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

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (an insect of the Order (biology), 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", "pomace fly" ...

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

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 (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

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

motor neurons A motor neuron (or motoneuron), also known as 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 ...

which innervate

muscles Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

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 Aggression is behavior aimed at opposing or attacking something or someone. Though often done with the intent to cause harm, some might channel it into creative and practical outlets. It may occur either reactively or without provocation. In h ...

Function

Male Male (Planet symbols, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or Egg cell, ovum, in the process of fertilisation. A male organism cannot sexual repro ...

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

ritual A ritual is a repeated, structured sequence of actions or behaviors that alters the internal or external state of an individual, group, or environment, regardless of conscious understanding, emotional context, or symbolic meaning. Traditionally ...

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

alleles An allele is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule. Alleles can differ at a single position through single nucleotide polymorphisms (SNP), but they can also have insertions and deletions ...

; ''fru'' is necessary for every step in the ritual. Some alleles prevent courting entirely, while others disrupt individual components. Notably, some

loss-of-function In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis ...

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 Alternative splicing, alternative RNA splicing, or differential splicing, is an alternative RNA splicing, splicing process during gene expression that allows a single gene to produce different splice variants. For example, some exons of a gene ma ...

. 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+) which stabilizes the fold. The term ''zinc finger'' was originally coined to describe the finger-like appearance of a ...

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 A slang is a vocabulary (words, phrases, and linguistic usages) of an informal register, common in everyday conversation but avoided in formal writing and speech. It also often refers to the language exclusively used by the members of pa ...

word for

homosexual Homosexuality is romantic attraction, sexual attraction, or sexual behavior between people of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" exc ...

. 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 fro ...

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

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

. 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