BOTANY Higher Secondary Second Year - Textbooks Online

Chromosomal puff
Dark band
inter band
Polytene chromosome
Chromosome
axis
Lateral
Loop
Lamp brush chromosome
Fig. 3.3. Special types of chromosomes
113
chromosome is that along the
length of the chromosome there
is a series of dark bands
alternate with clear zones called
inter bands. The polytene
chromosome has extremely
large puff called Balbiani ring.
It is also known as
chromosomal puff. As this
chromosome occurs in the
salivary gland it is known as
salivary gland chromosomes.
Lamp brush chromosomes
were first observed by
Flemming in 1882. It looked like brushes. They occur at the diplotene
stage of meiotic prophase in oocytes of an animal Salamandor and in
giant nucleus of the unicellular alga Acetabularia. The highly condensed
chromosome forms the chromosomal axis, from which lateral loops of
DNA extend as a result of intense RNA synthesis.
Self evaluation
I . Choose and write the correct options.
1. The term chromosome was introduced by
a. Bridges b.Waldeyer c. Balbiani d. Flemming
2. Who had first proved that the genes are carried by the
chromosome?
a. Bridges b.Waldeyer c. Balbiani d. Flemming
II. Answer the following questions in two or three sentences.
3. What are autosomes?
4. What are sex chromosomes?
5. What are B–chromosomes?
6. What is a polytene chromosome?
III. Answer the following questions in about 100 words.
7. Write short notes on the structure of chromosomes.
8. Write short notes on the types of chromosomes.
9. Describe special types of chromosomes.