cut in half through the se...
WHAT HAPENS DURING MEIOSIS?
• Each organism must inherit a single copy of every gene from each of its
“parents.”
• Gametes...
SUMMARY OF MEIOSIS
MEIOSIS HAS TWO STAGES
MEIOSIS I consisting of 5 phases:
Interphase I, Prophase I, Metaphase I, Anaphase I,
Telophase I....
MEIOSIS I
Interphase I Prophase I Metaphase I Anaphase I Telophase I
and
Cytokinesis
INTERPHASE I
Cell build up energy
DNA Replication (to
make duplicated
chromosomes
Cell doesn’t change
structurally.
PROPHASE I
• Each chromosome pairs with its
corresponding homologous
chromosome to form a tetrad.
• There are 4 chromatids...
CROSSING OVER
• When homologous
chromosomes form tetrads in
meiosis I, they exchange
portions of their chromatids
in a pro...
METAPHASE I
 Centrioli has reached the poles.
 Homologous pairs align at the
cell equator.
 The two chromosomes attach ...
ANAPHASE I
• The spindles pull homologous
chromosomes apart to opposite
poles/ends
TELOPHASE I AND CYTOKINESIS
• Duplicated chromosomes have
reached the poles.
• A nuclear envelope and nucleolus re-
forms ...
MEIOSIS II
Meiosis II
• The two cells produced by meiosis I now enter a second
meiotic division.
• Unlike meiosis I, neith...
MEIOSIS II
Telophase I and
Cytokinesis I Prophase II Metaphase II Anaphase II Telophase II
and
Cytokinesis
PROPHASE II
• Chromosomes coil and
become compact (if uncoiled
after telophase I).
• Nuclear envelope and
nucleolus, if re...
METAPHASE II
• Individual duplicated
chromosomes align on the
equator.
• One chromosome per
spindle fiber attached by
mean...
ANAPHASE II
• Spindle fibers contract.
• Duplicated chromosomes
split in half (centromere
dividing in 2)
• Daughter
chromo...
TELOPHASE II AND CYTOKINESIS
• Daughter chromosomes has reached
the poles.
• Two cells invaginate and form 4
daughter hapl...
GAMETE FORMATION
DIFFERENCES BETWEEN MITOSIS ANS
MEIOSIS
MITOSIS MEIOSIS
• Cells produced by mitosis have the
same number of chromosomes an...
ALTERATION IN CHROMOSOME
NUMBER
 An extra copy of chromosome 21 causes Down
syndrome or also known as TRISOMY 21.
 A. Tr...
DOWN SYNDROME
 Trisomy 21 produces a characteristic set of symptoms,
which include:
• mental retardation,
• characteristic facial featu...
Accidents during meiosis can alter
chromosome number
 Nondisjunction is the failure of chromosomes or chromatids to
separ...
Alterations of chromosome structure
Chromosome breakage can lead to
rearrangements that can produce:
• genetic disorders ...
These rearrangements may include:
• a deletion, the loss of a chromosome segment,
• a duplication, the repeat of a chromos...
THANK YOU!!!
REFERENCES
• http://www.slideshare.net/MissMabena/savedfiles?s_title=meiosis-9964891&user_login=anesh95
• Anesh Jeyakumar
...
MEIOSIS
MEIOSIS
MEIOSIS
MEIOSIS
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MEIOSIS

  1. 1. Meiosis
  2. 2. CHROMOSOMES ARE MATCHED IN HOMOLOGOUS PAIRS  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.
  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 be found at the same locus on maternal and paternal chromosomes.
  4. 4. HOMOLOGOUS CHROMOSOME PAIR
  5. 5. GAMETES HAVE A SINGLE SET OF CHROMOSOMES • All organisms have different numbers of chromosomes. • A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent.
  6. 6. •These two sets of chromosomes are homologous. •Each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent.
  7. 7. • A cell that contains both sets of homologous chromosomes is said to be diploid. • The number of chromosomes in a diploid cell is sometimes represented by the symbol 2N. • For Drosophila, the diploid number is 8, which can be written as 2N=8.
  8. 8. DIPLOID • Di= two sets • Cell that contains both sets of homologus chromosomes • Cell contains • 2 complete sets of chromosome • 2 complete sets of genes • Number of chrms in diploid cell represented by 2N • For Drosophilia (fruit fly) 2N=8 • Mendel said: • Each adult cell contains two copies of each gene
  9. 9. • The gametes of sexually reproducing organisms contain only a single set of chromosomes, and therefore only a single set of genes. • These cells are haploid. Haploid cells are represented by the symbol N. • For Drosophila, the haploid number is 4, which can be written as N=4.
  10. 10. HAPLOID • Means “one set” • Refers to cells that contain only one set of chromosomes • Gametes (sex cells) • Represented by N • Drosophilia fruit fly • N=4
  11. 11. WHAT IS MEIOSIS? • Process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell
  12. 12. WHAT HAPENS DURING MEIOSIS? • Each organism must inherit a single copy of every gene from each of its “parents.” • Gametes are formed by a process that separates the two sets of genes so that each gamete ends up with just one set.
  13. 13. SUMMARY OF MEIOSIS
  14. 14. MEIOSIS HAS TWO STAGES 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.
  15. 15. MEIOSIS I Interphase I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis
  16. 16. INTERPHASE I Cell build up energy DNA Replication (to make duplicated chromosomes Cell doesn’t change structurally.
  17. 17. PROPHASE I • Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. • There are 4 chromatids in a tetrad. • Non-sister chromatids exchange genetic material through the process of crossing over to ensure genetic variation. • Centrioli move to opposite poles with spindle fibres between them.
  18. 18. CROSSING OVER • When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over. • Crossing-over produces new combinations of alleles.
  19. 19. METAPHASE I  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. .
  20. 20. ANAPHASE I • The spindles pull homologous chromosomes apart to opposite poles/ends
  21. 21. TELOPHASE I AND CYTOKINESIS • 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.
  22. 22. MEIOSIS II Meiosis II • The two cells produced by meiosis I now enter a second meiotic division. • Unlike meiosis I, neither cell goes through chromosome replication. • Each of the cell’s chromosomes has 2 chromatids.
  23. 23. MEIOSIS II Telophase I and Cytokinesis I Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis
  24. 24. PROPHASE II • Chromosomes coil and become compact (if uncoiled after telophase I). • Nuclear envelope and nucleolus, if re-formed, disappears again. • Centrioli move to opposite poles, forming spindle fibers between them.
  25. 25. METAPHASE II • Individual duplicated chromosomes align on the equator. • One chromosome per spindle fiber attached by means of kinetochore of centromere. • Centrioli has reached the poles.
  26. 26. ANAPHASE II • Spindle fibers contract. • Duplicated chromosomes split in half (centromere dividing in 2) • Daughter chromosomes move to opposite poles.
  27. 27. TELOPHASE II AND CYTOKINESIS • 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.
  28. 28. GAMETE FORMATION
  29. 29. DIFFERENCES BETWEEN MITOSIS ANS MEIOSIS MITOSIS MEIOSIS • Cells produced by mitosis have the same number of chromosomes and alleles as the original cell. • Mitosis allows an organism to grow and replace cells. • Some organisms reproduce asexually by mitosis. ex: coral • Cells produced by meiosis have half the number of chromosomes as the parent cell. • These cells are genetically different from the diploid cell and from each other. • Meiosis is how sexually-reproducing organisms produce gametes.
  30. 30. ALTERATION IN CHROMOSOME NUMBER  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.
  31. 31. DOWN SYNDROME
  32. 32.  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.
  33. 33. Accidents during meiosis can alter chromosome number  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.
  34. 34. Alterations of chromosome structure Chromosome breakage can lead to rearrangements that can produce: • genetic disorders or, • if changes occur in somatic cells, cancer.
  35. 35. These rearrangements may include: • 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 non- homologous chromosome that can be reciprocal.
  36. 36. THANK YOU!!!
  37. 37. REFERENCES • http://www.slideshare.net/MissMabena/savedfiles?s_title=meiosis-9964891&user_login=anesh95 • Anesh Jeyakumar • http://www.slideshare.net/MissMabena/savedfiles?s_title=meiosis-31958724&user_login=mikeu74 • mikeu74 • http://www.slideshare.net/MissMabena/savedfiles?s_title=meiosis-422302&user_login=itamarita1984 • itamarita1984 • http://www.slideshare.net/MissMabena/savedfiles?s_title=10-1-meiosis&user_login=cspavao • cspavao •
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