1 BIOL 221 BIOL 221 Ch Ch 13 13 Meiosis Meiosis Chromosome number Chromosome number • Human cells ‐ Diploid • 46 total chromosomes per cell • 46 ‐ Diploid number • Humans cells ‐ 23 pairs of homologous chromosomes • 23 ‐ Haploid number • The number of different kinds of chromosomes An Overview of Meiosis An Overview of Meiosis • Human cells are considered diploid because each cell has two copies • Some organisms • Haploid • triploid • tetraploid
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Both mitosis and meiosis are initiated in cells that are diploid or “2n,” meaning cells that contain paired sets ofchromosomes. The members of each pair are homologous– –the same in size and function. Two pairsof homologous chromosomes are shown within the cellsin both the mitosis and meiosis figures. In each homologous pair, one chromosome (in red) comes from the mother of the person whose cell is undergoing meiosis, while the other chromosome (in blue) comes from the father of this person.
Prior to the initiation of both mitosis and meiosis, thechromosomes duplicate. In both processes, eachchromosome is now composed of two sister c hromatids.
In mitosis, the chromosomes line up on the metaphaseplate, one sister chromatid on each side of the plate.In meiosis, homologous chromosomes—not sisterchromatids— l ine up on opposite sides of themetaphase plate.
In mitosis, the sister chromatids separate. In meiosis, thehomologous pairs of chromosomes separate.
The cells divide again, yielding four haploid cells.
somaticcell
duplication duplication
gameteprecursor
Homologousmeans the
same in sizeand function
2n2n
2n2n
2n2n
2n2n
1n2n 1n
1n1n
1n1n 1n1n
2n
homologouspairs
Mitosis Meiosis
In mitosis, cell division takes place, and each of the sisterchromatids from step 4 is now a full-fledged chromosome.Mitosis is finished. In meiosis, one member of eachhomologous pair has gone to one cell, the other memberto the other cell. Because each of these cells now hasonly a single set of chromosomes, each is in the haploidor “1n” state. Next, these single chromosomes line up onthe metaphase plate, with their sister chromatids onopposite sides of the plate.
The sister chromatids of each chromosome then separate.
division division
division division
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2.
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5.
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OverviewofMeiosisOverviewofMeiosis
• Whenthehaploidspermandhaploideggfuse
• adiploidferElizedegg(orzygote)isproduced
• seMngintodevelopmentanewgeneraEonoforganism
TheStepsinMeiosisTheStepsinMeiosis• Meiosis
• oneroundofchromosomeduplicaEon
• followedbytworoundsofcelldivision
• NosecondchromosomeduplicaEonaOerfirstdivision
Both mitosis and meiosis are initiated in cells that are diploid or “2n,” meaning cells that contain paired sets ofchromosomes. The members of each pair are homologous– –the same in size and function. Two pairsof homologous chromosomes are shown within the cellsin both the mitosis and meiosis figures. In each homologous pair, one chromosome (in red) comes from the mother of the person whose cell is undergoing meiosis, while the other chromosome (in blue) comes from the father of this person.
Prior to the initiation of both mitosis and meiosis, thechromosomes duplicate. In both processes, eachchromosome is now composed of two sister c hromatids.
In mitosis, the chromosomes line up on the metaphaseplate, one sister chromatid on each side of the plate.In meiosis, homologous chromosomes—not sisterchromatids— l ine up on opposite sides of themetaphase plate.
In mitosis, the sister chromatids separate. In meiosis, thehomologous pairs of chromosomes separate.
The cells divide again, yielding four haploid cells.
somaticcell
duplication duplication
gameteprecursor
Homologousmeans the
same in sizeand function
2n2n
2n2n
2n2n
2n2n
1n2n 1n
1n1n
1n1n 1n1n
2n
homologouspairs
Mitosis Meiosis
In mitosis, cell division takes place, and each of the sisterchromatids from step 4 is now a full-fledged chromosome.Mitosis is finished. In meiosis, one member of eachhomologous pair has gone to one cell, the other memberto the other cell. Because each of these cells now hasonly a single set of chromosomes, each is in the haploidor “1n” state. Next, these single chromosomes line up onthe metaphase plate, with their sister chromatids onopposite sides of the plate.The sister chromatids of each chromosome then separate.
Both mitosis and meiosis are initiated in cells that are diploid or “2n,” meaning cells that contain paired sets ofchromosomes. The members of each pair are homologous– –the same in size and function. Two pairsof homologous chromosomes are shown within the cellsin both the mitosis and meiosis figures. In each homologous pair, one chromosome (in red) comes from the mother of the person whose cell is undergoing meiosis, while the other chromosome (in blue) comes from the father of this person.
Prior to the initiation of both mitosis and meiosis, thechromosomes duplicate. In both processes, eachchromosome is now composed of two sister c hromatids.
In mitosis, the chromosomes line up on the metaphaseplate, one sister chromatid on each side of the plate.In meiosis, homologous chromosomes—not sisterchromatids— l ine up on opposite sides of themetaphase plate.
In mitosis, the sister chromatids separate. In meiosis, thehomologous pairs of chromosomes separate.
The cells divide again, yielding four haploid cells.
somaticcell
duplication duplication
gameteprecursor
Homologousmeans the
same in sizeand function
2n2n
2n2n
2n2n
2n2n
1n2n 1n
1n1n
1n1n 1n1n
2n
homologouspairs
Mitosis Meiosis
In mitosis, cell division takes place, and each of the sisterchromatids from step 4 is now a full-fledged chromosome.Mitosis is finished. In meiosis, one member of eachhomologous pair has gone to one cell, the other memberto the other cell. Because each of these cells now hasonly a single set of chromosomes, each is in the haploidor “1n” state. Next, these single chromosomes line up onthe metaphase plate, with their sister chromatids onopposite sides of the plate.
The sister chromatids of each chromosome then separate.