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24

In which phase of meiosis are the following formed? Choose the answers from hint points given below.

(a) Synaptonemal complex ........... .

(b) Recombination nodules ........... .

(c) Appearance/activation of enzyme recombinase ............ .

(d) Termination of chiasmata ......... .

(e) Interkinesis ............ .

(f) Formation of dyad of cells .......... .

Hints (a) Zygotene,

(b) Pachytene,

(c) Pachytene,

(d) Diakinesis,

(e) After Telophase-I/before prophase of meosis-II,

(f) Telophase-I/after meiosis-I.

Explanation

(a) Synaptonemal complex zygotene.

(b) Recombination nodules pachytene.

(c) Appearance/activation of enzyme recombinase telophase-l/after, meiosis-l ... .

(d) Termination of chiasmata diakinesis.

(e) Interkinesis after telophase-I/before prophase of meiosis-II.

(f) Formation of dyad of cells pachytene.

25
State the role of centrioles other than spindle formation.
Explanation
The two centrioles in the centrosome lie perpendicular to each other. Each has organisation like a cart wheel. These form the basal body of cilia and flagella of plant/animal cells besides forming spindle fibre in animal cell division. It also helps in the formation of microtubuless and sperm tail.
26
Mitochondria and plastids have their own DNA (genetic material). What is known about their fate during nuclear division like mitosis?
Explanation
The DNA present in mitochondria and chloroplast is extrachromosomal DNA. It has nothing to do with the nuclear divisions. In mitosis, only nuclear DNA takes part.
27

Label the diagram and also determine the stage at which this structure is visible.

Explanation

The diagram shows the transition stage between prophase and metaphase stage of mitotic cell division.

28
A cell has 32 chromosomes. It undergoes mitotic division. What will be the chromosome number ( $n$ ) during metaphase? What would be the DNA content (C) during anaphase?
Explanation
The mitotic cell division occurs in somatic cells of an organism. The chromosome number in the daughter cells remain same as that of the parent (dividing) cell, so even at metaphase or anaphase, the chromosome number does not change. The DNA content gets doubled at the synthetic phase of interphase and gets divided at anaphase but the chromosome number remains same.
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