meiosis powerpoint presentation
TRANSCRIPT
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GRADE 12: GRADE 12: MEIOSISMEIOSIS
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© 2012 Pearson Education, Inc.
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Why do meiosis?Meiosis is “REDUCTION DIVISION”so Reduces chromosome number, parent cell is 2n while daughter cells are n.
Why do gonosome undergo meiosis?
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Haploid gametes (n 23)
Egg cell
Sperm cell
Fertilization
n
n
Meiosis
Ovary Testis
Diploidzygote(2n 46)
2n
MitosisKey
Haploid stage (n)Diploid stage (2n)
Multicellular diploidadults (2n 46)
A life cycle
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© 2012 Pearson Education, Inc.
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QUIZ TIME…
1. In streptomycin fungus n = 11. What is the diploid number for this species?
2. If a horse egg has 98 chromosomes how many does a horse egg cell have?
3. If n = 16 for goldfish how many chromosome in a fin cell?
4. If 2n = 108 for black spruce trees then what is the haploid number? 2n = 14 for this species. Fill in
the chromosome numbers for each cell.
A
BC
What is process A, B, and C?
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Sex ChromosomesSex Chromosomes
XX chromosome - female XY chromosome - male
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Meiosis I (four phases)Meiosis I (four phases)
• Cell division Cell division that reduces the chromosomechromosome number by one-half.one-half.
• four phasesfour phases:a.a. prophase Iprophase Ib.b. metaphase Imetaphase Ic.c. anaphase Ianaphase Id.d. telophase Itelophase I
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Interphase IInterphase I
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Interphase IInterphase I
nuclear membrane
nucleolus
cell membrane
chromatin
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MEIOSIS I : prophase i
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MEIOSIS I : prophase i
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Metaphase IMetaphase I• Shortest phaseShortest phase
• TetradsTetrads align on the metaphase platemetaphase plate.
• INDEPENDENT ASSORTMENT OCCURS:INDEPENDENT ASSORTMENT OCCURS:1. Orientation of homologous pair to poles is random.2. Variation3. Formula: 2n
Example:Example: 2n = 42n = 4then then n = 2 n = 2
thusthus 2 22 2 = 4 combinations= 4 combinations
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Metaphase IMetaphase I
metaphase plate
OR
metaphase plate
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Anaphase IAnaphase I
• Homologous chromosomes Homologous chromosomes separate and move towards the poles.
• Sister chromatids Sister chromatids remain attached at their centromerescentromeres.
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Anaphase IAnaphase I
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Meiosis i: telophase i
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Meiosis ii
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Meiosis ii: prophase II
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Prophase IIProphase II
• same as prophaseprophase in mitosismitosis
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Metaphase IIMetaphase II
metaphase platemetaphase plate
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Anaphase IIAnaphase II
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Telophase IITelophase II
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Crossing over
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Crossing over
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= Non-separation of chromosomes resulting in diploid or empty gametes.
Non-disjunction
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Downs syndrome = Trisomy 21 - 3 copies of chromosomes 21 equalling a total of 47 chromosomes. = 2n + 1(chance of occurring in oogenesis increases with maternal age)
Turners syndrome = Monosomy X - has only oneone XX chromosomes totalling only 45 chromosomes in her body cells. (monosomy X) = 2n-1
Klinefelter’s syndrome = XXY - male which has an extra Xextra X chromosome = 2n + 1
Conditions caused bynon-disjunction
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A simple check for the presence of a bone in the nose could more accurately test unborn babies for Down's syndrome, scientists say. Researchers say combining the nose test with existing screening methods (amniocentesis, CVS) could lead to a five-fold reduction in the number of miscarriages linked to an invasive procedure used to confirm Down's syndrome.
Down’s syndrome – trisomy 21
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Normal boy who develops some female secondary sex character-istics at puberty.
-slightly lower IQ, infertile, delayed motor, speech, maturation
-treated with testosterone.
Klinefelter’s syndrome XXY
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