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22 Cards in this Set
- Front
- Back
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Meiosis produces...
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...4 genetically different daughter cells |
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Step 1 of meiosis |
DNA replicates so there are 2 copies of each chromosome, called chromatids |
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Step 2 |
DNA condenses to form double-armed chromosomes each made from 2 sister chromatids |
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Step 3 |
chromosomes arrange themselves in homologous pairs |
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what's a homologous pair? |
pair of chromosomes, 1 paternal and 1 maternal that have the same gene loci |
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step 4 of mitosis |
homologous pairs separated, halfing chromosomes number |
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step 5 (meiosis II)
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pairs of sister chromatids that make up each chromosome are separated |
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describe crossing over (recombination) |
When homogolous pairs of chromosomes come together and pair up They twist around each other Portions of chromatids break off and recombine with chromatids of its homogolous partner |
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what does crossing over result in? |
a different combination of alleles; genetic variation |
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what is substitution |
when one base is substituted for another |
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what is deletion |
when one base is deleted |
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what is directional selection? |
where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce |
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what is stabilising selection? |
where individuals with alleles for characteristics towards middle of range are more likely to survive and reproduce |
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when does stabilising selection occur? |
when the environment isn't changing |
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when does directional selection occur? |
when the environment is changing |
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state the chromosome formula |
(2n)^2 n = no. of pairs of homologous chromosomes |
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what's a gene |
a length of DNA that codes for a polypeptide |
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what's a locus |
position of a gene on a chromosome or DNA molecule |
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what's an allele |
one of the different forms of a particular gene |
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diploid.. |
..cells in which the nucleus contains two sets of chromosomes |
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haploid.. |
cells that contain only a single copy of each chromosome |
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define crossing over |
the process where a chromatid breaks during meiosis and rejoins to the chromatid of a homogolous chromosome so that their alleles are exchanged |
