* 13 Flashcards

1
Q

locus

A

a gene’s specific location along the length of a chromosome.

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2
Q

homologous chromosomes

A

the two chromosomes composing a pair. two sister chromatids make up one duplicated chromosome. the two chromosomes of a homologous pair are individiual chromosomes that were inherited from diff parents.6

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3
Q

gametes

A

develop from specialized cells called germ cells in the gonads.

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4
Q

early prophase I

A
  • chromosomes condense, and homologs loosely pair along their lengths, aligned gene by gene.
  • paired homologs become physically connected to e/o along their lengths by a zipper-like protein structure, the SYNAPTONEMAL COMPLEX; this state is called SYNAPSIS.
  • crossing over: during synapsis; genetic rearrangement btwn non-sister chromatids involving the exchange of corresponding segments of DNA molecules.
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5
Q

chiasmata

A
  • The X-shaped, microscopically visible region where crossing over has occurred earlier in prophase I between homologous nonsister chromatids.
  • appears as a cross b/c sister chromatid cohesion still holds the 2 original sister chromatids together, even in regions beyond the crossover point, where one chromatid is now part of the other homolog.
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6
Q

events unique to meiosis

A
  • synapsis and crossing over
  • at metaphse I of meiosis, chromosomes are positioned at the metaphse plate as pairs of homologs (4 chromatids), rather than individual chromosomes (2 chromatids), as in metaphase of mitosis.
  • at anaphase I of meiosis, the duplicated chromosomes of each homologous pair move toward opposite poles, but the sister chromatids of each duplicated chromosome remain attached to e/o. in anaphase of mitosis, sister chromatids separate.
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7
Q

2 types of division

A
  • reductional: meiosis I. it halves the number of chromosome sets per cell – a reduction from 2 sets to 1 set (diploid to haploid state). (for 2n = 6, start w/ 12 chromatids per cell, end w/ 6 (3 X’s))
  • equational: meiosis II. sister chromatids separate. (start w/ 6 chromatids per cell, end w/ 3. (3 single segments))
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