Compare and contrast chromatin and chromosomes (either structurally or functiona

Question

Compare and contrast chromatin and chromosomes (either structurally or functionally) Compare: Contrast: Compare and contrast diploid and haploid cells (either structurally or functionally) Compare: Contrast: When comparing diagrams of mitotic stages to actual cells through a microscope, why do you typically not find "textbook picture perfect" stages? Do you think you could construct a karyotype without using a stain (like Giemsa stain)? Explain why or why not. Why do you think we used onion root tip cells in the lab and in the simulation instead of, for example, onion leaf cells?

Explanation / Answer

Ans. 1.

Compare: Chromatin: DNA complexed with its cognate protein (histones, etc.) is called chromatin.

            Chromosome: It is the condensed (supercoiled) form of chromatin formed during M-phase of mitosis or meiosis.

Contrast: Though both are chemically the same, they differ in their transcriptional activity.

The genes on relatively less condensed chromatin can be transcribed during G0 and G1 phase. Due to supercoiling, the genes on chromosomes can’t be accessed by transcription machinery and can’t be transcribed.

Ans. 2.

Compare: Diploid cell has two complete set of genome- one set from mother, another set from father.

Haploid cell has a single set of chromosome.

Contrast: Diploid cells are result of mitosis in a diploid cell. Generally involved in normal metabolism and maintenance of the body in higher animals and plants.     

Haploid cells are produced when a diploid cell undergoes meiosis (gametogenesis). Generally form gametes and participate reproduction in higher animals and plants.   

Ans. 3. Many subcellular structures like microtubules (spindle fibers), nuclear membrane, etc., may not be visible under light microscope. Moreover, the chromosomes are also not well separated as shown in textbook figures. Therefore, under microscope, an independent chromosome can’t be seen beautifully arranged at the equator in metaphase or at their respective place in any other phase of mitosis.

Ans. 4. Chromosomes and other cellular components are usually colorless. So they can’t be visualized under light microscope most of the times because the background of the microscope is also colorless (bright light). Assume a glass slab over another glass slab lying flat on floor- visually they appear one (not differentiated) when viewed from top.

Staining provides some color to the cellular components, say chromosomes. Stained chromosomes appear different from background, say red colored chromosomes against white background. Thus, staining visually differentiates chromosomes from background and makes karyotype possible.

Karyotype is not possible without suitable staining because it does not visually differentiate colorless chromosomes from colorless background.

Ans. 5 Onion root tip is a meristem tissue and undergoes rapid cell divisions under appropriate conditions- when onion root is dipped in water. So, a tissue with continuously diving cells (higher mitotic index) in it gives many cells at different stages of cell cycle- a good sample to study cell cycle. Stages under light microscope.

Leaf cells are differentiated cells and generally don’t enter mitosis. So, it’s very difficult to find a cell in M phase from a leaf sample.            

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