Questions and Answers
Weismann’s theory of determinative ______ are distributed unequally.
factors
The fate of each cell is predetermined by the ______ it receives.
factors
Cytoplasmic components are floating during ______.
cleavage
Weismann became a ______ as he developed his theories in the 1880s.
Signup and view all the answers
Weismann is famous for the elucidation of the germ ______ theory.
Signup and view all the answers
Factors in the nucleus are distributed ______ to cleavage partitions.
Signup and view all the answers
Weismann assumed that different ______ are directed to future development of daughter cells.
Signup and view all the answers
Cleavage partitions different ______ to daughter cells.
Signup and view all the answers
If you tie a loop of baby hair and tighten slowly to clearage each separate ______, both develop normally.
Signup and view all the answers
Driesch concluded that sea urchin cleavage is ______.
Signup and view all the answers
The phenomenon where half regular size – entelechy – is considered from a ______ perspective.
Signup and view all the answers
TH Morgan repeated Driesch’s sea urchin experiment – but this time on ______.
Signup and view all the answers
Both blastomeres developed into complete ______.
Signup and view all the answers
Mosaic vs ______ development refers to different strategies of cell fate determination.
Signup and view all the answers
______ development establishes cell fate later, via cell-cell interactions.
Signup and view all the answers
Mosaic or determinative development establishes cell fate at each ______ division.
Signup and view all the answers
The transition from maternal control of development to ______ control is most evident in animals with large eggs.
Signup and view all the answers
During the mid-blastula transition, many maternal mRNAs are actively ______.
Signup and view all the answers
The introduction of gap phases, G1 and G2, occurs during the slowing of the ______ cycle.
Signup and view all the answers
The process of counting cleavage divisions may control the timing of the ______.
Signup and view all the answers
Asynchronous divisions occur during the transition from early to late ______.
Signup and view all the answers
Roux’s evidence for ______ development indicates a specific mechanism.
Signup and view all the answers
Frog cleavage divisions are described as strictly ______.
Signup and view all the answers
The undamaged cell survives while the ______ cell is destroyed.
Signup and view all the answers
Roux's conclusion suggests no cells will form resembling a normal ______.
Signup and view all the answers
In a mosaic development, the fate of the cells is ______ determined.
Signup and view all the answers
The cell can divide normally as long as it is ______.
Signup and view all the answers
If damaged, the cell may result in ______ formed structures.
Signup and view all the answers
Roux's evidence refutes the idea that frog cleavage leads to ______ characteristics.
Signup and view all the answers
By cycle 11 overall cyclin levels drop enough to get slowing of the cell cycle leading to a longer gap between cell divisions allowing some genes to be ______.
Signup and view all the answers
Transcription of genes that promote destruction of ______ leads to even longer gaps in cell division.
Signup and view all the answers
Compaction in mammals results in the formation of a solid ball of cells known as a ______.
Signup and view all the answers
High level expression of E-cadherin, a cell-cell adhesion molecule, is crucial for cells to associate tightly with each ______.
Signup and view all the answers
During compaction, cells on the inside of the morula will contribute to the ______.
Signup and view all the answers
Compaction begins with the formation of a ______ layer that helps in the organization of the cells.
Signup and view all the answers
The completion of cleavage divisions leads to the blastula stage, also known as ______ or blastocyst depending on the organism.
Signup and view all the answers
In most cases, the result of these divisions is an asymmetric embryo, with cells at different locations giving rise to different ______.
Signup and view all the answers
The mouse blastocyst sits on top of yolk in a structure surrounded by a ______ layer.
Signup and view all the answers
Cells undergo ______ to prepare for the next stage of development, gastrulation.
Signup and view all the answers
Study Notes
Weismann’s Theory of Determinative Development
- Determinative factors are distributed unequally during cleavage, influencing each cell's fate.
- Cell fates are predetermined based on cytoplasmic components received during cleavage.
- Weismann introduced the germ plasm theory, focusing on the asymmetrical distribution of factors to daughter cells.
Mosaic Development
- Mosaic development indicates that specific cell fates are established at the time of cell division.
- Evidence from Roux showed that damaging one cell of a two-cell embryo resulted in no normal development of the damaged cell, confirming mosaic nature.
- Frog cleavage demonstrates mosaic characteristics, but experiments show that normal development occurs even with disrupted conditions.
Driesch’s Evidence for Regulative Development
- Driesch showed that sea urchin embryos could develop normally even when half was separated, suggesting that development could adapt.
- The concept of entelechy suggests a vital force is at play, influencing organism development.
- Variances in development between species may be due to different strategies for cell fate determination or experimental method discrepancies.
Experimental Findings by T.H. Morgan
- Morgan’s experiments demonstrated that both blastomeres from frog eggs can develop into complete embryos when separated.
- Indicates that sea urchins and frogs may adaptively regulate their development despite initial differences noted by Driesch.
Mosaic vs. Regulative Development
- Regulative development relies on cell-cell interactions establishing cell fates later, dominating in late cleavage divisions.
- Most organisms employ a mixed strategy that includes both mosaic and regulative development, with C. elegans exemplifying mostly mosaic development.
Mid-Blastula Transition (MBT)
- Shift from maternal to zygotic control of development occurs during the MBT, significant in species with large eggs.
- Early cleavage lacks transcription and occurs rapidly with no gap phases.
- MBT introduces transcription, asynchronous cell divisions, and degradation of maternal mRNAs, allowing new genes to be expressed.
Mechanism of MBT
- Timing of MBT may depend on several factors, including cleavage division counts and material depletion.
- A drop in cyclin levels leads to prolonged cell cycle gaps, permitting gene transcription necessary for development and maternal mRNA degradation.
Compaction in Mammals
- Compaction leads to a solid ball of cells (morula) transitioning to the blastocyst stage.
- High expression of E-cadherin enhances cell adhesion, promoting tight cell associations and distinction of inner and outer cell types.
- Inner cells contribute to the embryo, while outer cells form extra-embryonic structures and the placenta.
Blastula Stage
- Known as blastoderm or blastocyst, depending on the organism, it represents the completion of cleavage divisions before gastrulation.
- Typically results in an asymmetric embryo, where cells in varying positions develop into different cell types.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz delves into Weismann's theory of determinative factors and their unequal distribution in future generations. Explore the concepts of cleavage and hereditary determinants through a series of questions designed to test your understanding of this foundational biological theory.
