Meiosis

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Locus

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A gene's location on a particular chromosome

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Asexual reproduction makes . . .

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A clone

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Life cycle

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Generation to generation sequence of stages in the reproductive history of an organism from conception to production of offspring.

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Karyotype

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When images of chromosomes are arranged in pairs

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Homologous chromosomes

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Chromosomes that make up a pair having the same length, centromere position and staining pattern.

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Autosomes

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Don't determine sex

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Syngamy

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Fertilization

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Zygote

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Fertilized egg

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Life cycle of most fungi and some algae

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After gametes fuse to form a diploid zygote meiosis occurs before offspring develop. This meiosis produces not gametes but haploid cells that then divide by mitosis to make a a haploid multicellular adult organism. The haploid organism produces gametes by mitosis. The only diploid stage is the zygote.

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life cycle alternation of generations

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Includes both diploid and haploid multicellular stages.

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Sporophyte

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Multicellular diploid stage of type 3 life cycle. Meiosis in produces haploid cells called spores.

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Spore (concept and product)

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Haploid cell that gives rise to a multicellular individual without fusing with another cell. Spore divides mitotically to generate a multicellular haploid stage called gametophyte.

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None

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Gametophyte

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Haploid cell that makes gametes by mitosis. Fertilization results in a diploid zygote that gives rise to the next sporophyte generation.

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Meiosis 1

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During interphase diploid cell replicates both homologous chromosomes. Now has 2 made from sister chromatids. Meiosis happens and the homologous chromosomes are separated.

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Meiosis 2

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The 2 haploid cells with replicated chromosomes split into 4 with unreplicated chromosomes.

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Meiosis Prophase 1

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Lasts longer and is more complex than prophase in mitosis. The chromosomes begin to condense and homologues each made of 2 sister chromatids pair up. Synapsis happens, and a protein structure called the synaptonemal complex attaches the homologous chromosomes tightly together all along their length. When the synaptonemal complex disappears in late prophase each chromosome pair becomes visible as a tetrad. Centrosomes move away from eath other and the spindle microtubules form between them. Nuclear envelope and nucleoli disappear. Mititic spindles catch kinetochores and the vhromosomes begin moving to the metaphase plate. It is the longest stage of meiosis and is usually more than 90% of the time of the process.

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Chiasmata

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The chromatids of homologous chromosomes are crisscrossed and hold the chromosomes together until anaphase 1. The physical manifestations of genetic rearrangement called crossign over.

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Metaphase 1

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Chromosomes arranged on metaphase plate still in homologous pairs. Kinetochore microtubules from one pole of the cell attached to one chromosome of each pair. Opposite pole attached to the homologue.

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Anaphase 1

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Spindle apparatus guides movement toward the poles, but they remain intact as sister chromatids.

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Telophase 1 and cytokinesis

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Members of each pair of homologous chromosomes continue to move apart until they reach the poles of the cell. Cleavage furrow or cell plate appears. Some species chromosomes decondense and the nuclear membrane and nucleoli reform. There is never further replication of genetic information before meiosis 2.

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Prophase 2

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Spindle apparatus forms and guides chromosomes to metaphase 2 plate.

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Metaphase 2

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Chromosomes positioned on the metaphase plate like in mitosis.

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Anaphase 2

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Centromeres of sister chromatids seperate, now individual chromosomes move to opposite poles.

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Telophase 2 and cytokinesis

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Nuclei form at opposite poles of cell. Now total of 4 haploid cells with unreplicated chromosomes.

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Synapsis

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Duplicate chromosomes pair with homologues in prophase 1.

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Synaptonemal complex

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Holds homologous chromosomes tightly together along their lengths