1.) Neural crest cells that migrate along the dorso-lateral pathway between the

Question

1.) Neural crest cells that migrate along the dorso-lateral pathway between the ectoderm and somites give rise to __________________cells.

2.) What accounts for the variation in the size of eggs (why are some big and some small)? ___________________

3.) When chromatin is tightly wound and highly compacted it is called _____________________.

4.) Radial intercalation of presumptive ectodermal cells of the Xenopus blastula/gastrula results in ______________________

5.) What is the source of the reprogramming factors that allow for the cloning of an animal (e.g. Dolly) by somatic cell nuclear transfer? ___________________

6.) What organelle of the sperm enters the egg cytoplasm and participates in organization of the first mitotic spindle? _______________________

Explanation / Answer

1. Epidermal melanocytes which are pigment cells.

2. Restriction on female body conditions lead to variation in egg sizes.

3. Heterochromatin

4. Radial intercalation of presumptive ectodermal cells of xenopus blastula/gastrula results in enlargement of the outer surface by ectodermal cells.

5. Oocyte is the main source of reprogramming factors, so it is actually oocyte induced reprogramming that allow for the cloning of an animal by SCNT. in this technique, nuclei of oocyte is removed, and nuclei of somatic cell is then injected into oocyte, which provide reprogramming factor to the somatic nuclei.

6. Sperm nuclei enters the egg and it is drawn through the egg cytoplasm close to egg cytoplasm. when sperm nuclei fused with egg nuclei, then diploid number of chromosome is restored. A spindle is formed for first mitotic division. paternal and maternal chromosomes are arranged together on spindle and leads to first mitotic division of fertilised egg.

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