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प्रश्न
Describe the structure of sex chromosomes with the help of labelled diagram.
उत्तर
Structure of X and Y chromosomes:
- The x chromosome is straight, rod-like, and longer than the Y chromosome.
- The x chromosome is metacentric, while the Y chromosome is acrocentric.
- The x chromosome has a large amount of euchromatin (extended region) and a small amount of heterochromatin (highly condensed region).
- Euchromatin has a large amount of DNA material, hence the X chromosome is genetically more active.
- The y chromosome has a small amount of euchromatin and a large amount of heterochromatin, hence it is genetically less active or inert.
- Both X and Y chromosomes show homologous and non-homologous regions.
- Homologous regions show similar genes while non-homologous regions show dissimilar genes.
- Crossing over occurs only between homologous regions of X and Y chromosomes.
- The non-homologous region of the X chromosome is longer and contains more genes than that of a non-homologous region of the Y chromosome.
- X-linked genes are present on the non-homologous region of the X-chromosome while Y-linked genes are present on the non-homologous region of the Y-chromosome.
संबंधित प्रश्न
“First meiotic division is the reduction division” what does the word ‘reduction’ refer to in this statement?
Choose the correct answer:
If after karyokinesis, cytokinesis does not occur, then result would be _____________
Write a sentence of the following:
Centromere
(i) Draw a neat labeled diagram to show the metaphase stage of mitosis in an animal cell having ‘6’ chromosome.
(ii) How many daughter cells are formed at the end of mitosis and at the end of meiosis?
(iii) With reference to cell division explain the following terms:
(Chromatid, Centromere, Haploid).
(iv) Name the type of cell division that occurs during:
1. Growth of shoot 2. Formation of pollen grains.
3. Repair of worn out tissues.
Give Technical Terms
The stage at which the formation of chiasmata occurs.
Mention, if the following statement is True or False. If false rewrite the wrong statement in its correct form:
Chromosomes are the thickest and shortest in telophase.
Multiple Choice Question:
The disappearance of spindle and uncoiling of chromosomes takes place in
Name the following:
Cells having a single set of chromosomes.
Column ‘II’ is a list of items related to ideas in Column ‘I’. Match the term in Column ‘II’ with a suitable idea given in Column ‘I’.
| Column I | Column II |
| Genetics | Chromosomes are similar in size and shape. |
| Autosomes | The alternative forms of a gene. |
| Recessive gene | Study of laws of inheritance of characters |
| Allele | A gene that can express only when in a similar pair. |
| Homologous chromosomes | Chromosomes are other than the pair of sex chromosomes. |
Match the following.
| 1. Autosomes | - | Trisomy 21 |
| 2. Diploid condition | - | 9 : 3 : 3 : 1 |
| 3. Allosome | - | 22 pair of chromosome |
| 4. Down’s syndrome | - | 2n |
| 5. Dihybrid ratio | - | 23rd pair of chromosome |
