The ''fruitless'' gene (''fru'') is a ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

that encodes several variants of a putative

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The f ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

. Normal ''fruitless'' function is required for proper development of several anatomical structures necessary for courtship, including

motor neurons A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly ...

which innervate

muscles Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of musc ...

needed for fly sexual behaviors. The gene does not have an obvious mammalian homolog, but appears to function in sex determination in species as distant as the mosquito ''Anopheles gambiae''. ''fruitless'' serves as an example of how a gene or a group of genes may regulate the development and/or function of neurons involved in innate behavior. Research on ''fruitless'' has received attention in the popular press, since it provokes discussion on genetics of human sexual orientation, and behaviors such as gender-specific aggression.

Function

Male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

flies with mutations in the ''fruitless'' gene display altered sexual behavior. Fruitfly courtship, which involves a complex male-initiated

ritual A ritual is a sequence of activities involving gestures, words, actions, or objects, performed according to a set sequence. Rituals may be prescribed by the traditions of a community, including a religious community. Rituals are characterized ...

, may be disrupted in many ways by mutated ''fru''

alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...

; ''fru'' is necessary for every step in the ritual. Some alleles prevent courting entirely, while others disrupt individual components. Notably, some loss-of-function alleles change or remove sexual preference. Although many genes are known to be involved in male courtship behavior, the ''fruitless'' gene has been considered noteworthy because it exhibits sex-specific alternative splicing. When females produce the male-spliced gene product, they behave as males. Males that do not produce the male-specific product do not court females and are infertile. In the brain, a subset (ca. 2,000) of neurons express ''fruitless'' and ''fruitless'' expression is sufficient to instruct sexually dimorphic connectivity. ''fruitless'' has at least four promoters, each encoding proteins containing both a BTB (Broad complex/tramtrack/bric-a-brac) domain and a

zinc finger A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold. It was originally coined to describe the finger-like appearance of a hypothesized struct ...

motif. Alternative splicing occurs at both the 5' and 3' ends, and there are several variants (other than the male- and female-specific splicing patterns). The fruitless gene locus also controls the expression of hundreds of other genes, any subset of which may actually regulate behavior.

Name

Early work refers to the gene as ''fruity'', an apparent pun on both the common name of ''D. melanogaster'', the ''fruit fly'', as well as a

slang Slang is vocabulary (words, phrases, and linguistic usages) of an informal register, common in spoken conversation but avoided in formal writing. It also sometimes refers to the language generally exclusive to the members of particular in-g ...

word for homosexual. As

social Social organisms, including human(s), live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchange is voluntary or not. Etymology The word "social" derives from ...

attitudes towards homosexuality changed, ''fruity'' came to be regarded as offensive, or at best, not

politically correct ''Political correctness'' (adjectivally: ''politically correct''; commonly abbreviated ''PC'') is a term used to describe language, policies, or measures that are intended to avoid offense or disadvantage to members of particular groups in socie ...

. Thus, the gene was re-dubbed ''fruitless'', alluding to the lack of offspring produced by flies with the mutation. However, despite the original name and a continuing history of misleading inferences by the popular media, fruitless mutants primarily show defects in male-female courtship, though certain mutants cause male-male or female-female courtship.

References

External links

Entrez Gene summary for ''fruitless''
{{DEFAULTSORT:Fruitless (Gene) fruitless Molecular neuroscience Mating Sexual orientation and science Mutated genes Behavioural genetics