BIOL1003 Lecture Notes - Lecture 13: Microtubule, Chromone, Meiosis
19 May 2018
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Hormones
Sunday, 4 June 2017
2:49 PM
13. Reproductive system Page 1
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Screen clipping taken: 4/06/2017 11:20 AM
Meiosis terms
Sunday, 4 June 2017
11:20 AM
13. Reproductive system Page 2
Outline and explain meiosis
Occurs as part of the cell cycle
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In tissues that produce GAMETES (sex cells)
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Gametes must be haploid (single set of chromosomes n)
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When male and female gametes fuse during fertilisation,
resulting zygote then has correct number of chromones
(diploid - one haploid set from each parent)
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Chromosome sets reduced from diploid to haploid to form
gametes
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Each daughter cell is haploid, only has half as many
chromosomes as parent cell
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Screen clipping taken: 4/06/2017 12:06 AM
Chromosome number from 46 to 23
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Reduction division
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Similar to mitosis
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MEIOSIS I
Prophase I
Following interphase
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Genetic material replicated so 2 chromatids held together by centromere
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Initially chromosomes not visible but become more visible as they shorten and thicken
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Homologous chromosomes pair up
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Pair of chromosomes synapse, crossing over may occur
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Spindle fibres start to form
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Nuclear membrane breaks down and disappears
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Metaphase I
-chromosomes line up at equator of cell
One spindle fibre attaches to each centromere
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- random assortment of chromosomes occurs
Anaphase I
Homologous pairs separate
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Spindle fibres contract
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Move to opposite sides of cell
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Telophase I
New nuclei form and cell divides
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2 haploid daughter cells
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Cytokinesis I
Cytoplasm divides
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No pairing of homologues as they are located in separate cells
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MEIOSIS II
Prophase II
Spindle forms in new haploid daughter cells
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Metaphase II
Chromosomes line up along equator of spindle
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Each centromere attaches to spindle fibres from BOTH POLES
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Anaphase II
Centromeres divide
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Single chromatids move to opposite poles
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Chromatids now called CHROMOSOMES
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Constitute a complete set of chromosomes for the new nucleus
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Telophase II and
cytokinesis
Spindle disappears
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Nuclear membranes form
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Cytoplasm divides
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Chromosomes uncoil, elongate and fade from view
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DNA stretches out in nucleus to allow gene expression during
interphase
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Now left with 4 haploid nuclei from one diploid nucleus
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4 haploid cells = gametes (sperm/eggs)
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Daughter cells all genetically different and not identical to parent
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13a)
Saturday, 3 June 2017
11:58 PM
13. Reproductive system Page 3
Document Summary
Screen clipping taken: 4/06/2017 2:50 pm: reproductive system page 1. Screen clipping taken: 4/06/2017 11:20 am: reproductive system page 2. Genetic material replicated so 2 chromatids held together by centromere. Initially chromosomes not visible but become more visible as they shorten and thicken. Pair of chromosomes synapse, crossing over may occur. No pairing of homologues as they are located in separate cells. Each centromere attaches to spindle fibres from both poles. Constitute a complete set of chromosomes for the new nucleus. Dna stretches out in nucleus to allow gene expression during interphase. Now left with 4 haploid nuclei from one diploid nucleus. Daughter cells all genetically different and not identical to parent. Gametes must be haploid (single set of chromosomes n) When male and female gametes fuse during fertilisation, resulting zygote then has correct number of chromones (diploid - one haploid set from each parent) Chromosome sets reduced from diploid to haploid to form gametes.
