DEVELOPMENT BILOGY-I

1. NAME: ANSARI KAUSAR MOHD KHALID
ID NO: 7763
ROLL NO: 08
CLASS: MSC-I
SUBJECT: PAPER-2 (DEVELOPMENT BIOLOGY)
DEPARTMENT OF ZOOLOGY

2. TOPIC:
Mosaic and regulative
development

3. MOSAIC DEVELOPMENT-
❖ The idea of Mosaic development was conceived by A.Waismann in 1880s
❖ He explained nucleus of the zygote contained a number of special factors of
Determinants which were distributed unequally to the daughter cells after cleavage of
the zygote and control the future development of these cells.
❖ The experimental evidence for the Mosaic development was given by Wilhelm Roux in
1888, who was known as FATHER OF EXPERIMENTAL EMBRYOLOGY.
❖ He performed experiments on frogs egg. After first cleavage of fertilization of frog egg,
Roux killed one of the two blastomeres with hot needle and observed that the remaining
live blastomere developed into a well formed.
❖ THE DEVELOPMENT IS CONTROLLED BY THE INTRINSIC FEATURES
ARE CALLED AS MOSAIC THEORY OF DEVELOPMENT OR
DETERMINATE DEVELOPMENT

5. REGULATIVE DEVELOPMENT-
❖ It was proposed by Hans Driesch in 1891 after
conducting experiments on the fertilized egg of sea
urchin as they could be easily explored and are
transparent.
❖ The regulative theory is in contrast to the idea of
mosaic theory of development.
❖ He observed that the blastomeres of sea urchin when
separated from each other at two cell stage,
developed into two complete larvae.
❖ Each cell undergo in conditional specification.
❖ The fate of cell is governed by its interaction with
other cell.
❖ IF THE DEVELOPMENT IS CONTROLLED
BY INDUCTIVE SIGNAL IS CALLED AS THE
REGULATIVE THEORY OF DEVELOPMENT

6. ❏ DREICH CONCLUDE THAT :
➔ The prospective potential of an isolated blastomeres is greater than the blastomeres
actual prospective fate.
➔ Sea urchin embryo is an “harmonious equipotential system”. because all its
potentially independent parts interacted together to form a single organism.
REGULATIVE DEVELOPMENT-

7. CELL SPECIFICATION:
AUTONOMOUS
SPECIFICATION

8. CELL SPECIFICATION:
The fate of a cell or a tissue is said to be specified when it is capable of differentiating
autonomously

9. AUTONOMOUS SPECIFICATION:
The first is called autonomous specification. In this case, if a
particular blastomere is removed from an embryo early in its
development, that isolated blastomere will produce the same cells
that it would have made if it were still part of the embryo.
Autonomous specification gives rise to a pattern of development
referred to as Mosaic development.
Invertebrate embryos, especially those of molluscs, annelids, and
tunicates, often use autonomous specification to determine the fate
of their cells.In these embryos, morphogenetic determinants are
placed in different regions of the egg cytoplasm and are
apportioned to the different cells as the embryo divides. These
morphogenetic determinants specify the cell type.

10. Autonomous specification (mosaic development). (A-C) Differentiation of
trophoblast (ciliated) cells of the mollusc Patella. (A) 16-cell stage seen from
the side; the presumptive trophoblast cells are shaded. (B) 48-cell stage. (C)
Ciliated larval stage, seen from the animal pole. (D-G) Differentiation of a
Patella trophoblast cell isolated from the 16-cell stage and cultured in vitro.
(E, F)Results of the first and second divisions in culture. (G) Ciliated products
of (F). Even in isolated culture, the cells divide and become ciliated at the
correct time.

11. REFERENCE:
❖ DEVELOPMENT BIOLOGY-SCOTT GILBERT-8TH EDITION
,2006
❖ INVERTEBRATE ZOOLOGY

12. THANK YOU ☺