17–12 A living cell from the lung epithelium of a newt is shown at different stages in M phase in Figure Q17–2. Order these light micrographs into the correct sequence and identify the stage in M phase that each represents.
Figure Q17–2 Light micrographs of a single cell at different stages of  m phase (problem 17–12). (Courtesy of Conly L. Rieder.) 17–13 Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18) are the most common autosomal trisomies seen in human infants. Does this fact mean that these chromosomes are the most difficult to segregate properly during meiosis?
17–14 The human genome consists of 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes). During meiosis, the maternal and paternal sets of homologs pair, and then are separated into gametes, so that each contains 23 chromosomes. If you assume that the chromosomes in the paired homologs are randomly assorted to daughter cells, how many potential combinations of paternal and maternal homologs can be generated during meiosis? (For the purposes of this calculation, assume that no recombination occurs.)
Overview of the Cell Cycle morgan dO (2007) The Cell Cycle: principles of Control. London: new science press.
murray aW & Hunt T (1993) The Cell Cycle: an Introduction. new York: WH Freeman and Co.
The Cell-Cycle Control System
Evans T, Rosenthal ET, Youngblom J et al. (1983) Cyclin: a protein specified by maternal mRna in sea urchin eggs that is destroyed at each cleavage division. Cell 33, 389–396.
Hartwell LH, Culotti J, pringle JR et al (1974) genetic control of the cell division cycle in yeast. Science 183, 46–51.
Holt LJ, Tuch BB, Villen J et al. (2009) global analysis of Cdk1 substrate phosphorylation sites provides insights into evolution. Science 325, 1682–1686.
nurse p, Thuriaux p & nasmyth k (1976) genetic control of the cell division cycle in the fission yeast Schizosaccharomyces pombe. Mol. Gen. Genet. 146, 167–178.
pavletich np (1999) mechanisms of cyclin-dependent kinase regulation: structures of Cdks, their cyclin activators, and CIp and Ink4 inhibitors. J. Mol. Biol. 287, 821–828.
primorac I & musacchio a (2013) panta rhei: The apC/C at steady state. J. Cell Biol. 201, 177–189.
Wittenberg C & Reed sI (2005) Cell cycle-dependent transcription in yeast: promoters, transcription factors, and transcriptomes. Oncogene 24, 2746–2755.
arias EE & Walter JC (2007) strength in numbers: preventing rereplication via multiple mechanisms in eukaryotic cells. Genes Dev. 21, 497–518.
Bell sp & kaguni Jm (2013) Helicase loading at chromosomal origins of replication. Cold Spring Harb. Perspect. Biol. 5, a010124.
groth a, Rocha W, Verreault a et al. (2007) Chromatin challenges during dna replication and repair. Cell 128, 721–733.
masai H, matsumoto s, You Z et al. (2010) Eukaryotic chromosome dna replication: where, when, and how? Annu. Rev. Biochem. 79, 89–130.