White (mutation)

Last updated
white
White-eyed Drosophila.jpg
A white-eyed Drosophila
Identifiers
Organism Drosophila melanogaster
Symbolw1
UniProt P10090
Other data
Chromosome X: 2.79 - 2.8 Mb

white, abbreviated w, was the first sex-linked mutation discovered, found in the fruit fly Drosophila melanogaster. In 1910 Thomas Hunt Morgan and Lilian Vaughan Morgan collected a single male white-eyed mutant from a population of Drosophila melanogaster fruit flies, which usually have dark brick red compound eyes. Upon crossing this male with wild-type female flies, they found that the offspring did not conform to the expectations of Mendelian inheritance. [1] The first generation (the F1) produced 1,237 red-eyed offspring and three white-eyed male flies. The second generation (the F2) produced 2,459 red-eyed females, 1,011 red-eyed males, and 782 white-eyed males. Further experimental crosses led them to the conclusion that this mutation was somehow physically connected to the "factor" that determined sex in Drosophila. This led to the discovery of sex linkage, in which the gene for a trait is found on a sex chromosome. Morgan named this trait white, now abbreviated w. [2] Flies possessing the white allele are frequently used to introduce high school and college students to genetics.

Contents

Experimental cross performed by Thomas Hunt Morgan, illustrating the X-linked inheritance of white in Drosophila. Sex-linked inheritance.svg
Experimental cross performed by Thomas Hunt Morgan, illustrating the X-linked inheritance of white in Drosophila.

Function

The protein coded by the white gene functions as an ATP-binding cassette (ABC) transporter. It carries the precursors of the red and brown eye color pigments, guanine and tryptophan, into the developing eyes during pupation. [4] White-eyed flies are not blind; instead they are easily temporarily blinded by bright light at certain frequencies because they lack the protection provided by the red and brown pigments. [5] The human version of white is ABCG1, and is involved in transporting lipids and cholesterol into cells.

Effects mutation

Drosophila melanogaster with the white eye mutation typically have shorter life spans than wildtype Drosophila. They also experience many neurological deficiencies in addition to eye defects. Some of the deficiencies that they experience includes difficulty in mobility, and a low stress tolerance. Drosophila melanogaster with the white eye mutation often experience an increased sensitivity to light and a decrease in visual acuity. They have significantly less in the number of synaptic vesicles of photoreceptors.

White eye mutants of Drosophila melanogaster experience a lower rate of reproduction than their wildtype counterparts because they experience a reduced rate of sexual arousal during daylight. [6] Ectopic expression of white+ induces male-male courtship in Drosophila. [7] White+ controls the copulation success in Drosophila melanogaster. [8]

Notes and references

  1. Morgan TH (July 1910). "Sex Limited Inheritance in Drosophila". Science. 32 (812): 120–2. doi:10.1126/science.32.812.120. PMID   17759620.
  2. As the field of genetics developed, names for genes were italicized, and for Drosophila the normal (wild type) allele was given a + modifier, for example w+. Names of commonly used mutations were shortened, and since white was the first named, it was shortened to a single letter.
  3. Morgan TH (1919). The physical basis of heredity. Philadelphia: J.B. Lippincott Company.
  4. Mackenzie SM, Brooker MR, Gill TR, Cox GB, Howells AJ, Ewart GD (July 1999). "Mutations in the white gene of Drosophila melanogaster affecting ABC transporters that determine eye colouration". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1419 (2): 173–85. doi:10.1016/S0005-2736(99)00064-4. PMID   10407069.
  5. Cosens D, Briscoe D (April 1972). "A switch phenomenon in the compound eye of the white-eyed mutant of Drosophila melanogaster". Journal of Insect Physiology. 18 (4): 627–632. doi:10.1016/0022-1910(72)90190-4.
  6. Ferreiro MJ, Pérez C, Marchesano M, Ruiz S, Caputi A, Aguilera P, Barrio R, Cantera R (2017). "Drosophila melanogaster White Mutant w1118 Undergo Retinal Degeneration". Frontiers in Neuroscience. 11: 732. doi:10.3389/fnins.2017.00732. PMC   5758589 . PMID   29354028.
  7. Zhang SD, Odenwald WF (June 1995). "Misexpression of the white (w) gene triggers male-male courtship in Drosophila". Proceedings of the National Academy of Sciences of the United States of America. 92 (12): 5525–9. doi:10.1073/pnas.92.12.5525. PMC   41728 . PMID   7777542.
  8. Xiao C, Qiu S, Robertson RM (August 2017). "The white gene controls copulation success in Drosophila melanogaster". Scientific Reports. 7 (1): 7712. doi:10.1038/s41598-017-08155-y. PMC   5550479 . PMID   28794482.

Related Research Articles

<i>Drosophila</i>

Drosophila is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit. They should not be confused with the Tephritidae, a related family, which are also called fruit flies ; tephritids feed primarily on unripe or ripe fruit, with many species being regarded as destructive agricultural pests, especially the Mediterranean fruit fly.

<i>Drosophila melanogaster</i> Species of fruit fly

Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting with Charles W. Woodworth's proposal of the use of this species as a model organism, D. melanogaster continues to be widely used for biological research in genetics, physiology, microbial pathogenesis, and life history evolution. As of 2017, six Nobel prizes had been awarded for research using Drosophila.

Equine coat color genetics

Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. Extension and agouti are particularly well-known genes with dramatic effects. Differences at the agouti gene determine whether a horse is bay or black, and a change to the extension gene can make a horse chestnut instead. Most domestic horses have a variant of the dun gene which saturates the coat with color so that they are bay, black, or chestnut instead of dun, grullo, or red dun. A mutation called cream is responsible for palomino, buckskin, and cremello horses. Pearl, champagne and silver dapple also lighten the coat, and sometimes the skin and eyes as well. Genes that affect the distribution of melanocytes create patterns of white such as in roan, pinto, leopard, white, and even white markings. Finally, the gray gene causes premature graying, slowly adding white hairs over the course of several years until the horse looks white. Some of these patterns have complex interactions.

Sex linkage Sex-specific patterns of inheritance and presentation when a gene mutation is present on a sex chromosome

Sex linkage describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, X-linked dominant and Y-linked. The inheritance and presentation of all three differ depending on the sex of both the parent and the child. This makes them characteristically different from autosomal dominance and recessiveness.

In genetics, complementation occurs when two strains of an organism with different homozygous recessive mutations that produce the same mutant phenotype have offspring that express the wild-type phenotype when mated or crossed. Complementation will ordinarily occur if the mutations are in different genes. Complementation may also occur if the two mutations are at different sites within the same gene, but this effect is usually weaker than that of intergenic complementation. In the case where the mutations are in different genes, each strain's genome supplies the wild-type allele to "complement" the mutated allele of the other strain's genome. Since the mutations are recessive, the offspring will display the wild-type phenotype. A complementation test can be used to test whether the mutations in two strains are in different genes. Complementation ordinarily will occur more weakly or not at all if the mutations are in the same gene. The convenience and essence of this test is that the mutations that produce a phenotype can be assigned to different genes without the exact knowledge of what the gene product is doing on a molecular level. The complementation test was developed by American geneticist Edward B. Lewis.

In genetics, a reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern. All parent organisms must be true breeding to properly carry out such an experiment. In one cross, a male expressing the trait of interest will be crossed with a female not expressing the trait. In the other, a female expressing the trait of interest will be crossed with a male not expressing the trait. It is the cross that could be made either way or independent of the sex of the parents. For example, suppose a biologist wished to identify whether a hypothetical allele Z, a variant of some gene A, is on the male or female sex chromosome. She might first cross a Z-trait female with an A-trait male and observe the offspring. Next, she would cross an A-trait female with a Z-trait male and observe the offspring. Via principles of dominant and recessive alleles, she could then make an inference as to which sex chromosome contains the gene Z, if either in fact did.

The bead theory is a disproved hypothesis that genes are arranged on the chromosome like beads on a necklace. This theory was first proposed by Thomas Hunt Morgan after discovering genes through his work with breeding red and white eyed fruit flies. According to this theory, the existence of a gene as a unit of inheritance is recognized through its mutant alleles. A mutant allele affects a single phenotypic character, maps to one chromosome locus, gives a mutant phenotype when paired and shows a Mendelian ratio when intercrossed. Several tenets of the bead theory are worth emphasizing :- 1. The gene is viewed as a fundamental unit of structure, indivisible by crossing over. Crossing over take place between genes but never within them. 2. The gene is viewed as the fundamental unit of change or mutation. It changes in toto from one allelic form into another; there are no smaller components within it that can change. 3. The gene is viewed as the fundamental unit of function. Parts of a gene, if they exist cannot function. Guido Pontecorvo continued to work under the basis of this theory until Seymour Benzer showed in the 1950s that the bead theory was not correct. He demonstrated that a gene can be defined as a unit of function. A gene can be subdivided into a linear array of sites that are mutable and that can be recombined. The smallest units of mutation and recombination are now known to be correlated with single nucleotide pairs.

The term transheterozygote is used in modern genetics periodicals in two different ways. In the first, the transheterozygote has one mutant (-) and one wildtype allele (+) at each of two different genes. In the second, the transheterozygote carries two different mutated alleles of the same gene. This second definition also applies to the term "heteroallelic combination".

Position-effect variegation (PEV) is a variegation caused by the silencing of a gene in some cells through its abnormal juxtaposition with heterochromatin via rearrangement or transposition. It is also associated with changes in chromatin conformation.

The fruitless gene (fru) is a Drosophila melanogaster gene that encodes several variants of a putative transcription factor protein. Normal fruitless function is required for proper development of several anatomical structures necessary for courtship, including motor neurons which innervate muscles 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.

Sexual conflict Term in evolutionary biology

Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females, due to the anatomical differences of that species.

Balancer chromosomes are special, modified chromosomes used for genetically screening a population of organisms to select for heterozygotes. Balancer chromosomes can be used as a genetic tool to prevent crossing over between homologous chromosomes during meiosis. Balancers are most often used in Drosophila melanogaster genetics to allow populations of flies carrying heterozygous mutations to be maintained without constantly screening for the mutations but can also be used in mice. Balancer chromosomes have three important properties: they suppress recombination with their homologs, carry dominant markers, and negatively affect reproductive fitness when carried homozygously.

Paralytic is a gene in the fruit fly, Drosophila melanogaster, which encodes a voltage gated sodium channel within D. melanogaster neurons. This gene is essential for locomotive activity in the fly. There are 9 different para alleles, composed of a minimum of 26 exons within over 78kb of genomic DNA. The para gene undergoes alternative splicing to produce subtypes of the channel protein. Flies with mutant forms of paralytic are used in fly models of seizures, since seizures can be easily induced in these flies.

Ronald J. Konopka (1947-2015) was an American geneticist who studied chronobiology. He made his most notable contribution to the field while working with Drosophila in the lab of Seymour Benzer at the California Institute of Technology. During this work, Konopka discovered the period (per) gene, which controls the period of circadian rhythms.

Interlocus sexual conflict is a type of sexual conflict that occurs through the interaction of a set of antagonistic alleles at two or more different loci, or the location of a gene on a chromosome, in males and females, resulting in the deviation of either or both sexes from the fitness optima for the traits. A co-evolutionary arms race is established between the sexes in which either sex evolves a set of antagonistic adaptations that is detrimental to the fitness of the other sex. The potential for reproductive success in one organism is strengthened while the fitness of the opposite sex is weakened. Interlocus sexual conflict can arise due to aspects of male–female interactions such as mating frequency, fertilization, relative parental effort, female remating behavior, and female reproductive rate.

A behaviour mutation is a genetic mutation that alters genes that control the way in which an organism behaves, causing their behavioural patterns to change.

<i>Cycle</i> (gene)

Cycle (cyc) is a gene in Drosophila melanogaster that encodes the CYCLE protein (CYC). The Cycle gene (cyc) is expressed in a variety of cell types in a circadian manner. It is involved in controlling both the sleep-wake cycle and circadian regulation of gene expression by promoting transcription in a negative feedback mechanism. The cyc gene is located on the left arm of chromosome 3 and codes for a transcription factor containing a basic helix-loop-helix (bHLH) domain and a PAS domain. The 2.17 kb cyc gene is divided into 5 coding exons totaling 1,625 base pairs which code for 413 aminos acid residues. Currently 19 alleles are known for cyc. Orthologs performing the same function in other species include ARNTL and ARNTL2.

Jeffrey C. Hall

Jeffrey Connor Hall is an American geneticist and chronobiologist. Hall is Professor Emeritus of Biology at Brandeis University and currently resides in Cambridge, Maine.

Amita Sehgal is a molecular biologist and chronobiologist in the Department of Neuroscience at the Perelman School of Medicine at the University of Pennsylvania. Sehgal was involved in the discovery of Drosophila TIM and many other important components of the Drosophila clock mechanism. Sehgal also played a pivotal role in the development of Drosophila as a model for the study of sleep. Her research continues to be focused on understanding the genetic basis of sleep and also how circadian systems relate to other aspects of physiology.

<i>Drosophila</i> circadian rhythm

Drosophila circadian rhythm is a daily 24-hour cycle of rest and activity in the fruit flies of the genus Drosophila. The biological process was discovered and is best understood in the species Drosophila melanogaster. Other than normal sleep-wake activity, D. melanogaster has two unique daily behaviours, namely regular vibration during the process of hatching from the pupa, and during mating. Locomotor activity is maximum at dawn and dusk, while eclosion is at dawn.