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# Mitosis/ Chromosomes in Human Cells

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HeLa cells (a strain of human cells cultured in the laboratory) have a mitotic cycle of about 24 hours, of which about 11 hrs is spent in G1, about 8 hrs in S, about 4 hrs in G2, and about 1 hr in mitosis. If you took a sample of HeLa cells from a culture, and looked at it through the microscope, in about what % of cells would you expect the chromosomes to be visible?

The answer is about 1 cell in 24, or 4.2%, would be expected to have visible chromosomes.

I have been doing this problem several times now and I can't figure out how to do it. I am so confused. Can you also explain the number of chromosomes you get from mitosis?

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https://brainmass.com/biology/the-cell-division-cylce/mitosis-chromosomes-human-cells-82105

#### Solution Preview

Hi,

The first part of your question is one sometimes examined in cell biology labs where mitosis (cell division) is being observed ( for an example and some explanations of key concepts see http://dbs.umt.edu/courses/biol101S04/labs/Wyrick_s04/11_cell_cycle.htm). An assumption made during these exercises is that, given a statistically sufficient sample of the total cell population, the number of cells you see in a given phase is equal to the time they spend in that phase. Since the total time required for cell division to take place in the HeLa cells is 24 hrs, and the length of time cells spend in mitosis is one ...

#### Solution Summary

This solution provides assistance determining at what percentage of cells one could expect the chromosomes to be visible from a sample of HeLa cells form a culture, and explains the number of chromosomes you get from mitosis.

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## Mitosis & Meiosis

Please identify these questions as true or false.

1. Crossing-over is relatively infrequently between any two genes, but always occurs somewhere during meiosis.

2. Sister Chromatids have identical alleles.

3. Cells that divide by meiosis become haploid after the first division (meiosis I).

4. In humans, the only cells that can divide by meiosis would be found in the testes and ovaries.

5. Homologous pairs are produced when DNA replicates during S phase prior to mitosis or meiosis.

6. For a human cell, N=23, meaning that cells that have completed meiosis I have 23 chromosomes.

7. Anaphase of mitosis and anaphase of meiosis II are similar in that sister chromatids separate from each other.

8. After meiosis I, the two daughter cells are temporarily diploid.

9. A normal human cell has 46 chromosomes at every stage of meiosis.

10. Homologous chromosomes are paired only during prophase of meiosis.

11. Homologous chromosomes have the same genes.

12. A cell never divides, such as a nerve cell, is in the G1 phase of the cell cycle but can't pass through the checkpoint into G2.

13. At the end of meiosis I, the two daughter cells produced by a dividing germ cell are haploid and genetically different.

14. A mutation would be inherited only if it occurs in the DNA of a germ cell.

15. At any given time, every cell in the human body would be in one of the four phases of the cell Cycle: G1, S, G2 or M.

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