10.1 meiosis - mrs. shior's biology page! - home€¦ · 10.1 meiosis traits- characteristics...
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10.1Meiosis
Traits- characteristics you are born with !
ex: hair color, eye color, attached earlobes!!
The instructions are coded in DNA, located in your chromosomes!!
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Each chromosome contains hundreds of genes !
(humans have about 30,000 genes)
Genes- segments of DNA that control the production of a protein.!!
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Human cells have 46 chromosomes, !or 23 pairs (one from each parent).!!homologous chromosomes- !pairs of chromosomes !
-same length!-same centromere position!-carry genes for the same traits!
Karyotype
Chromosomenumbers:• Ciliatedprotozoa-15,000• Butterfly-268• Fern-184• Hedgehog-90• Sheep-54• Human-46• Tiger-38• Cabbage-18• Koala-16• FruitFly-8
gametes – sex cells with half the number of chromosomes !
Ex: egg and sperm!!To maintain the same number of chromosomes from generation to generation, organisms produce gametes.!
Haploid- a cell with n chromosomes !Diploid- a cell with 2n chromosomes!
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n = number of chromosomes in a gamete !!
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Skincell- haircell- spermcell-
Meiosis - cell division that reduces the number of chromosomes - produces gametes !
Requires two cell divisions, !meiosis I and meiosis II!!
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Meiosis!Copyright © McGraw-Hill Education
Meiosis I
Interphase-DNA replicates.!-Chromatin condenses.!
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Prophase I-Pairing of homologous chromosomes (one from mom, one from dad)!-Each chromosome consists of two sister chromatids (exact copies)!!
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Synapsis- a process during prophase/condensation which allows for crossing over. !Crossing over – DNA is exchanged between homologous chromosomes.!
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Homologouschromosomes-sisterchromatids
Metaphase Icentromeres attach to spindle fibers!Homologous chromosomes line up as a pair in the middle (equator)!
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Anaphase IHomologous chromosomes move apart.!chromosome number reduced from 2n to n!
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Meiosis!Copyright © McGraw-Hill Education
Telophase IChromosomes reach opposite poles.!
!Cytokinesis.!
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Meiosis II - second set of phases !!!**no second interphase**
Prophase IIspindle apparatus forms and chromosomes condense!
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Metaphase IIChromosomes line up in the middle (equator)!haploid number of chromosomes!
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Anaphase IISister chromatids pulled apart and move toward poles!
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Telophase IIchromosomes reach the poles!nuclear membranes reform!!! !
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Cytokinesis results in four haploid cells (n chromosomes)!!
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Each nucleus has !slightly different DNA!
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Mitosis !one cell division !two diploid (2n) cells!identical!
Meiosis !two cell divisions !four haploid (n) daughter cells !not genetically identical.!
• Meiosis = genetic variation.!
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The Importance of Meiosis- variation• During prophase I, chromosomes
line up randomly.!• Gametes end up with different
combinations of chromosomes.!• Genetic variation also comes from
crossing over and randomness of fertilization!
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Asexual reproduction (ex: mitosis)!• organism inherits all chromosomes from one parent!• offspring is genetically identical to its parent.!
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Sexual reproduction (ex: meiosis)!Rate of beneficial mutations is faster. !Beneficial genes multiply faster than for asexual organisms. !!
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