chromosomes: the cellular basis of the instructions mitosis - meiosis
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Chromosomes: Chromosomes: the cellular basis of the the cellular basis of the
instructionsinstructions
Mitosis - MeiosisMitosis - Meiosis
• Diploid organism: two sets of chromosomes ( one from each parent)
• 2n
• Haploid organism: one set of chromosomes
• n
• Germ cells: the cells that provide the continuity of life from generation to the next
• Somatic cells: all the others
meiosis
Haploid egg Haploid sperm
mitosis
Fertilization
n n
2n
MitosisMitosis
The cell cycle
Prophase
Metaphase Anaphase
Telophase
Interphase
Prophase
Metaphase
Anaphase
Telophase
2N
2N2N
Mitosis2C
4C
4C
2C
2C
Mitosis: Sister chromatids separate at anaphase
Homologous chromatids
Diploid cells
Diploid cells2C
4C
4C
2C
2C
Meiosis
Prophase I
2N 2C
2N 4C
2N 4C
2N 4C
1N 2C
1N 2C
1N 1C
1 .Leptotene
2.Zygotene
3.Pachytene 4.Diplotene 5.Diakinesis
Prophase I
Prophase I
5.Diakinesis4.Diplotene
Crossing overPairing of
homologous chromosomes
Chiasma formation
ChromosomesBreakage and joining
Recombinant chromosomes
Metaphase I Anaphase I
Telophase IProphase II
Prophase I
Meiosis anaphase I :Homologous chromosomes separateReduction from diploid to haploid
Meiosis 1st divisionMeiosis 1st division: : reduction from diploid to haploid reduction from diploid to haploid
number of chromosomesnumber of chromosomes
two haploid cellstwo haploid cells
Meiosis 2Meiosis 2ndnd division: division: like mitosis with haploid setlike mitosis with haploid set
Prophase II
Metaphase II
Anaphase II
Telophase II
4 Haploid cells Gametes4 Haploid cells Gametes
Meiosis begins by replicating the chromosomes
This step is identical to mitosis
The homologous chromosomes then pairs
CentromeresDo not splitAt meiosis I
CentromeresDo not splitAt meiosis I
Meiosis Iis reductional
2n = 2C
2n = 4C
n =2C
2n = 4C
CentromeresDo splitAt meiosis II
Meiosis 1st divisionMeiosis 1st division: : reduction from diploid to haploid reduction from diploid to haploid
number of chromosomesnumber of chromosomes
two haploid cellstwo haploid cells
Crossing over
Homologous chromosomes
Diploid to haploid
Haploid cells
Diploid cells
Homologous chromatids
2n1 cell division: 2 daughter cells
2 cell divisions: 4 product of meiosis
2n
2n
2n
n
n n
n
n=chromosome number
Somatic cellsSomatic cells
Cells in sexual cycleCells in sexual cycle
MITOSISMITOSIS
MEIOSISMEIOSIS
MitosisMitosisConservative process:Conservative process:Daughter cells genotypes identical Daughter cells genotypes identical to parental genotypesto parental genotypes
MeiosisMeiosisPromotes variation among the product Promotes variation among the product of meiosis (crossing over)of meiosis (crossing over)
30 mitotic divisions
4 mitotic divisions
2 meiotic divisions
spermatozoa
spermatids
15 years
Puberty
I
II
2n
2n2n
2n2n 2n2n
2n 2n 2n 2n 2n 2n 2n 2n
2n
2n2n
2n2n 2n2n
egg X Bearing spermZYGOTE
Mitoses
Growth and differentiation of organs and tissues
Somatic cells
Female germ line
Proliferation of gonial cells
oogonia
2n
n
Meiosis I
Meiosis II
Primary oocytes
Secondary oocytesPolar body
Egg + 3 polar bodies
fertilization
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
Final result
Meiosis :Four genetically different haploid cells from one diploid parent cell
Mitosis :two genetically identical diploid cells from one diploid parent cell