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Questions and Answers
Weismann’s theory of determinative ______ are distributed unequally.
Weismann’s theory of determinative ______ are distributed unequally.
factors
The fate of each cell is predetermined by the ______ it receives.
The fate of each cell is predetermined by the ______ it receives.
factors
Cytoplasmic components are floating during ______.
Cytoplasmic components are floating during ______.
cleavage
Weismann became a ______ as he developed his theories in the 1880s.
Weismann became a ______ as he developed his theories in the 1880s.
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Weismann is famous for the elucidation of the germ ______ theory.
Weismann is famous for the elucidation of the germ ______ theory.
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Factors in the nucleus are distributed ______ to cleavage partitions.
Factors in the nucleus are distributed ______ to cleavage partitions.
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Weismann assumed that different ______ are directed to future development of daughter cells.
Weismann assumed that different ______ are directed to future development of daughter cells.
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Cleavage partitions different ______ to daughter cells.
Cleavage partitions different ______ to daughter cells.
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If you tie a loop of baby hair and tighten slowly to clearage each separate ______, both develop normally.
If you tie a loop of baby hair and tighten slowly to clearage each separate ______, both develop normally.
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Driesch concluded that sea urchin cleavage is ______.
Driesch concluded that sea urchin cleavage is ______.
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The phenomenon where half regular size – entelechy – is considered from a ______ perspective.
The phenomenon where half regular size – entelechy – is considered from a ______ perspective.
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TH Morgan repeated Driesch’s sea urchin experiment – but this time on ______.
TH Morgan repeated Driesch’s sea urchin experiment – but this time on ______.
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Both blastomeres developed into complete ______.
Both blastomeres developed into complete ______.
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Mosaic vs ______ development refers to different strategies of cell fate determination.
Mosaic vs ______ development refers to different strategies of cell fate determination.
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______ development establishes cell fate later, via cell-cell interactions.
______ development establishes cell fate later, via cell-cell interactions.
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Mosaic or determinative development establishes cell fate at each ______ division.
Mosaic or determinative development establishes cell fate at each ______ division.
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The transition from maternal control of development to ______ control is most evident in animals with large eggs.
The transition from maternal control of development to ______ control is most evident in animals with large eggs.
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During the mid-blastula transition, many maternal mRNAs are actively ______.
During the mid-blastula transition, many maternal mRNAs are actively ______.
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The introduction of gap phases, G1 and G2, occurs during the slowing of the ______ cycle.
The introduction of gap phases, G1 and G2, occurs during the slowing of the ______ cycle.
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The process of counting cleavage divisions may control the timing of the ______.
The process of counting cleavage divisions may control the timing of the ______.
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Asynchronous divisions occur during the transition from early to late ______.
Asynchronous divisions occur during the transition from early to late ______.
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Roux’s evidence for ______ development indicates a specific mechanism.
Roux’s evidence for ______ development indicates a specific mechanism.
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Frog cleavage divisions are described as strictly ______.
Frog cleavage divisions are described as strictly ______.
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The undamaged cell survives while the ______ cell is destroyed.
The undamaged cell survives while the ______ cell is destroyed.
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Roux's conclusion suggests no cells will form resembling a normal ______.
Roux's conclusion suggests no cells will form resembling a normal ______.
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In a mosaic development, the fate of the cells is ______ determined.
In a mosaic development, the fate of the cells is ______ determined.
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The cell can divide normally as long as it is ______.
The cell can divide normally as long as it is ______.
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If damaged, the cell may result in ______ formed structures.
If damaged, the cell may result in ______ formed structures.
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Roux's evidence refutes the idea that frog cleavage leads to ______ characteristics.
Roux's evidence refutes the idea that frog cleavage leads to ______ characteristics.
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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 ______.
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 ______.
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Transcription of genes that promote destruction of ______ leads to even longer gaps in cell division.
Transcription of genes that promote destruction of ______ leads to even longer gaps in cell division.
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Compaction in mammals results in the formation of a solid ball of cells known as a ______.
Compaction in mammals results in the formation of a solid ball of cells known as a ______.
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High level expression of E-cadherin, a cell-cell adhesion molecule, is crucial for cells to associate tightly with each ______.
High level expression of E-cadherin, a cell-cell adhesion molecule, is crucial for cells to associate tightly with each ______.
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During compaction, cells on the inside of the morula will contribute to the ______.
During compaction, cells on the inside of the morula will contribute to the ______.
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Compaction begins with the formation of a ______ layer that helps in the organization of the cells.
Compaction begins with the formation of a ______ layer that helps in the organization of the cells.
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The completion of cleavage divisions leads to the blastula stage, also known as ______ or blastocyst depending on the organism.
The completion of cleavage divisions leads to the blastula stage, also known as ______ or blastocyst depending on the organism.
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In most cases, the result of these divisions is an asymmetric embryo, with cells at different locations giving rise to different ______.
In most cases, the result of these divisions is an asymmetric embryo, with cells at different locations giving rise to different ______.
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The mouse blastocyst sits on top of yolk in a structure surrounded by a ______ layer.
The mouse blastocyst sits on top of yolk in a structure surrounded by a ______ layer.
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Cells undergo ______ to prepare for the next stage of development, gastrulation.
Cells undergo ______ to prepare for the next stage of development, gastrulation.
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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.
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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.
