When early embryonic blastomere developmental fates are predetermined, cleavage is described as____________?
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Answer: D. Spiral and determinate
Explanation
When early embryonic blastomere developmental fates are predetermined, cleavage is described as spiral and determinate. Determinate cleavage restricts the developmental potential of each early blastomere very early on. Spiral cleavage involves oblique cell divisions that create a distinct alternating cellular packing arrangement. Determinate cleavage is characteristic of protostome embryos such as mollusks and annelids. If a blastomere is removed from a determinate embryo, the remaining cells cannot form a complete organism. Spiral cleavage patterns result from specific oblique angles of mitotic spindle positioning during early divisions.
Embryonic cleavage patterns help biologists classify major animal phyla during evolutionary studies. Understanding determinate development is crucial for studying developmental biology and congenital defects. Cell fate determination dictates how complex tissues eventually form from a single fertilized egg. Spiral and indeterminate is a combination that does not typically occur in standard developmental biology models. Radial and indeterminate cleavage is characteristic of deuterostomes like echinoderms and vertebrates. Radial and determinate represents an incorrect pairing of cleavage characteristics and animal lineages.
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