Describe the differences between heterochromatin and euchromatin in chromosomes.

Question

Describe the differences between heterochromatin and euchromatin in chromosomes. Are three any situations in which one can be changed into the other? One of the strands in a DNA double helix has the nucleotide sequence 65: ACCTGCTACGG-3. What is the sequence of the complementary DNA strand? In an experiment with an Hfr cell if the uvrA gene is transferred 1 minute and the pyrB gene is transferred at 2.5 minutes then where is the oriT of the Hfr cell located? Use the map of E. coil genome presented below. Given the following sequence of genes on a chromosome, determine what change in chromosome structure occurred, (the * indicates the centromere) before A B C * E F G H after A B C D * E F E F G H Given the following sequence of genes on a chromosome, determine what change in chromosome structure occurred, (the * indicates the centromere) before A B C D * E F G H after A C D * E F G H

Explanation / Answer

Q. no. 16 -

Euchromatin:

1. The chromatin fibres in this region are loosely coiled as compared with hetero­ chromatic regions

2. Euchromatin is deeply stained in divisional cycle but less stained in interphase.

3. The region is genetically active and con­tains unique DNA.

4. Euchromatic regions are able to synthesize mRNA in vitro.

5. Euchromatic regions are seen to their DNA earlier than heterochromatin. They replicate during ‘S’ phase.

6. Due to addition or loss of this region phenotype is affected.

7. This region is not sticky.

Heterochromatin:

1. The chromatin fibres in this region are more tightly folded than euchromatic regions.

2. Heterochromatin is deeply stained in interphase but less stained in divisional cycle.

3. Heterochromatic regions are unable to synthe­size mRNA in vitro.

4. Heterochromatic regions are unable to synthe­size mRNA in vitro size mRNA in vitro.

5. Heterochromatic regions are seen to replicate during the onset of divisional cycle.

6. Addition or loss of this region does not affect phenotype.

7. This region is sticky.

Q. no. 17 -

3' TGGACGATGCC 5'

Q. NO. 19 -

before A B C D * E F G H
after A B C D * E F E F G H ~ gene duplication

Q. NO. 20 -

before A B C D * E F G H
after A C D * E F G H ~ interstitial deficiency

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