BioFlix Animations Meiosis Slide Showocw.nthu.edu.tw/ocw/upload/16/306/【L08 輔助資料... · 2012-12-31 · As meiosis begins, a spindle forms and duplicated centrosomes start
Humans produce gametes -- eggs and sperm -- through the process of meiosis.
Cell
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Here we'll follow the production of male gametes by focusing on this cell as it goes through meiosis.
Interphase
Nuclear envelope
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Let’s begin in the nucleus, where genetic information is stored in chromosomes.
Maternal chromosome
Paternal chromosome
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Most of a person's cells are diploid, with two sets of chromosomes. One set is from their mother, shown here in red, and the other set is from their father, shown in blue.
Homologous chromosomes
Paternal chromosome
Maternal chromosome
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Each maternal chromosome has a corresponding paternal chromosome. These matched pairs are called homologous chromosomes.
Duplicating chromosome
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During interphase, chromosomes are duplicated.
Sister chromatids
Maternal chromosome
Sister chromatids
Paternal chromosome
Homologous chromosomes
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Each chromosome now consists of two identical copies called sister chromatids.
DNA Histone proteinsSister chromatids
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Zooming in, we see that each sister chromatid is made up of DNA wound around histone proteins.
DNA Histone proteinsSister chromatids
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Each strand coils up into a tight helical fiber.
Prophase I
Duplicated centrosomes with centriole pairs
Spindle microtubules
Nuclear envelope
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As meiosis begins, a spindle forms and duplicated centrosomes start to migrate toward opposite poles of the cell.
Condensing chromosomes
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Back in the nucleus, the chromosomes are condensing.
Homologous chromosomes
Sister chromatids
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In meiosis, homologous chromosomes stick together in pairs.
Homologous chromosomes
Non-sister chromatids
Sister chromatids
Site of crossing over
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The close association of homologous chromosomes allows segments of non-sister chromatids to trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis.
Spindle microtubules
Nuclear envelope
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After the spindle forms and the nuclear envelope breaks down…
Spindle microtubules
Spindle microtubules
Spindle microtubules
Homologous chromosomes
Centromere
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…microtubules from opposite poles attach to each chromosome of the homologous pair, resulting in a tug-of-war.
Metaphase I
Spindle microtubules
Homologous chromosomes
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At metaphase I, the chromosome pairs are positioned in the middle of the cell.
Anaphase I
Sister chromatids Sister chromatids
Chromosome Chromosome
Paternal genetic material
Maternal genetic material
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The next stage begins when homologous chromosomes separate from each other and move toward opposite poles. Each chromosome still consists of two sister chromatids.
Telophase I & Cytokinesis
Daughter cellDaughter cell
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This cell began meiosis with 46 chromosomes, but each daughter cell now has only 23 chromosomes.
Daughter cellDaughter cell
Meiosis II
Daughter cellSpindle microtubules
Chromosomes
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In meiosis II, microtubules from opposite poles attach to the chromosomes…
Spindle microtubules
Chromosomes
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…which then move to the center of the cell.
Sister chromatids separate
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Next, the sister chromatids separate, becoming full-fledged chromosomes that move to opposite poles.
Daughter cell dividesDaughter cell divides
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Nuclear envelopes re-form, and each daughter cell divides into two cells.
Four haploid cells
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We started with a single diploid cell, and now that meiosis is complete, we have four haploid cells, cells with a single set of chromosomes.
