SEM_03_cleavage
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Questions and Answers

What is cleavage in the context of embryology?

  • The termination of blastocyst formation
  • The fusion of chimaeras and duplication of embryos
  • The initial series of rapid mitotic divisions dividing the zygote into blastomeres (correct)
  • The process of cell differentiation leading to specialized cell types

    • What is the significance of the morula in embryonic development?

  • It marks the beginning of cell differentiation
  • It is the precursor to the blastocyst stage (correct)
  • It leads to the formation of blastomeres
  • It is the stage where cleavage terminates

    • What role does the trophoblast play in embryonic development?

  • Becoming part of the inner cell mass
  • Contributing to the formation of extraembryonic membranes (correct)
  • Formation of the blastomeres
  • Differentiation into specialized cell types

    • What is the main mechanism of cellular differentiation?

    <p>Induction</p> Signup and view all the answers

    What is the starting place for understanding the process of differentiation?

    <p>Nucleus of the original zygote</p> Signup and view all the answers

    What is the role of proteins synthesis in cell differentiation?

    <p>It controls gene expression for specific proteins</p> Signup and view all the answers

    What makes a liver cell different from a skin or muscle cell?

    <p>Different combination of activated and inactivated genes</p> Signup and view all the answers

    What do maternal genes gradually activate during embryonic development?

    <p>Segmentation genes</p> Signup and view all the answers

    What is the primary method to control what type and how much of each protein is expressed in prokaryotic cells?

    <p>Transcriptional level</p> Signup and view all the answers

    What does epigenomics study in a specific cell type?

    <p>Epigenetic marks in DNA</p> Signup and view all the answers

    What defines the range of different cell types a cell can become?

    <p>Genetic code</p> Signup and view all the answers

    At what stage are cells totipotent, having the potential to develop into a complete organism?

    <p>2-4 cell stage</p> Signup and view all the answers

    What is the process by which more specialized cells develop from less specialized cell types called?

    <p>Cell differentiation</p> Signup and view all the answers

    What ultimately regulates cell differentiation through differential gene expression?

    <p>Genetic control</p> Signup and view all the answers

    Which type of cells can differentiate into a variety of tissues but not all?

    <p>Multipotent stem cells</p> Signup and view all the answers

    What describes the range of different cell types that a cell can become?

    <p>Cell potency</p> Signup and view all the answers

    Which stage is characterized by a stable change in cell organization and irreversible fate for determined cells?

    <p>&quot;Irreversible stage&quot;</p> Signup and view all the answers

    What describes the process of progressive restrictions in the developmental potentials of cells?

    <p>Cell determination</p> Signup and view all the answers

    What is ultimately responsible for forming all the embryo structures during differentiation?

    <p>Genetic control</p> Signup and view all the answers

    What term is used to describe the reversible state of being committed to a certain fate before cell determination?

    <p>Cell specification</p> Signup and view all the answers

    What describes the process by which proteins are gradually specialized within a common genome during differentiation?

    <p>Protein synthesis</p> Signup and view all the answers

    At which stage does fertilization occur in the oviduct?

    <p>Blastocyst stage</p> Signup and view all the answers

    What type of cleavage pattern is present in bird eggs?

    <p>Meroblastic cleavage</p> Signup and view all the answers

    What is the main characteristic of a hatched mammalian blastocyst?

    <p>Hollow and fluid-filled structure</p> Signup and view all the answers

    What is the result of mammalian blastomeres dividing asynchronously?

    <p>Odd-numbered cell stages</p> Signup and view all the answers

    What influences the cleavage pattern in bird eggs?

    <p>Yolk-centered structure</p> Signup and view all the answers

    In which stage does the blastodisc transform into a two-layered blastula in birds?

    <p>Blastocyst stage</p> Signup and view all the answers

    What type of embryo is produced by reptiles and birds due to meroblastic cleavage?

    <p>Disk-shaped embryo</p> Signup and view all the answers

    At what stage does the mammalian blastocyst release from the zona pellucida?

    <p>After reaching the uterus</p> Signup and view all the answers

    What happens to hatched blastocysts before implantation in mammals?

    <p>Rapid growth phase begins</p> Signup and view all the answers

    What is the characteristic of reptile and bird embryos produced due to meroblastic cleavage?

    <p>Disk-shaped structure</p> Signup and view all the answers

    Where does fertilization occur in mammals?

    <p>In the ampulla of the oviduct</p> Signup and view all the answers

    What type of cleavage produces blastomeres of approximately equal size?

    <p>Holoblastic cleavage</p> Signup and view all the answers

    What determines the pattern and speed of cleavage?

    <p>Amount and distribution of yolk in the egg</p> Signup and view all the answers

    What happens to blastomeres with each successive division?

    <p>They become smaller</p> Signup and view all the answers

    What is the result of meroblastic cleavage?

    <p>Formation of a discoidal morula</p> Signup and view all the answers

    What is the characteristic of superficial meroblastic cleavage?

    <p>Produces a layer of cells around a central mass of yolk</p> Signup and view all the answers

    What is the outcome of unequal holoblastic cleavage?

    <p>Produces blastomeres of unequal size</p> Signup and view all the answers

    What is the result of compaction in the morula stage?

    <p>Surface blastomeres become flattened and form tight junctions</p> Signup and view all the answers

    What is the characteristic of holoblastic cleavage?

    <p>Complete division of the egg</p> Signup and view all the answers

    What is the primary mechanism of cellular differentiation?

    <p>Progressive restriction in developmental potentials</p> Signup and view all the answers

    Which stage marks the termination of cleavage in mammals?

    <p>Blastocyst</p> Signup and view all the answers

    What is the characteristic of superficial meroblastic cleavage?

    <p>Asynchronous division of blastomeres</p> Signup and view all the answers

    What is the outcome of unequal holoblastic cleavage?

    <p>Development of blastomeres of unequal size</p> Signup and view all the answers

    During which stage does the blastodisc transform into a two-layered blastula in bird embryos?

    <p>Blastocyst stage</p> Signup and view all the answers

    What is the characteristic of superficial meroblastic cleavage?

    <p>Discoidal cleavage resulting in a single-layered blastodisc</p> Signup and view all the answers

    What happens to hatched mammalian blastocysts before implantation?

    <p>They undergo rapid growth</p> Signup and view all the answers

    What is the result of meroblastic cleavage?

    <p>Disk-shaped embryo with upper epiblast and lower hypoblast</p> Signup and view all the answers

    What type of cleavage produces blastomeres of approximately equal size?

    <p>Holoblastic cleavage</p> Signup and view all the answers

    What is responsible for influencing the cleavage pattern in bird eggs?

    <p>Yolk-centered structure</p> Signup and view all the answers

    Where does fertilization occur in mammals?

    <p>Ampulla of the oviduct</p> Signup and view all the answers

    What is the main characteristic of a hatched mammalian blastocyst?

    <p>Fluid-filled spherical structure</p> Signup and view all the answers

    "At what stage are cells totipotent, having the potential to develop into a complete organism?"

    <p>Morula stage</p> Signup and view all the answers

    "What determines the pattern and speed of cleavage?"

    <p>Yolk-centered structure</p> Signup and view all the answers

    "What role does the trophoblast play in embryonic development?"

    <p>Development of placental membranes</p> Signup and view all the answers

    "What is ultimately responsible for forming all the embryo structures during differentiation?"

    <p>Inner cell mass</p> Signup and view all the answers

    Which process involves the gradual specialization of the protein contents of a cell, eventually leading to the development of a specialized cell type?

    <p>Cell specialization</p> Signup and view all the answers

    At which stage are cells totipotent, capable of developing into a complete organism, including the placenta?

    <p>Morula stage</p> Signup and view all the answers

    What term describes the irreversible stage in cell development, implying a stable change in cell organization?

    <p>Cell determination</p> Signup and view all the answers

    What plays a role in regulating cell differentiation through differential gene expression?

    <p>Both genetic control and environmental influences</p> Signup and view all the answers

    What is the primary method to control what type and how much of each protein is expressed in eukaryotic cells?

    <p>Promoters and enhancers</p> Signup and view all the answers

    What is indicated by the fate of cells, as observed by labeling and observing which structures they become part of?

    <p>Cell potency</p> Signup and view all the answers

    What is the process where less specialized cells develop into more specialized cell types?

    <p>Cell specialization</p> Signup and view all the answers

    What do totipotent stem cells originate from?

    <p>Zygote</p> Signup and view all the answers

    What can gradual specialization of the protein contents of a cell lead to?

    <p>Organ formation</p> Signup and view all the answers

    What is the process that is controlled by mechanisms promoting or stopping cell divisions at specific moments?

    <p>Cell division</p> Signup and view all the answers

    What determines the potential of individual cells as development proceeds?

    <p>Cell potency</p> Signup and view all the answers

    What is the result of differences in the production and suppression of genes during embryonic development?

    <p>Cell differentiation</p> Signup and view all the answers

    What is the primary method to control what type and how much of each protein is expressed in eukaryotic cells?

    <p>Transcriptional regulation</p> Signup and view all the answers

    Which type of genes are essential for determining the anatomical identity of different body parts along the anterior/posterior axis?

    <p>Homeotic genes</p> Signup and view all the answers

    What contributes to gene expression and plays a role in cell differentiation and embryo development through epigenetic modifications?

    <p>DNA methylation</p> Signup and view all the answers

    What is the outcome of unequal holoblastic cleavage?

    <p>Formation of different cell types</p> Signup and view all the answers

    Which genes control the gene expression during the early stages of pattern formation in the embryo?

    <p>Hox genes</p> Signup and view all the answers

    What regulates the expression of specific proteins by controlling the activation/repression of genes?

    <p>Transcription factors</p> Signup and view all the answers

    Which process involves the irreversible commitment of a cell to a specific fate before cell determination?

    <p>Cell specification</p> Signup and view all the answers

    What controls gene expression by affecting the development of an organism from embryonic stages to adult life?

    <p>Both internal and external cues</p> Signup and view all the answers

    What contributes to gene expression and plays a role in cell differentiation through modifications such as histone acetylation?

    <p>Histone methylation</p> Signup and view all the answers

    Which type of cleavage produces blastomeres of approximately equal size?

    <p>Holoblastic cleavage</p> Signup and view all the answers

    What type of genes are responsible for forming the basic three-dimensional layout of the early embryo's body?

    <p>Hox genes</p> Signup and view all the answers

    In eukaryotic cells, what process involves controlling gene expression at multiple levels such as pre-transcriptional, transcriptional, post-transcriptional, and post-translational regulation?

    <p>Transcriptional regulation</p> Signup and view all the answers

    What type of cleavage is the complete division of the egg, producing blastomeres of approximately equal size?

    <p>Holoblastic cleavage</p> Signup and view all the answers

    What is the characteristic of superficial meroblastic cleavage?

    <p>Layer of cells around a central mass of yolk</p> Signup and view all the answers

    What stage ends with the formation of a blastocyst or blastula, which is a hollow structure with a central cavity?

    <p>Morula stage</p> Signup and view all the answers

    What defines the range of different cell types a cell can become?

    <p>Potential of individual cells as development proceeds</p> Signup and view all the answers

    What is responsible for influencing the cleavage pattern in bird eggs?

    <p>Amount and distribution of yolk in the egg</p> Signup and view all the answers

    What is the result of compaction in the morula stage?

    <p>Flattening and formation of tight junctions</p> Signup and view all the answers

    Which type of development is characterized by the uneven distribution of cytoplasmic determinants into distinct daughter cells, leading to the disappearance of cell totipotence?

    <p>Mosaic development</p> Signup and view all the answers

    What is the term for the process where cytoplasmic determinants are equally distributed in newly created cells, as observed in some animals?

    <p>Regulative development</p> Signup and view all the answers

    What characteristic is exhibited by the future embryo in mosaic development due to the uneven distribution of cytoplasmic determinants?

    <p>Distinct regions with specific cytoplasmic determinants</p> Signup and view all the answers

    What effect does the uneven distribution of cytoplasmic determinants have on the cell totipotence during segmentation in mosaic development?

    <p>Disappears very quickly</p> Signup and view all the answers

    What are morphogens?

    <p>Intercellular signals involved in cell communication during embryonic development</p> Signup and view all the answers

    How do morphogens act in creating concentration gradients?

    <p>They act with high concentrations near the source and low concentrations farther away</p> Signup and view all the answers

    What does the formation of chimaeras involve?

    <p>Exchange of cells and genetic material during development</p> Signup and view all the answers

    Which type of twins are formed when a single fertilized egg splits into two?

    <p>Identical twins</p> Signup and view all the answers

    What is the characteristic of conjoined identical twins?

    <p>Physical connection resulting from blastomeres partially separating</p> Signup and view all the answers

    What determines the success of surgical separation of conjoined twins?

    <p>Degree of union and the surgical team's skill</p> Signup and view all the answers

    What are monozygotic twins also known as?

    <p>Identical twins</p> Signup and view all the answers

    What is the characteristic of different types of union in conjoined twins?

    <p>Varying degrees of physical connection</p> Signup and view all the answers

    What determines the potential of individual cells as development proceeds?

    <p>Genetic material exchange during development</p> Signup and view all the answers

    What defines the range of different cell types a cell can become?

    <p>Morphogens acting with concentration gradients</p> Signup and view all the answers

    What ultimately forms all the embryo structures during differentiation?

    <p>Intercellular signals involved in cell communication during embryonic development</p> Signup and view all the answers

    Which genes control the gene expression during the early stages of pattern formation in the embryo?

    <p>Maternal genes</p> Signup and view all the answers

    What term describes the process in which one embryonic region influences another through secreted substances, causing cellular differentiation and tissue development?

    <p>Induction</p> Signup and view all the answers

    Which factor is responsible for numerous fundamental inductions and is mediated by signaling factors such as Fgf, Wnt, Tgf, and Hh families?

    <p>Induction</p> Signup and view all the answers

    What role do organizer centers play in developmental biology?

    <p>Instructing adjacent cells into specific states</p> Signup and view all the answers

    Which structure in amphibian embryos is responsible for the formation of the notochord and neural tube?

    <p>Dorsal blastopore lip</p> Signup and view all the answers

    What term describes the development of shape and the organization of functional groups of organs, achieved through complex interactions of cells during pattern formation?

    <p>Morphogenesis</p> Signup and view all the answers

    Which process defines the specific spatial organization of organs and tissues?

    <p>Morphogenesis</p> Signup and view all the answers

    What is the primary method to control what type and how much of each protein is expressed in prokaryotic cells?

    <p>Cytoplasmic determinants</p> Signup and view all the answers

    Which type of genes are essential for determining the anatomical identity of different body parts along the anterior/posterior axis?

    <p>Morphogenetic genes</p> Signup and view all the answers

    Which stage is characterized by a stable change in cell organization and irreversible fate for determined cells?

    <p>Gastrulation stage</p> Signup and view all the answers

    What is the result of compaction in the morula stage?

    <p>Formation of trophectoderm</p> Signup and view all the answers

    What happens to hatched blastocysts before implantation in mammals?

    <p>They hatch from the zona pellucida</p> Signup and view all the answers

    What is responsible for influencing the cleavage pattern in bird eggs?

    <p>Cytoplasmic determinants</p> Signup and view all the answers

    What is the term for fraternal twins who develop independently during the same pregnancy?

    <p>Dizygotic twins</p> Signup and view all the answers

    What is the term for the condition where there are adhesions between the placentas of dizygotic twins in cows?

    <p>Freemartin syndrome</p> Signup and view all the answers

    What is the term for asymmetrical or unequal identical twins that occur when one embryo maintains dominant development at the expense of the other?

    <p>Parasitic twins</p> Signup and view all the answers

    What do parasitic twins represent in terms of the processes that also produce vanishing and conjoined twins?

    <p>A continuum</p> Signup and view all the answers

    What is the term for the process where a twin embryo begins developing in utero but does not fully separate?

    <p>Parasitic twinning</p> Signup and view all the answers

    What is the term for identical or monozygotic twins that may or may not share the same amniotic sac?

    <p>Monoamniotic twins</p> Signup and view all the answers

    What is the term for a rudimentary twin that is usually found sharing the same placenta with a normal twin?

    <p>Amorphous twin</p> Signup and view all the answers

    What is the term for a condition where conjoined twins begin developing in utero and one embryo maintains dominant development at the expense of the other?

    <p>Parasitic twinning</p> Signup and view all the answers

    What is the primary effect of uneven distribution of cytoplasmic determinants into distinct daughter cells during segmentation?

    <p>Mosaic development</p> Signup and view all the answers

    What is the term for the type of development in which cytoplasmic determinants are equally distributed in the newly created cells?

    <p>Regulative development</p> Signup and view all the answers

    What happens to cell totipotence if cytoplasmic determinants become unevenly distributed into the daughter cells from the first divisions?

    <p>It disappears very quickly during segmentation</p> Signup and view all the answers

    What is the consequence of mosaic development due to the uneven distribution of cytoplasmic determinants into distinct daughter cells?

    <p>Distinct cytoplasmic determinants in distinct cells</p> Signup and view all the answers

    In which type of species are fraternal twins more commonly found?

    <p>Monotocous species</p> Signup and view all the answers

    What is the result of differences in the production and suppression of genes during embryonic development?

    <p>Formation of chimaeras</p> Signup and view all the answers

    What is the term for identical or monozygotic twins that may or may not share the same amniotic sac?

    <p>Parasitic twins</p> Signup and view all the answers

    What is the characteristic of superficial meroblastic cleavage?

    <p>Uneven distribution of cytoplasmic determinants</p> Signup and view all the answers

    What is the term for a rudimentary twin that is usually found sharing the same placenta with a normal twin?

    <p>Parasitic twin</p> Signup and view all the answers

    What contributes to gene expression and plays a role in cell differentiation and embryo development through epigenetic modifications?

    <p>Morphogens</p> Signup and view all the answers

    What stage marks the termination of cleavage in mammals?

    <p>Morula stage</p> Signup and view all the answers

    What do parasitic twins represent in terms of the processes that also produce vanishing and conjoined twins?

    <p>A continuum between vanishing and conjoined twins</p> Signup and view all the answers

    What is the term for the process in which one embryonic region influences another through secreted substances, causing cellular differentiation and tissue development?

    <p>Induction</p> Signup and view all the answers

    Which factor is responsible for forming concentration gradients and mediating numerous fundamental inductions in embryonic development?

    <p>Fgf family</p> Signup and view all the answers

    What is the term for the group of cells with the ability to instruct adjacent cells into specific states, playing a crucial role in developmental biology?

    <p>Organizer centres</p> Signup and view all the answers

    What is the term for the process that defines the specific spatial organization of organs and tissues?

    <p>Morphogenesis</p> Signup and view all the answers

    What is the term for a substance secreted by one group of cells altering the development of another group, often leading to instructive changes in cellular commitments?

    <p>Induction</p> Signup and view all the answers

    What plays a crucial role in the formation of the notochord and neural tube in amphibian embryos?

    <p>Organizer centres</p> Signup and view all the answers

    What type of cells have the ability to become inducing tissues, leading to a cascade of embryonic inductions that shape the body plan?

    <p>Inducing tissues</p> Signup and view all the answers

    "Cytoplasmic determinants" affect cell fate decisions through gene activities in specific cells. What are cytoplasmic determinants?

    <p>&quot;Cytoplasmic determinants&quot; are components in the egg or zygote's cytoplasm that affect cell fate decisions.</p> Signup and view all the answers

    "Morphogenesis" is achieved through complex interactions of cells during pattern formation. What is morphogenesis?

    <p>&quot;Morphogenesis&quot; is the development of shape and organization of functional groups of organs.</p> Signup and view all the answers

    "Regulative development" means that cells in early stages can lead to complete individuals when separated or fused. What is regulative development?

    <p>&quot;Regulative development&quot; is when cells in early stages can lead to complete individuals when separated or fused.</p> Signup and view all the answers

    What does cytoplasmic determinants affect through gene activities in specific cells?

    <p>Cell fate decisions</p> Signup and view all the answers

    What are morphogens?

    <p>Intercellular signals providing positional information to target cells</p> Signup and view all the answers

    What is the consequence of mosaic development due to the uneven distribution of cytoplasmic determinants into distinct daughter cells?

    <p>Disappearance of cell totipotence</p> Signup and view all the answers

    What term is used to describe the reversible state of being committed to a certain fate before cell determination?

    <p>Prepatterned</p> Signup and view all the answers

    What is the characteristic of different types of union in conjoined twins?

    <p>Physically connected twins</p> Signup and view all the answers

    What is the term for a condition where conjoined twins begin developing in utero and one embryo maintains dominant development at the expense of the other?

    <p>Twin embolization syndrome</p> Signup and view all the answers

    What contributes to gene expression and plays a role in cell differentiation through modifications such as histone acetylation?

    <p>Epigenetic modifications</p> Signup and view all the answers

    What is the characteristic of conjoined identical twins?

    <p>Genetically identical cell populations</p> Signup and view all the answers

    Study Notes

    • Maternal proteins and mRNAs control early embryonic cleavages in the zygote.

    • Cleavage divisions are rapid mitotic divisions, increasing the number of cells without increasing cytoplasmic mass.

    • The blastomeres become smaller with each successive division, resulting in a collection of average size cells.

    • The amount and distribution of yolk in the egg determine the pattern and speed of cleavage.

    • Holoblastic cleavage is the complete division of the egg, producing blastomeres of approximately equal size.

    • Unequal holoblastic cleavage produces blastomeres of unequal size due to the presence of a large yolk mass.

    • Meroblastic cleavage is incomplete division due to the presence of yolk and results in the formation of a discoidal morula.

    • Superficial meroblastic cleavage produces a layer of cells around a central mass of yolk.

    • The morula is a solid collection of cells that undergoes compaction, resulting in surface blastomeres becoming flattened and forming tight junctions.

    • The morula stage ends with the formation of a blastocyst or blastula, which is a hollow structure with a central cavity.

    • The nucleus of a mature organism's cell contains all the genetic instructions (DNA) to make all the cell types, and the process of differentiation involves the activation or inactivation of specific genes to produce the unique protein collection for each cell type.

    • Cells in a complex multicellular organism contain the same DNA, but different cell types are distinguished by the combination of genes that are expressed or repressed.

    • Gene expression is regulated by both internal and external cues, which affect the development of an organism from embryonic stages to adult life.

    • The formation of cells, tissues, and organs is under the control of various types of genes, including maternal genes, segmentation genes, and homeotic genes.

    • The early embryo's body has a basic three-dimensional layout with dorsal, ventral, cranial, and caudal axes, and a similar family of genes, such as Hox genes, controls the gene expression during the early stages of pattern formation.

    • Homeotic genes are essential for determining the anatomical identity of different body parts along the anterior/posterior axis and include a nearly identical DNA sequence called the homeobox region.

    • In eukaryotic cells, the control of gene expression is a multi-level process that involves pre-transcriptional, transcriptional, post-transcriptional, and post-translational regulation.

    • Transcription factors that activate/repress genes are crucial for controlling the expression of specific proteins.

    • Epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNA, contribute to gene expression and thus play a role in cell differentiation and embryo development.

    • Maternal proteins and mRNAs control early embryonic cleavages in the zygote.

    • Cleavage divisions are rapid mitotic divisions, increasing the number of cells without increasing cytoplasmic mass.

    • The blastomeres become smaller with each successive division, resulting in a collection of average size cells.

    • The amount and distribution of yolk in the egg determine the pattern and speed of cleavage.

    • Holoblastic cleavage is the complete division of the egg, producing blastomeres of approximately equal size.

    • Unequal holoblastic cleavage produces blastomeres of unequal size due to the presence of a large yolk mass.

    • Meroblastic cleavage is incomplete division due to the presence of yolk and results in the formation of a discoidal morula.

    • Superficial meroblastic cleavage produces a layer of cells around a central mass of yolk.

    • The morula is a solid collection of cells that undergoes compaction, resulting in surface blastomeres becoming flattened and forming tight junctions.

    • The morula stage ends with the formation of a blastocyst or blastula, which is a hollow structure with a central cavity.

    • Mammals undergo regulative development, meaning that cells in early stages can lead to complete individuals when separated or fused.

    • Cytoplasmic determinants are components in the egg or zygote's cytoplasm that affect cell fate decisions through gene activities in specific cells.

    • Induction refers to the process of one embryonic region influencing another through secreted substances, causing cellular differentiation and tissue development.

    • Responding tissues can become inducing tissues, leading to a cascade of embryonic inductions that shape the body plan.

    • The dorsal blastopore lip in amphibian embryos is an example of an organiser centre responsible for the formation of the notochord and neural tube.

    • Organizer centres are groups of cells with the ability to instruct adjacent cells into specific states, playing a crucial role in developmental biology.

    • Morphogenesis, the development of shape and the organization of functional groups of organs, is achieved through complex interactions of cells during pattern formation. This process defines the specific spatial organization of organs and tissues.

    • Numerous fundamental inductions are mediated by signalling factors, such as those in the Fgf, Wnt, Tgf, and Hh families.

    • Induction involves a substance secreted by one group of cells altering the development of another group, often leading to instructive changes in cellular commitments.

    • Target cells only respond to induction signals when they express suitable receptors, which can vary in response to developmental time.

    • Organizer activity is often associated with structures like the primitive node in birds and mammals.

    • Morphogenesis, the development of shape and organization of tissues and organs, is a complex process involving pattern formation that drives the spatial arrangement of tissues and organs into a defined body plan.

    • During pattern formation in embryonic development, cells need to know their relative positions within the body plan.

    • Morphogens are intercellular molecular signals that provide positional information to target cells.

    • Morphogens act according to concentration gradients, with high concentrations near the source and low concentrations farther away.

    • Depending on the concentration of morphogens, cells receive different threshold levels and develop different cell fates.

    • Morphogens are often involved in creating concentration gradients in developing systems, such as the formation of limbs.

    • Animals can be composed of two or more genetically distinct cell populations, forming chimaeras or mosaics.

    • Chimaeras can be produced from the exchange of cells and genetic material during development, resulting in individuals with different genotypes.

    • Chimaeras are distinguished from hybrids, which are composed of genetically identical cell populations.

    • Twin chimaeras can be produced when two zygotes do not undergo fusion but share genetic material.

    • Identical twins are formed when a single fertilized egg splits into two, resulting in two genetically identical individuals.

    • Conjoined identical twins occur when blastomeres only partially separate, resulting in physically connected twins.

    • Success of surgical separation of conjoined twins depends on the degree of union and the skill of the surgical team.

    • Monozygotic twins are also known as identical twins and are formed from a single fertilized egg that splits into two.

    • Conjoined twins, also known as Siamese twins, are monozygotic twins with varying degrees of physical connection.

    • Different types of union in conjoined twins are named based on the region of connection (e.g., craniopagus for head connection).

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    Description

    Learn about the morula and blastocyst stages, early post-fertilization developments where cells divide rapidly and organize into a solid mass, and a hollow, fluid-filled structure, respectively.

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