* 13 Flashcards
1
Q
locus
A
a gene’s specific location along the length of a chromosome.
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
3
Q
gametes
A
develop from specialized cells called germ cells in the gonads.
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.
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.
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.
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))
