21.1 Genetic Equivalence and Differential Gene Expression in Development

• Differentiation is the process in which cells acquire specialized properties.

• Differential gene expression is when different cells use the same set of genes in different ways.

• The idea that all the different cells in an organism contain the same genes is known as genetic equivalence

• When a branch or stem is removed from a plant, cells in the cut region can de-differentiate and begin dividing to form a mass of undifferentiated cells.

• Clones are a genetically identical copy

• Epigenetic inheritance is any form of inheritance that is not based on nucleotide sequence differences in alleles

21.2 Cells Are Determined Before They Differentiate

• Commitment occurs when an embryonic animal cell becomes dedicated to follow a particular path of cell specialization.

• Once a cell has locked into becoming a particular type of cell, it is said to be determined.

• A master regulator is a gene product that can unleash a series of events that produce a specialized cell type, tissue, or body structure

• Master regulators are used in the development of both animals and plants.

• But in later stages of development and in the adult, some populations of undifferentiated cells are maintained that preserve potential to divide throughout the individual’ s life which are stem cells.

• Producing one daughter that stays a stem cell ensures that populations of stem cells are maintained which is known as self-renewal.

• These cells, called embryonic stem cells, can form any cell in the body, a property known as pluripotency.

• They eventually hit on a combination of four transcription factors that caused some of the differentiated adult cells to de-differentiate to an embryonic stem-cell-like state. The resulting cells were called induced pluripotent stem cells, or iPS cells

21.3 Shared Developmental Processes

• An individual develops as:

  • cells divide

  • signal what they are doing, and what type of cell they are becoming

  • begin to express certain genes rather than others

  • move, expand, or contract in specific directions

  • in the case of some cells, die

• Fate is the type of cell they will ultimately form.

• Cytoplasmic determinants are gene regulatory molecules that are present in the cytoplasm of a dividing cell.

• Induction works through external signals.With induction, a cell that receives the signal is prompted to follow a different pathway of development and it would without the signal.

• In a stage of development called gastrulation, cells in different parts of the mass rearrange themselves into three distinctive layers, which then give rise to the skin, gut, and other basic parts of the body.

• Programmed cell death is a highly regulated and essential aspect of plant and animal development that occurs as tissues and organs take shape

21.4 Establishing the Body Plan

• Biologists use the term pattern formation to describe the events that determine the spatial organization of cells in an embryo.

• If embryonic cells detect these different concentrations and use this information to determine their location, then this molecule is a morphogen.

• A larva (plural: larvae) is a juvenile form between the hatched embryo and the adult

• Mutations that alter gene expression in the mother but affect the phenotype of her offspring are called maternal effect mutations.

• Segments arise early in development and produce characteristic body structures such as wings, legs, and antennae.

• A genetic regulatory cascade is a set of regulatory genes that are linked in such a way that one initially activated gene turns on the expression of other regulatory genes, which in turn trigger the expression of yet more regulatory genes.

• Hox gene products are transcription factors that achieve their effects by activating the expression of effector genes that ultimately lead to the production of particular proteins that create differentiated cells.

• Every Hox gene contains a conserved DNA sequence called the homeobox that codes for the DNA-binding domain of a Rox-encoded transcription factor.

• Homologous means that they are similar because they are descended from genes in a common ancestor

• Tool-kit genes are conserved sets of genes that code for signal proteins, signal transduction pathway components, and transcription factors that direct related aspects of development in many different species.

21.5 Changes in Developmental Gene Expression Drive Evolutionary Change

• An emerging research field called evolutionary developmental biology, or evo-devo, focuses on understanding how changes in developmentally important genes have led to the evolution of new forms such as the flower, the leaf, and animal limbs.