Homeosis
Encyclopedia
Homeosis is the transformation of one body part into another, arising from mutation
in or misexpression of specific developmentally critical gene
s. It may be caused by mutations in Hox genes, found in animals, or others such as the MADS-box
family in plants. Homeosis is a characteristic that has helped insect
s become as successful and diverse as they are.
Homeotic mutations work by changing segment identity during development. For example, the Ultrabithorax
genotype
gives a phenotype
wherein metathoracic and first abdominal segments become mesothoracic segments. Another well-known example is Antennapedia
: a gain-of-function allele
causes legs to develop in the place of antennae
.
In botany
, Rolf Sattler
has revised the concept of homeosis (replacement) by his emphasis of partial homeosis in addition to complete homeosis, which is commonly accepted.
Homeotic mutants in angiosperms are thought to be rare in the wild: in the annual plant Clarkia
, (Onagraceae
), homeotic mutants are known where the petals are replaced by a second whorl of sepal like organs, originating via a mutation governed by a single recessive gene. The absence of lethal or deleterious consequences in floral mutants resulting in distinct morphological expressions has been a factor in the evolution of Clarkia, and perhaps also in many other plant groups.
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
in or misexpression of specific developmentally critical gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s. It may be caused by mutations in Hox genes, found in animals, or others such as the MADS-box
MADS-box
The MADS box is a conserved sequence motif found in genes which comprise the MADS-box gene family. The MADS box encodes the DNA-binding MADS domain. The MADS domain binds to DNA sequences of high similarity to the motif CC[A/T]6GG termed the CArG-box. MADS-domain proteins are generally...
family in plants. Homeosis is a characteristic that has helped insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s become as successful and diverse as they are.
Homeotic mutations work by changing segment identity during development. For example, the Ultrabithorax
Ultrabithorax
Ultrabithorax or Ubx is a member of the homeobox gene family. Homeobox proteins function as transcription factors. In Drosophila melanogaster it is expressed in the third thoracic and first abdominal segments and represses wing formation. The Ubx gene regulates the decisions regarding the...
genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
gives a phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
wherein metathoracic and first abdominal segments become mesothoracic segments. Another well-known example is Antennapedia
Antennapedia
Antennapedia is a HOM-C gene first discovered in Drosophila which controls the formation of legs during development. Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae...
: a gain-of-function allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
causes legs to develop in the place of antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
.
In botany
Plant morphology
Plant morphology or phytomorphology is the study of the physical form and external structure of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level...
, Rolf Sattler
Rolf Sattler
Rolf Sattler, Ph.D., D.Sc. , F.L.S., F.R.S.C., is a Canadian plant morphologist, biologist, philosopher, and educator. He is considered one of the most significant contributors to the field of plant morphology. His contributions are not only empirical but involved also a revision of the most...
has revised the concept of homeosis (replacement) by his emphasis of partial homeosis in addition to complete homeosis, which is commonly accepted.
Homeotic mutants in angiosperms are thought to be rare in the wild: in the annual plant Clarkia
Clarkia
Clarkia is a genus within the flowering plant family Onagraceae. Over 40 species are currently classified in Clarkia; almost all are native to western North America, though one species is native to South America....
, (Onagraceae
Onagraceae
Onagraceae, also known as the Willowherb family or Evening Primrose family, are a family of flowering plants. The family includes about 640-650 species of herbs, shrubs, and trees in 20-24 genera...
), homeotic mutants are known where the petals are replaced by a second whorl of sepal like organs, originating via a mutation governed by a single recessive gene. The absence of lethal or deleterious consequences in floral mutants resulting in distinct morphological expressions has been a factor in the evolution of Clarkia, and perhaps also in many other plant groups.