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1 Antibiotics are chemicals that interfere with the cell cycle of bacteria. Methicillin-resistant Staphylococcus aureus (MRSA) strains were inoculated or grown in LB agar medium, and the listed antibiotics were spotted identically on the surface of each of the Vector plate. Dark halos at the position of each antibiotic spot show the zone of growth inhibition produced by each antibiotic. The larger the dark, circular halo is the greater the effect the antibiotic had on the bacterial cell cycle or cell division.

A

How does 1 bacterium, or a few bacteria, as grown in the agar plate shown above increase to be a colony of billions of cells?

BWhy are bacteria, such as MRSA, able to become resistant to the effects of an antibiotic that is frequently used?

Restoring Methicillin-Resistant Staphylococcus aureus Susceptibility to β-Lactam Antibiotics Christopher M. Tan et. al. Sci Transl Med 21 March 2012 4:126ra35

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2

A

Provide a hypothesis for the following scenario: if you would express anthox1a in the early blastula stage (A), what might you expect?

B

Create a diagram showing the progression of the Hox genes through the developmental stages of the sea anemone.

CHow do the cell cycle and the expression of Hox genes help develop an organism such as the sea anemone?

Developmental expression of Hox genes in the sea anemone Nematostella vectensis. The apical or aboral pole is toward the left and opposite to the blastoporal pole (*, asterisks), the site of the future mouth. All images are seen from the lateral aspect (side view), except for (B), which is an aboral view. Expression of anthox1 in (A) early blastula stage and (B and C) planula larva stage. Expression of anthox1a in (D and E) gastrula and (F) late larval stages. Expression of anthox7 in (G and H) gastrula and (I) late larval stages. Expression of anthox8 in (J and K) gastrula and (L) late larval stages. Expression of anthox6 in (M) early larval stage and (N) juvenile polyp. bc, blastocoel; ec, ectoderm; ecph, pharyngeal (ph) ectoderm; en, endoderm; enph, pharyngeal (ph) endoderm; enbw, body wall (bw)endoderm; mes, mesentery; and tn, tentacles.

Origins of Bilateral Symmetry: Hox and Dpp Expression in a Sea Anemone

John R. Finnerty, Kevin Pang, Pat Burton, Dave Paulson, and Mark Q. MartindaleScience 28 May 2004: 304 (5675), 1335-1337.

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3

AHow are mitosis and interphase related in the cell division cycle?

B

Animal cells have centrioles, but some cells, like plant cells or bacteria, do not have centrioles, describe some reason why centrioles might be important to animal cells?

C

The diagrams above depict mitosis and related processes. Some of the related processes are involved during meiosis as well. Describe and draw how meiosis differs from mitosis.

Centrosome behavior during the cell division cycle.

(A) Cells in G1 contain a single centriole pair, composed of an old (green bar) and a new (red bar) centriole. Both centrioles are usually located close to the nucleus (blue) and are surrounded by components of the centrosome (yellow dots), which initiate microtubule assembly. The centrioles duplicate conservatively during interphase, producing two pairs each composed of a mother centriole and a daughter centriole (yellow bar). As cells prepare to enter mitosis, the two centrosomes (each containing a centriole pair) move apart to opposite sides of the nucleus, so that they can act as the poles of the mitotic spindle after the nucleus breaks down. In anaphase, the connection between the mother and daughter centrioles is broken. (B) Centrosomal components and microtubules can organize themselves into a centrosome-like structure in cells that lack centrioles. (C) Chromosomes (blue) can alter the local distribution of microtubules; and chromosomes, microtubules, and microtubule motors can interact to form a bipolar spindle. (D) Microtubules and microtubule motors (red dots) can self-organize in glass chambers the same size as cells.

Centrioles at the CheckpointAndrew W. MurrayScience 23 February 2001: 291 (5508), 1499-1502.

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4 To study the role of the CKS2 gene in the cell cycle, both alleles of the CKS2 gene were removed from wild-type, normal mice, generating CKS2–/– mice.

Some of the results of the experiment are shown in figures A and B. (A) Testis sections from adult wild-type mice were stained with hematoxylin and eosin (a dye that colors nuclei blue-like and proteins pink-like). Spermatocytes (sperm cell precursors) in different stages of the cell cycle can be seen (red arrowheads and green arrowheads. (B) Testis section from an adult CKS2–/– mouse showing cells up to one stage or phase in the cell cycle (red arrowheads). Original magnification, ×400.

ADescribe the effect that the CKS2 gene product has on the cell cycle.

BWhy will CKS2–/– mice not be able to pass their genetic information to subsequent generations?

C

How does the process shown in the cells in figure A affect the genetic diversity of the organism that contains those cells and the offsprings that are produced by those cells?

Requirement of Cks2 for the First Metaphase/Anaphase Transition of Mammalian MeiosisCharles H. Spruck, Maria P. de Miguel, Adrian P. L. Smith, Aimee Ryan, Paula Stein, Richard M. Schultz, A. Jeannine Lincoln, Peter J. Donovan, and Steven I. ReedScience 25 April 2003: 300 (5619), 647-650.

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5 Divergent silencing of duplicate genes in sister species. The ancestral species may acquire a duplication of an essential gene (represented by the black bars on two pairs of parental nonhomologous chromosomes). Either copy of the duplicate gene pair (white bars) may be randomly lost in the two descendant populations through geographic isolation (living apart) or divergent gene silencing (gene is turned off through mutations or chromosomal modifications). In this case, the first-generation (F1) hybrid progeny of these two populations will contain two “absentee” alleles, one at each chromosomal locus. As a consequence of independent assortment, 25% of the gametes produced by these individuals will be entirely lacking an active copy of the original ancestral, essential gene; therefore those gametes would not be functional and produce nonfunctional progeny or be sterile. The above process repeated over a period of time can produce new species from an ancestral population.

A

Once the duplicated gene is introduced into ancestral species, how is the gene maintained in each cell of the species?

B

After the two isolated species are allow to mate and produce offspring (hybridization), why does the hybrid contain one active and one silence allele of the essential, ancestral gene?

CDescribe or draw the allelic combinations that will be produced by meiosis in the hybrid offspring?

Gene Duplication and EvolutionMichael LynchScience 9 August 2002: 297 (5583), 945-947.