Chromosomes: the cellular basis of the instructions Mitosis Meiosis

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Chromosomes the cellular basis of the
instructionsMitosis - Meiosis
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• Diploid organism two sets of chromosomes ( one
  from each parent)
• 2n
• Haploid organism one set of chromosomes
• n

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• Germ cells the cells that provide the continuity
  of life from generation to the next

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• Somatic cells all the others

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n
n
2n
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Mitosis
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The cell cycle
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2C
4C
4C
2C
2C
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Mitosis Sister chromatids separate at anaphase
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Diploid cells
2C
4C
4C
Homologous chromatids
2C
2C
Diploid cells
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Meiosis
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2N
2C
Prophase I
2N
4C
2N
4C
2N
4C
1N
2C
1N
2C
1N
1C
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Prophase I
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Meiosis anaphase I Homologous chromosomes
separate Reduction from diploid to haploid
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Meiosis 1st division reduction from diploid to
haploid number of chromosomestwo haploid cells
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Meiosis 2nd division like mitosis with haploid
set
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Meiosis begins by replicating the chromosomes
This step is identical to mitosis
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The homologous chromosomes then pairs
Centromeres Do not split At meiosis I
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2n 2C
2n 4C
Centromeres Do not split At meiosis I
2n 4C
Meiosis I is reductional
n 2C
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Centromeres Do split At meiosis II
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Meiosis 1st division reduction from diploid to
haploid number of chromosomestwo haploid cells
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MITOSIS
Somatic cells
2n
1 cell division 2 daughter cells
2n
2n
MEIOSIS
Cells in sexual cycle
2 cell divisions 4 product of meiosis
n
n
2n
n
n
nchromosome number
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Mitosis Conservative process Daughter cells
genotypes identical to parental genotypes
Meiosis Promotes variation among the product of
meiosis (crossing over)
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I
II
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X Bearing sperm
egg
ZYGOTE
2n
2n
2n
Mitoses
Growth and differentiation of organs and tissues
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
2n
Somatic cells
Female germ line
2n
2n
2n
Proliferation of gonial cells
2n
2n
oogonia
2n
2n
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Primary oocytes
2n
Meiosis I
Secondary oocytes Polar body
Meiosis II
fertilization
n
Egg 3 polar bodies
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Female meiosis

• Birth diplotene of prophase I
• At puberty every month
• maturation progress to metaphase II, release
  from the ovary
• Penetration of the sperm
• continue to anaphase II

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Final result
Mitosis two genetically identical diploid cells
from one diploid parent cell
 
Meiosis Four genetically different haploid
cells from one diploid parent cell