BSC-2011 Lecture Notes - Lecture 6: Deuterostome, Blastula, Blastocoel
Document Summary
The pattern of cleavage planes is species-specific and critical to normal development because cleavage partitions cytoplasmic maternal determinants. These maternal determinants trigger early differential gene expression and ultimately cell differentiation. Determination can be achieved via different maternal cytoplasmic determinants that are asymmetrically distributed during cell division and permit differential gene expression in daughter cells. Determination: a process by which a cell differentiates and ultimately meets its fate by expressing a unique set of genes. An unfertilized egg has a non-random distribution of maternal determinants in the egg cytoplasm. Sea urchin microlecithal (small yolk) egg type with holoblastic cleavage. Frog mesolecithal egg type (moderate yolk) with holoblastic cleavage. Chicken macrolecithal egg type (large yolk) with meroblastic cleavage. Morula stage same size but egg divided into many cells. Blastula stage- beginning of getting true animal form. An undifferentiated mass of embryonic cells begin to take shape.
