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1 COMPREHENSION QUESTIONS Multiple Choice Use the following informtion for questions 1 3. iploi somtic cell from rt hs totl of 42 chromosomes (2n = 42). s in humns, sex chromosomes etermine sex: XX in femles n XY in mles. 1. Wht is the totl numer of telomeres in rt cell in G2? c *e Wht is the totl numer of chromosomes present in the cell uring metphse I of meiosis?. 21 *. 42 c e Wht is the totl numer of chromosomes in polr oy cell from rt? * c e iviing eukryotic cell is trete with rug tht inhiits the moleculr motors ssocite with kinetochores. t which cell cycle stge woul it stop?. G1. S c. G2 *. M (nphse) e. M (telophse) 5. The figure shows chromosoml seprtion tking plce. The letters stn for genes; cpitl n lowercse stn for ifferent lleles. The iploi chromosome numer in this orgnism is four. Wht process is shown?. nphse of mitosis

2 . telophse of meiosis I c. nphse of meiosis I. telophse of mitosis *e. nphse of meiosis II C C True/Flse 6. Errors in chromosome seprtion re rrely prolem for n orgnism. (F) 7. The prokryotes inclue oth the eucteri n the rche. (T) 8. rche re more closely relte to eukryotes thn they re to eucteri. (T) 9. Generlly, chromosomes of eukryotes re circulr. (F) 10. Cells with single set of chromosomes re clle iploi. (F) Fill in the lnk 11. In flowering plnt, the mle prt of the flower (the stmen) prouces hploi microspores tht ivie y mitosis to prouce sperm. pollen grin tht lns on stigm grows pollen tue to eliver 2 (how mny?) sperm to the ovry. Fusion of sperm with n egg prouces 2 n cell clle zygote. To provie

3 foo for the eveloping emryo, tissue clle enosperm is prouce through oule fertiliztion. Enosperm hs ploiy of 3 n. 12. In prokryotes, repliction usully egins t specific plce on the chromosome clle the origin of repliction. 13. The nucler mtrix is the highly orgnize internl scffoling of the nucleus. 14. The ttchment point on the chromosome for spinle microtuules is the centromere. 15. Cytokinesis refers to the splitting of the cytoplsm, seprting one cell into two. Multiple Choice 16. Prokryotic chromosomes o not hve telomeres ecuse:. they o not go through mitosis.. they o not go through N repliction. c. they re in the cytoplsm. *. they re circulr. e. they hve no centromeres. 17. In eukryotes, chromosomes o not contin: *. riosomes.. chromtin. c. proteins.. histones. e. N. 18. In orer to e functionl, eukryotic chromosome requires ll of the following except:. centromere.. origins of repliction. *c. nucleoi.. telomeres. 19. Wht process is unique to plnts?. meiosis *. oule fertiliztion c. crossing over. hploi gmetes e. spermtogenesis 20. Suppose tht iploi cell contins 8 chromosomes (2n = 8). How mny ifferent comintions in the gmetes re possile?

4 . 2.4 c. 8 *. 16 e. 64 Use the following choices for questions Meiosis I prophse. Meiosis I nphse c. Meiosis II prophse. Meiosis II nphse e. Mitosis prophse f. Mitosis nphse 21. Chromosomes re in unseprte, sister-chromti form, t the en of the phse(s),, c, e. 22. The first stge fter which iviing cell tht strte s iploi woul e hploi. 23. Sister chromtis seprte uring, f. 24. Chromosomes re rnomly prtitione uring, contriuting to genetic iversity. 25. Crossing over (genetic recomintion) occurs in. Use the following informtion for questions Pe plnts hve seven ifferent types of chromosomes. 26. True or Flse? iploi pe cell in G1 hs 14 centrioles. (F) 27. The nucleus of megspore in pe ovry woul contin how mny chromosomes? nucleus in the pe enosperm contins how mny chromosomes? chromosome with centromere t the very en is clle:. sumetcentric.. metcentric. c. crocentric.. centric. *e. telocentric.

5 Short nswer 30. uring prophse I of meiosis, crossing over is inicte y wht microscopiclly visile structure? Chismt (chism) or the synptoneml complex 31. List two ifferences n two similrities etween mitosis n meiosis. ifferences:. Mitosis occurs in somtic (nonsex) cells; meiosis occurs in sex cells to prouce gmetes.. Meiosis involves chromosome piring (of homologous chromosomes); mitosis oes not. c. Mitosis prouces nonsex cells; meiosis prouces gmetes.. Mitosis prouces cells of the sme ploiy; meiosis prouces hploi cells from iploi cells. e. Meiosis hs two consecutive ivisions; mitosis hs one. f. Mitosis prouces two ughter cells; meiosis prouces four ughter cells. g. Mitosis prouces ienticl ughter cells; meiosis prouces four ifferent ughter cells. Similrities:. oth involve the seprtion of replicte chromosomes uring cell ivision.. oth re processes to ensure tht ughter cells in cell ivision receive complete set of chromosomes. c. N repliction must occur first.. Cytokinesis usully occurs t the en of ech.

6 32. The cells illustrte elow elong to species with iploi chromosome numer of four. Ech of the cells elow is in which stge of mitosis or meiosis?. meiosis I metphse. mitosis metphse c. mitosis nphse. meiosis I nphse e. meiosis II metphse For questions escrie the ifference etween: 33. centromere n kinetochore centromere is the physicl loction on chromosome where the kinetochore n spinle microtuules ttch. The kinetochore is compose of proteins tht ssemle on the centromere to provie site for the spinle microtuules to ttch. 34. G1 n G2 of the cell cycle

7 G1 occurs efore S phse n G2 occurs fter S phse. uring G1, cells grow in size, chromosomes re compose of single chromti. uring G1, cells pss criticl checkpoint (the G1/S checkpoint) fter which they re committe to unergoing cell ivision. uring G2, the chromosomes re compose of two chromtis. There is nother checkpoint uring G2 tht ensures cells re prepre for mitosis. Cells typiclly spen more time in G1 thn in G homologous chromosomes n sister chromtis Homologous chromosomes cn hve ifferent lleles. Sister chromtis re uplictes n (except for errors in repliction) re ienticl in sequence. 36. meiosis I n meiosis II Homologs pir n segregte in meiosis I. Sister chromtis re pire n segregte in meiosis II. Crossing over occurs in meiosis I, ut not in meiosis II. 37. sporophyte n gmetophyte The sporophyte is the iploi phse of plnt life cycle. The gmetophyte is the hploi stge. 38. Wht evience is there tht viruses evolve fter, not efore, cells? Viruses cn reprouce only within host cells. Thus, they must hve evolve fter cells. 39. Wht is one feture of meiosis tht prouces genetic vriility in gmetes? In two or three sentences, explin how this feture cuses genetic uniqueness. Inepenent ssortment. In meiosis I metphse n nphse nonhomologous chromosomes istriute rnomly. lignment n seprtion of one pir of homologous chromosomes is inepenent of how ifferent pir seprtes. ifferent gmetes hve ifferent comintions of the pternlly erive n mternlly erive chromosomes. These chromosomes cn hve ifferent lleles for the sme genes, so the gmetes normlly hve ifferent comintions of lleles. OR Crossing over. In meiosis I prophse portions of homologous chromosomes exchnge, chnging comintions of lleles of genes on single chromosome, so not

8 even sister chromtis re ienticl fter crossing over. Ech gmete hs only one copy of ech homolog, n ech homolog now hs unique comintion of lleles rw pir of telocentric homologous chromosomes s they woul pper in G2. Inicte centromeres with smll circle, n plce the lleles n on ech of the chromtis.. rw the sme chromosomes s they woul pper in G1. Plce the lleles n on ech of the chromtis. 41. Why is mitosis importnt within the cell cycle? single cell n ll its genetic informtion is uplicte. Ech cell contins full complement of chromosomes. 42. Explin why mitosis oes not prouce genetic vrition n how meiosis les to the prouction of tremenous genetic vrition. Mitosis prouces cells tht re geneticlly ienticl to the prent cell. Meiosis inclues two istinct processes tht contriute to the genertion of genetic vrition: crossing over shuffles lleles on the sme chromosome into new comintions, wheres the rnom istriution of mternl n pternl chromosomes shuffles lleles on ifferent chromosomes into new comintions. 43. Microscopy to look t cell's chromosomes is often one when the cell is in mitotic metphse. For exmple, kryotypes tht extrct chromosomes from

9 single cell n photogrph them to look for normlities re one on metphse, rther thn interphse, cells. Why? In metphse, chromosomes re conense n re more esily visulize. 44. Fin n escrie t lest four errors in the rwing elow of mitotic nphse. (1) Chromosomes tht re seprting re still uplicte. (2) Spinles re not coming from common spinle-pole oy. (3) Sister chromtis o not hve ienticl lleles for the gene. (4) Two lleles of the gene re on one chromosome. (5) No lleles of the gene re on the homologous chromosome. (6) Homologous chromosomes pper to hve pire n to e segregting

10 45. Wht events uring sexul reprouction re significnt in contriuting to genetic iversity? (1) Crossing over chnges llele comintions on chromosomes, so, fter meiosis I, even sister chromtis re not geneticlly ienticl. (2) Inepenent ssortment of non-homologous chromosomes ensures ech gmete hs ifferent comintion of lleles for genes on nonhomologs. (3) Two geneticlly unique gmetes from ech prent comine uring fertiliztion to form novel, geneticlly unique iniviul. 46. In tissue from the intestinl epithelium of frog, the following proportions of cells were foun t ech stge of the cell cycle: Stge Proportion of Cells Interphse 0.90 Prophse 0.04 Prometphse 0.02 Metphse 0.01 nphse 0.02 Telophse 0.01 If the entire cell cycle in frog epithelium cells requires 20 hours for completion, wht is the verge urtion of ech stge? = 18 hours, = 0.8 hours, =.4 hours, etc.

11 Use the following informtion for questions iploi, eukryotic cell in interphse hs these two pirs of homologous chromosomes with the inicte rrngement of lleles: 47. rw the chromosomes t the en of ) prophse of mitosis n ) prophse I (of meiosis I) with the most likely crossing over events. Inicte plcement of lleles on the chromosomes. )

12 ) 48. rw the chromosomes t the en of telophse of ) mitosis n ) meiosis II. Inicte plcement of lleles on the chromosomes. )

13 ) [One possiility] 49. Write ll possile genotypes of ech of the cells resulting from ) mitosis n ) meiosis, rwn in the previous question. Mitosis: / / / or / (iploi n heterozygous t ll three loci) Meiosis:,,, (hploi t ll three loci) 50.. Compre n contrst spermtogenesis n oogenesis in nimls. For ech process, e sure to inclue informtion out ivision of the nucleus, lloction of chromosomes to the vrious proucts, n ivision of the cytoplsm. ivision of the nucleus n lloction of the chromosomes to the proucts re essentilly the sme in oth processes. Strting with 2n germ cell, nucler ivision is y meiosis I n II, n ech prouct of meiosis contins one set of chromosomes (1n). The mjor ifference is tht ivision of the cytoplsm uring meiosis I n II is equl in spermtogenesis n unequl in oogenesis. uring oogenesis, meiosis I prouces lrge seconry oocyte with lots of cytoplsm n polr oy with very little cytoplsm. Meiosis II in the seconry oocyte prouces lrge ovum with lots of cytoplsm n smll secon polr oy.

14 Therefore, only one lrge, functionl egg is prouce per primry oocyte, wheres four smll, functionl sperm re normlly prouce per primry spermtocyte.. Why is the ifference in cytoplsmic ivision etween spermtogenesis n oogenesis importnt to reprouction, consiering the ifferent roles of sperm n eggs in reprouction? The smll size n other fetures of sperm structure suit them well to elivery of the hploi nucleus to the egg. The lrge mount of cytoplsm in the egg suits it well to nourishing evelopment of the emryo fter fertiliztion escrie the chnging role of cohesin uring the mitotic cell cycle. Cohesin keeps sister chromtis together fter N repliction uring S phse through metphse of mitosis. The rekown of cohesin llows the sister chromtis to seprte from ech other uring nphse.. Explin the importnce of regultion of cohesin ctivity to norml cell ivision. Cohesin must e ctive eginning in S phse through metphse in orer to keep the sister chromtis together so tht they cn e properly ligne t the metphse plte to ensure equl ivision of the genetic informtion to the two ughter cells. Cohesin must e inctivte or roken own in orer to llow the sister chromtis to seprte uring nphse so tht ech ughter cell will get one copy of the genes on ech chromosome. 52. List n riefly escrie the three mjor cell cycle checkpoints. For ech checkpoint, preict the consequences if the checkpoint file to work properly. (1) The G1/S checkpoint hols the cell in G1 until the cell hs ll of the enzymes necessry for repliction of N. If the checkpoint file, the cell woul procee into S without the necessry enzymes, cusing the N not to e replicte properly or completely. This might cuse the cell cycle to hlt t the G2/M checkpoint. lterntively, the cell might ivie without the genetic mteril hving een replicte, cusing the ughter cells to receive incomplete genetic informtion. (oth preictions re resonle se on informtion in the chpter.) (2) The G2/M checkpoint is psse only if the cell s N is unmge. If it fils to work properly, ivision woul procee in the presence of mge N, possily leing to muttions in the ughter cells n/or eth of the ughter cells.

15 (3) The spinle-ssemly checkpoint is uring metphse, n it ensures tht ech chromosome is ligne t the metphse plte n ttche to spinle fiers from opposite poles. This checkpoint epens on tension t the kinetochores of ech chromosome. If the checkpoint fils, nphse will occur even when the chromosomes re not ligne properly, llowing ughter cells to e prouce with extr n/or missing chromosomes.