Page 48 - Biology - XII

Comments
Diff erent stages are identifi ed and discussed separately.

Primary spermatocytes show these following stages:
Prophase I
1. Leptotene (Leptos—thin). This stage is identifi ed by—
(a) The nucleus enlarges in size and occupies most of the cell volume.
(b) The chromatin material forms long slender thread-like structures called chromosomes.
(c) Nuclear membrane is clear.

(d) Nucleolus is also seen.
2. Zygotene (Zygo—pair). This stage is identifi ed by—
(a) The chromosomes pair up. These pairs are called bivalents.
(b) The chromosomes become thick and short.
(c) Nuclear membrane is present.

(d) Nucleolus is also seen.
3. Pachytene (Pachy—thick). This stage is identifi ed by—
(a) The chromosomes become more thick.
(b) They split lengthwise to form sister chromatids. (This condition of chromosome is called tetrad.)
(c) The chromatids coil at places (This is called crossing over). The point of contact is called chias-
mata.
(d) Nuclear membrane and nucleolus is present.

4. Diplotene (Diplo—two). This stage is identifi ed by—
(a) The paired chromosomes start separating.
(b) Nuclear membrane starts to disappear.
(c) Nucleolus starts to disappear.
5. Diakinesis (Di—moving between). This stage is identifi ed by—
(a) The chromosomes become more thick.

(b) The chromosomes separate.
(c) Nuclear membrane disappears.
(d) Nucleous disappears.
Metaphase I. This stage is identifi ed by—
(a) The nuclear membrane disappears.

(b) The nucleolus also disappears.
(c) The centromere of the chromosome is attached to the spindle fi bres. The centromere faces the
centriole/pole of the cell.
(d) The chromosomes are arranged at the equator of the cell.
Anaphase I. This stage is identifi ed by—

(a) The bivalent chromosomes are pulled and pushed apart.
(b) They come and lie at opposite poles of the cell.

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