Drosophila hybrid sterility

Last updated

The concept of a biological species as a group of organisms capable of interbreeding to produce viable offspring dates back to at least the 18th century, although it is often associated today with Ernst Mayr. Species of the fruit-fly Drosophila are one of the most commonly used organisms in evolutionary research, and have been used to test many theories related to the evolution of species. The genus Drosophila comprises numerous species that have varying degrees of premating and postmating isolation (including hybrid sterility) between them. These species are useful for testing hypotheses of the reproductive mechanisms underlying speciation.

In biology, a species ( ) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.

Ernst Mayr German-American evolutionary biologist

Ernst Walter Mayr was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, philosopher of biology, and historian of science. His work contributed to the conceptual revolution that led to the modern evolutionary synthesis of Mendelian genetics, systematics, and Darwinian evolution, and to the development of the biological species concept.

<i>Drosophila</i> genus of insects

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. One species of Drosophila in particular, D. melanogaster, has been heavily used in research in genetics and is a common model organism in developmental biology. The terms "fruit fly" and "Drosophila" are often used synonymously with D. melanogaster in modern biological literature. The entire genus, however, contains more than 1,500 species and is very diverse in appearance, behavior, and breeding habitat.

Contents

Historical background

Working in the early 20th century T.H. Morgan, was the first to use Drosophila to explore heredity. Primarily on the basis of work with D. melanogaster , Morgan and his colleagues C.B. Bridges, A.H. Sturtevant, and H.J. Mueller developed a chromosome theory of heredity, for which Morgan was awarded a Nobel Prize in 1933. Their experiments consisted of cross-breeding Drosophila mutants and documenting offspring. Another highly regarded figure in Drosophila research was Theodosius Dobzhansky, who invented the use of genetic markers and used them to study hybrid sterility between Drosophila pseudoobscura and Drosophila persimilis (Futuyma 1997). This experimental method has been used for many years.

<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, eight Nobel prizes had been awarded for research using Drosophila.

Hybrid (biology) offspring of cross-species reproduction

In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents, but can show hybrid vigour, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are.

Sterility is the physiological inability to effect sexual reproduction in a living thing, members of whose kind have been produced sexually. Sterility has a wide range of causes. It may be an inherited trait, as in the mule; or it may be acquired from the environment, for example through physical injury or disease, or by exposure to radiation.

Gender determination in Drosophila

The genome of D. melanogaster, has been sequenced and studied in fine detail. It is now known that Drosophila has 6 chromosomes—an X/Y pair and four autosomal chromosomes. The genome comprises about 139.5 million base pairs. There are about 15,000 genes.

Genome entirety of an organisms hereditary information; genome of organism (encoded by the genomic DNA) is the (biological) information of heredity which is passed from one generation of organism to the next; is transcribed to produce various RNAs

In the fields of molecular biology and genetics, a genome is the genetic material of an organism. It consists of DNA. The genome includes both the genes and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA. The study of the genome is called genomics.

Gender is determined in Drosophila not by the presence or absence of the Y chromosome as in mammals, but by the ratio of X chromosomes to autosomes.

Experimentation

In the off-spring of crosses between Drosophila simulans and its island derivative Drosophila mauritiana, female hybrids are fertile but male hybrids are sterile. Recent studies have shown that a critical gene for gender determination in Drosophila known as the sex-lethal gene is highly misregulated in D. melanogaster and D. simulans hybrids, compared with the degree of misregulation of non-sex biased genes studied. The sex-lethal gene is often abnormally expressed in male hybrids from D. melanogaster mothers as a result of re-localization of the male-specific complex to the X chromosome, which contributes to the male sterility. Abnormalities in sperm array were found in very few individuals during their larval stage, meaning that disruptions in spermatogenesis most likely occur during later stages in life. [ citation needed ]

Spermatogenesis The process of formation of spermatozoa giant , including spermatocytogenesis and spermiogenesis.

Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into spermatocytes. The primary spermatocyte divides meiotically into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa(sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells.

Experiments involving crosses between D. pseudoananassae and D. bipectinata, D. pseudoananassae and D. parabipectinata, and D. pseudoananassae and D. malerkotliana have further shown that the Y chromosome has a role in hybrid male sterility. The possible interactions of Y chromosome are X-Y, Y-autosome and Y-cytoplasm (Paras 2006). The sterile males carry a set of conspecific autosomes to the Y chromosome, which results in fertility because of the Y-dominant autosome interactions. Therefore, Y-autosome interactions are ruled out in this type of hybrid sterility.

Since cytoplasmic factors can be compatible between these species (Reference needed), such factors are also dismissed as the cause of sterility.

However, in Drosophila paulistorum there is information suggesting that if Y chromosome and cytoplasm are from different parents, the male is usually sterile. (Perez-Salas & Ehrman 1971) X-Y interactions are the most likely cause of sterility in male hybrids. It has been shown that interbreeding organisms that have more genetic compatibilities have less disruption of spermatogenesis and normal sized testes, while species who are less genetically compatible have a higher disruption in spermatogenesis and generally have atrophied testes. (Reference needed)

Another possible cause of sterility among species in which presence or absence of one or the other sex chromosome determines gender, is if one sex chromosome of one species has recessive alleles interacting with autosomal alleles of the mating species. This could cause the heterogametic sex chromosome in the hybrid to be inviable or sterile, but homogametic sex chromosome will be fertile (Futuyma 1997). Consequently, in species where presence or absence of a Y chromosome determines gender, for instance, individuals carrying XY chromosomes (males) will be sterile and those carrying XX (females) will be fertile. This is closely related to Haldane's rule.

Haldanes rule

Haldane's rule is an observation about the early stage of speciation, formulated in 1922 by the British evolutionary biologist J.B.S. Haldane, that states that if in a species hybrid only one sex is inviable or sterile, that sex is more likely to be the heterogametic sex. The heterogametic sex is the one with two different sex chromosomes; in therian mammals, for example, this is the male.

It has also been shown that microbial infections of invertebrates can cause modification of the gender and fertility of host's off-spring. For instance, infections of nematodes or of arthropods, including Drosophila, species of the rickettsial bacteria Wolbachia can produce a male-specific sterility, which is congenital by means of transmission through the female line.

Controversy

Experiments have led scientists to believe that many observations recorded in laboratories neglect existing polymorphism factors in hybrid sterility due to crossing parents from non-isofemale lines, as well as possibly underestimating actual degrees of sterility caused by inaccurate measures of motility. (Reference needed) Failure to account for potential polymorphism could lead to misinterpretation of the scale on which hybrid sterility occurs.

Related Research Articles

Chromosome DNA molecule containing genetic material of a cell

A chromosome is a deoxyribonucleic acid (DNA) molecule with part or all of the genetic material (genome) of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle.

Selfish genetic elements are genetic segments that can enhance their own transmission at the expense of other genes in the genome, even if this has no positive or a net negative effect on organismal fitness. Genomes have traditionally been viewed as cohesive units, with genes acting together to improve the fitness of the organism. However, when genes have some control over their own transmission, the rules can change, and so just like all social groups, genomes are vulnerable to selfish behaviour by their parts.

Sex-determination system A biological system that determines the development of sexual characteristics in an organism

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. Occasionally, there are hermaphrodites in place of one or both sexes. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization.

Y chromosome The sex chromosome present in males of species in which the male is the heterogametic sex; generally, the sex chromosome that pairs with the X chromosome in the heterogametic sex. The Y chromosome is absent from the cells of females and present in on

The Y chromosome is one of two sex chromosomes (allosomes) in mammals, including humans, and many other animals. The other is the X chromosome. Y is the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers testis development. The DNA in the human Y chromosome is composed of about 59 million base pairs. The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest-evolving parts of the human genome. To date, over 200 Y-linked genes have been identified. All Y-linked genes are expressed and hemizygous except in the cases of aneuploidy such as XYY syndrome or XXYY syndrome.

Sex linkage

Sex linkage describes the patterns of inheritance and presentation when a mutated gene is present on a sex chromosome rather than a non-sex chromosome. They are characteristically different from the autosomal forms of dominance and recessiveness.

Michael Ashburner biologist and emeritus Professor in the Department of Genetics at University of Cambridge

Michael Ashburner is a biologist and Emeritus Professor in the Department of Genetics at University of Cambridge. He is also the former joint-head and co-founder of the European Bioinformatics Institute (EBI) of the European Molecular Biology Laboratory (EMBL) and a Fellow of Churchill College, Cambridge.

Intragenomic conflict refers to the evolutionary phenomenon where genes have phenotypic effects that promote their own transmission in detriment of the transmission of other genes that reside in the same genome. The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects cause their transmission to new organisms, and most genes achieve this by cooperating with other genes in the same genome to build an organism capable of reproducing and/or helping kin to reproduce. The assumption of the prevalence of intragenomic cooperation underlies the organism-centered concept of inclusive fitness. However, conflict among genes in the same genome may arise both in events related to reproduction and altruism.

<i>Drosophila simulans</i> species of insect

Drosophila simulans is a species of fly closely related to D. melanogaster, belonging to the same melanogaster species subgroup. Its closest relatives are D. mauritiana and D. sechellia.

Meiotic drive is a type of intragenomic conflict, whereby one or more loci within a genome will affect a manipulation of the meiotic process in such a way as to favor the transmission of one or more alleles over another, regardless of its phenotypic expression. More simply, meiotic drive is when one copy of a gene is passed on to offspring more than the expected 50% of the time. According to Buckler et al., "Meiotic drive is the subversion of meiosis so that particular genes are preferentially transmitted to the progeny. Meiotic drive generally causes the preferential segregation of small regions of the genome".

The Drosophila melanogaster species subgroup contains 9 species of flies, including the best known species Drosophila melanogaster and D. simulans. The subgroup belongs to the Drosophila melanogaster species group within the subgenus Sophophora.

The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.

A metafemale is a low viability Drosophila fruit fly with a female phenotype in which the ratio of X chromosomes to sets of autosomes (A) exceeds 1.0. For example: a fly with one X chromosome and two sets of autosomes is a normal male, a fly with two X chromosomes and two sets of autosomes is a normal female, and a fly with three X chromosomes and two sets of autosomes is a metafemale.

Heterogametic sex sex of a species in which the sex chromosomes are not the same; e.g. human males (with XY chromosomes); bird females (with ZW chromosomes)

Heterogametic sex refers to the sex of a species in which the sex chromosomes are not the same. For example, in humans, males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex, and females having two X sex chromosomes would be referred to as the homogametic sex.

Cytoplasmic male sterility is total or partial male sterility in plants as the result of specific nuclear and mitochondrial interactions. Male sterility is the failure of plants to produce functional anthers, pollen, or male gametes.

Sex determination in <i>Silene</i>

Silene are a flowering plant that evolved a dioecious reproductive system. This is made possible through heteromorphic sex chromosomes expressed as XY. Silene recently evolved sex chromosomes 5-10 million years ago and are widely used by geneticists and biologists to study the mechanisms of sex determination since they are one of only 39 species across 14 families of angiosperm that possess sex-determining genes. Silene are studied because of their ability to produce offspring with a plethora of reproductive systems. The common inference drawn from such studies is that the sex of the offspring is determined by the Y chromosome.

References

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.