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15 Cards in this Set
- Front
- Back
What are introns
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Section of non coding DNA
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During which part of cell cycle is mutations likely to occur
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DNA synthesis
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What is an allele
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Different variation of a gene
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Describe appearance of chromosome
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Two chromatids joined by centrosome
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Name and explain parts of cell cycle
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Interphase: normal cell activity
First growth- proteins are synthesised DNA synthesise - DNA is replicated Second growth- organelles grow and divide |
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Explain crossing over
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Homologous Chromatids cross over
Chromatids break off and then attach to homologous chromosome This exchanges alleles |
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Name stages of cell division
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Prophase
Metaphase Anaphase Telophase |
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Describe what happens at each stage
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Prophase- nuclear envelope disintegrates and chromosomes become visible and dense
Metaphase- chromosomes line up down centre and spindle fibres form Anaphase- spindle fibres attach to centrosome and pull chromatids to polls of cell Telephase- chromatids become indistinct and nuclear envelope reforms |
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What is importance of reducing chromosome number in meiosis
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When fertilisation occurs the two gametes combine to to form original number
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Name 3 differences between meiosis and mitosis
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Mitosis-
1. Genetically identical 2. 1 cell division 3. No crossing over Meiosis 1. Genetically different 2. 2 cell divisions 3. Crossing over |
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Give two processes other than crossing over, which result In genetic variation
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Mutations
Independent segregation |
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Name number of chromosomes in diploid cell in humans
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46
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Name number in hapoid
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23
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Describe meiosis 1
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Homologous chromosomes line up and cross over.
Separate and divide |
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Describe meiosis 2
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Normal mitosis
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