Although scientists have known for more than a century that small populations of closely related plants or animals are likely to suffer from low reproductive success, the exact mechanism by which this “inbreeding depression” occurs is still the subject of debate.
The new study, in Conservation Biology, is the first to look at inbreeding depression as it relates to the expression of all of an organism’s genes – to see which are more or less active in inbred populations and what they do.
By mating male and female fruit flies that were genetically identical to one another, researchers at the University of Illinois were able to determine how much the flies’ genetic likeness reduced their reproductive success. They repeated the experiment in six lines of fruit flies that were identical to one another except for the composition of one of their chromosomes; only the genes of chromosome three differed between the lines.
The researchers also crossed the three highest inbred lines to one another, creating outbred lines that could be compared with the inbred ones.
Using oligonucleotide microarrays, which can measure the activity of all of an organism’s genes at once, the researchers were able to see which genes were more or less active (up-regulated or down-regulated) in the inbred versus the outbred lines.
The six inbred lines of fruit flies showed a lot of variation in the degree of inbreeding depression, from 24 to 79 percent when compared with non-inbred flies. The researchers also found that 567 genes in the high inbreeding depression lines were expressed at higher or lower levels than the same genes in the other inbred lines. Only 62 percent of these genes were located on chromosome three (the only chromosome that differed between the lines) indicating that variation in chromosome three had altered gene expression on the other chromosomes.
“These results suggest that a significant amount of inbreeding depression is due to a few key genes that affect the expression of other genes,” said animal biology professor and department head Ken Paige, who led the study.
Of particular note were identical changes in the expression of 46 genes in all three of the high inbreeding depression lines, Paige said, making them of interest for further study.
Genes associated with inbreeding depression could be grouped into three broad categories of function: those involved in metabolism, stress, and defense. This is a surprising finding, Paige said, “because we think of inbreeding as a random process.”
Many metabolic genes were up-regulated in the inbred flies, as were genes that fight pathogens such as bacteria or viruses. A third group of genes was down-regulated. They code for proteins that protect the body from reactive atoms and molecules that can damage cells.
These changes in gene expression are shunting energy away from reproduction and undermining some basic cellular functions, Paige said.
Inbreeding depression is thought to result from a deleterious pattern of inherited genes. In general, an organism with two parents has two versions of every gene – one maternal and one paternal. These different flavors of a gene are called alleles. If the maternal and paternal alleles differ, one of them usually dominates, conferring all of its qualities to the offspring. The other, silenced allele is called “recessive.”
Some alleles are detrimental to health. Most of these are recessive, meaning that they do not cause problems unless the organism inherits two copies of them – one from each parent. When the alleles differ, one (the dominant allele) often masks the deleterious effects of the other.
But the interaction of parental alleles in their offspring can be quite complex. Sometimes an allele causes a disease or disorder even if it is paired with a different allele. Sometimes several genes influence a single trait. And sometimes two different alleles can lead to a higher level of gene activity than occurs in either parent (this last phenomenon is called overdominance).
When closely related individuals mate, their offspring are likely to end up with identical alleles for many traits. Many potentially harmful recessive alleles are no longer masked by dominant alleles, so more genetic disorders arise. Similarly, offspring that inherit two identical alleles for some traits will also lose any advantages once conferred by overdominance.
Biologists have long wondered which of these mechanisms causes the reproductive failures seen in inbred populations. “It’s still being debated,” Paige said.
The new study found that about 75 percent of the reproductive declines seen in the inbred flies could be attributed to the loss of dominant alleles and the subsequent “unmasking” of deleterious alleles. More surprisingly, the data also indicated that 25 percent of the declines were due to the loss of overdominance.
“That means we have two mechanisms ongoing,” Paige said. “One does predominate, but the other may be important, too.”
The fact that a relatively large number of genes are affected by inbreeding is bad news for conservationists hoping to save small populations of plants or animals from extinction, Paige said.
It means that there is no easy fix to the problem of inbred populations. The best approach is to try to preserve and maintain genetic diversity in natural populations well before they begin their slide into an “extinction vortex,” he said.
Co-authors on the study included natural resources and environmental sciences graduate student Julien Ayroles, animal biology professor Kimberly Hughes, animal biology doctoral student Kevin Rowe, animal biology technician Melissa Reedy, animal biology postdoctoral researcher Jenny Drnevich, animal biology professor Carla Cáceres, and animal sciences professor Sandra Rodriguez-Zas, who is also an affiliate of the Institute for Genomic Biology.
Diana Yates | University of Illinois
First time-lapse footage of cell activity during limb regeneration
25.10.2016 | eLife
Phenotype at the push of a button
25.10.2016 | Institut für Pflanzenbiochemie
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
26.10.2016 | Power and Electrical Engineering
26.10.2016 | Awards Funding
26.10.2016 | Power and Electrical Engineering