Term
o unreplicated and replicated chromosomes are each considered single chromosomes, even though the replicated chromosome comprises two sister chromatids
• A chromosome is still just one chromosome whether it consists of one strand or two identical strands. |
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Definition
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Term
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Definition
o based on role of chance; requires a small sample size
• modern travel and migration decreases the chance of there being a small, isolated population and therefore genetic drift |
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Term
| bivalent (book uses tetrad) |
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Definition
group of four chromatids produced when homologs synapse
• consists of two homologous chromosomes, with each homolog consisting of two sister chromatids |
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Term
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Definition
o homologs in each chromosome pair separate from each other
• one homolog goes to each daughter cell
o diploid (2n) parent cells produce two haploid (n) daughter cells
• each chromosome still consists of two sister chromatids |
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Term
| early prophase I of meiosis |
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Definition
• chromosomes condense, spindle apparatus forms, and nuclear envelope begins to disappear
• homologous chromosomes pairs come together (synapsis) - possible because similar regions of homologous chromosomes attract each other
• spindle fibers attach to kinetochores at centromeres of chromosomes |
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Term
| late prophase I of meiosis I |
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Definition
• crossing over results in mixing of chromosome segments from maternal and paternal chromosomes
• non sister chromatids begin to separate, but stay joined in certain locations and cross over each other
o normally at least one chiasma in every pair of homologous chromosomes
o chromatids involved are homologous but not sisters
o physical exchange of paternal and maternal chromosomes |
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Term
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Definition
| X-shaped structure formed from crossover |
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Term
| metaphase I from meiosis I |
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Definition
• pairs of homologous chromosomes (bivalents/tetrads) moved to metaphase plate by spindle fibers and line up
• each tetrad moves independent of other tetrads
• alignment of maternal and paternal homologs from each chromosome is random |
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Term
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Definition
| homologous chromosomes in each tetrad separate and move to opposite poles |
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Term
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Definition
| homologs finish moving to opposite poles, in some species a nuclear envelope re-forms around each set of chromosomes |
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Term
| cytokinesis at end of meiosis I |
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Definition
| marks end of meiosis I, forming two haploid daughter cells |
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Term
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Definition
o one chromosome of each homologous pair distributed to a different daughter cell
• reduction division
• sister chromatids remain attached, which means haploid daughter cells still contain replicated chromosomes
• produces two haploid cells |
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Term
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Definition
o similar to mitosis in haploid cell
• in both, chromosome movements caused by spindle fibers pulling chromatids apart
o sister chromatids from each chromosome separate, one to each daughter cell
o cells produced by meiosis II also have one of each type of chromosome, but now the chromosomes are unreplicated
o end result: four haploid cells |
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Term
| DNA content is halved in ________ |
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Definition
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Term
| ploidy level changes from diploid to haploid in _________ |
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Definition
| meiosis I, and remains haploid in meiosis II |
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Term
| crossing over occurs between _______ |
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Definition
| nonsister chromatids of homologous chromosomes |
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Term
| variation among offspring & fact that they are genetically different from their parents is due to ________ |
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Definition
| crossing over, random process of fertilization, and random alignment of homologues during meiosis I |
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Term
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Definition
| adaptation to a changing environment occurs most efficiently through sexual reproduction |
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Term
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Definition
| number and types of chromosomes present |
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