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GENETIC DRIFT

Published in Zoology
Sunday, 11 June 2017 05:49
Genetic drift as one of the evolutionary force
 
The genetic architecture of small population changes irrespective of elective advantage or disadvantage. Analogously genes attain Hardy-Weinberg’s equilibrium in large populations only. The random changes in gene frequencies occurring by chance and not under the control of natural selection are called genetic drift. A series of steps and at each step the movement made is random, in directed which Is known as stochastic process.

The theory of genetic drift was developed by a geneticist SE WALL WRIGHT in 1930. It is also known as Sewall Wright effect or ‘scattering of variability’. It denotes that the random fluctuations in the gene frequencies In a small population from generation to generation.

In demes of limited sizes, random genetic drifts arise by chance. These cannot arise in large population. For example if we compare two populations of two extreme sizes - Population ‘A’ consisting of 5,000 breeding individuals and population ‘B’ of only 50, the gene pool of each contains equal number of Land I. If their gene frequencies are represented by p & q
 
pL= qI -0.5

In the next generation, the gene frequency is expected to deviate from the original 0. 5 by an amount of equal to the ‘standard error’
 
geneticdrift1
 
The standard error is determined as the sequence root of the product of original frequencies (p & q) divided by the number of genes available. This number of genes will be double the number of breeding organisms.
 
In small population B with organisms, the standard error would be J(o. 5 x 0.5 + 1oo) = 0.05. So in the next generation the gene frequencies will change to 0.45 and 0.55 either way. This amounts to 10% change in the gene frequency. Thus the standard error in a large population’s) + 10,000 = 0.0005) is negligible and it significantly high in a small population.

Effects of Genetic Drift on Gene frequency
 
In small populations or demes, the genetic drifts have the following, effects on the gene-frequency.

i) Homozygocity: In small populations, due to genetic drift gene frequencies continue to fluctuate until one of the allele lost and other fixed. This leads homozygosity in small populations. It means the genetic drift reduces genetic variability by eliminating one of the two alleles ‘either new or old one.
 
ii) Fixation of new mutations: Since genetic drift tend to eliminate one allele and fix the other one, irrespective of its dominance or recessiveness or advantageous or non advantageous nature. So a new mutation has 50% chances of either being lost or be fixed in small population.

iii) Genetic divergence: The demes become progressively genetically different. In each sub population, the genes fixed and lost will be different. Thus, In due course of time, (each deme gradually diversifies from the other sister demes) lead to the establishment of new species.
 
geneticdrift21
 
Genetic Drift and Evolution:
 
The role played by the genetic drifts actually in the evolution of organisms in nature is doubtful. A widely ranging broad base population is isolated into small sub groups - ‘DEMES’. The causes for isolation may be either on account of ecological or geographical discontinuities, home instinct. The size of these small demes is such that they appear to be affected by chance of events underlying genetic drift. The limited size of small breeding populations, the gene pool of their new generations may not be the same of the parental gene pools due to the action of genetic drift. The changed gene pools gradually lead to the formation of new species.

Founder Effect: Whenever a few organisms from large population encroaches a new or isolated geographical region, these form the “founders or ‘founder members’. The founders carry only a limited portion of the parental gene pool. The descendants of the founder i.e. the founder population or marginal isolates in a new area will tend to have ratios similar to the founders. The resemblance of the descendants of the founders is called founders effect’ or ‘founder principle’ (Maw).

The diffusion of genes into populations through migrations and interbreeding is known as Gene flow. The gene flow links all the demes of a population. It tends to counteract the loss of variability due to genetic drift in small population.
 
Rh gene (r) was introduced into the Chinese population by American immigrants. This Rh factor is associated with erythroblastosis fetalis or hemolytic disease in new born.

Principles of Genome Analysis and Genomics, 3rd Ed.

Published in Downloads
Sunday, 30 October 2016 20:52
Description: With the first draft of the human genome project in the public domain and full analyses of model genomes now available, the subject matter of 'Principles of Genome Analysis and Genomics' is even 'hotter' now than when the first two editions were published in 1995 and 1998. In the new edition of this very practical guide to the different techniques and theory behind genomes and genome analysis, Sandy Primrose and new author Richard Twyman provide a fresh look at this topic. In the light of recent exciting advancements in the field, the authors have completely revised and rewritten many parts of the new edition with the addition of five new chapters. Aimed at upper level students, it is essential that in this extremely fast moving topic area the text is up to date and relevant.
  • Completely revised new edition of an established textbook.
  • Features new chapters and examples from exciting new research in genomics, including the human genome project.
  • Excellent new co-author in Richard Twyman, also co-author of the new edition of hugely popular Principles of Gene Manipulation.
  • Accompanying web-page to help students deal with this difficult topic at www.blackwellpublishing.com/primrose

Zika Virus Infection Alters Human and Viral RNA

Published in News
Monday, 24 October 2016 17:14
Researchers at University of California San Diego School of Medicine have discovered that Zika virus infection leads to modifications of both viral and human genetic material. These modifications — chemical tags known as methyl groups — influence viral replication and the human immune response. The study is published October 20 by Cell Host & Microbe.
 
“I’m excited about this study because it teaches us something new about the human immune system,” said senior author Tariq Rana, PhD, professor of pediatrics at UC San Diego School of Medicine. “But these findings are also something researchers should keep in mind as they are designing new Zika virus vaccines and treatments that target the viral genome — some approaches won’t work unless they take methylation into account.”
 
In human cells, RNA is the genetic material that carries instructions from the DNA in a cell’s nucleus out to the cytoplasm, where molecular machinery uses those instructions to build proteins. Cells can chemically modify RNA to influence protein production. One of these modifications is the addition of methyl groups to adenosine, one of the building blocks that make up RNA. Known as N6-methyladenosine (m6A), this modification is common in humans and other organisms.
 
In contrast to humans, the entire genomes of some viruses, including Zika and HIV, are made up of RNA instead of DNA. These viruses hijack the host’s cellular machinery to translate its RNA to proteins. Rana and his team previously discovered that m6A plays an important role in HIV infection.
 
“After that, we decided to investigate m6A RNA in Zika virus as well, since we didn’t want to miss out on this important information the way we missed it for 30 years of HIV research,” Rana said.
 
When Zika virus infects a human cell, Rana’s team found, the cell modifies viral RNA with m6A as a means to get rid of the infection. RNA tagged with m6A is a beacon for human enzymes that come along and destabilize it. In addition, they found that this host response to Zika viral infection also induced specific m6A modifications on human RNA. These human RNA changes were not present in the absence of Zika virus.
 
To unravel the role of m6A in Zika virus infection of human cells growing in the laboratory, the researchers removed the human enzymes responsible for adding methyl groups to viral RNA. Without m6A, the viral RNA was more stable and viral replication increased, as compared to human cells with normal methylation enzymes. In contrast, silencing the human enzymes that remove methyl groups — increasing m6A methylation, in other words — decreased Zika virus production.
 
Next, Rana and team will investigate the role of RNA modifications in the viral life cycle, and how the human immune response is altered by various Zika virus strains. They are also developing small molecules to target specific RNA structures as a means to treat Zika virus infections.
 
Study co-authors include: Gianluigi Lichinchi, Yinga Wu, UC San Diego and Sanford Burnham Prebys Medical Discovery Institute; Boxuan Simen Zhao, Zhike Lu, Chuan He, University of Chicago and Howard Hughes Medical Institute; and Yue Qin, UC San Diego.
 
This research was funded, in part, by the National Institutes of Health (grants AI43198, AI125103, DA039562) and Howard Hughes Medical Institute.

Author: Heather Buschman, PhD

BRS Biochemistry, Molecular Biology, and Genetics 6th Ed.

Published in Downloads
Saturday, 17 September 2016 13:41
Description: BRS Biochemistry, Molecular Biology, and Genetics is an excellent aid for USMLE Step 1 preparation and for coursework in biochemistry, molecular biology, and genetics. Fully updated for its sixth edition, chapters are written in an outline format and include pedagogical features such as bolded key words, figures, tables, algorithms, and highlighted clinical correlates. USMLE-style questions and answers follow each chapter and a comprehensive exam appears at the end of the book.

Detection of Nucleic Acid Sequences of Malaria Parasites

Published in Genetics
Tuesday, 06 September 2016 21:15
Malaria parasites can be detected by identification of specific nucleic acid sequences in their DNA. Methods based on polymerase chain reaction (PCR) have been developed for identification of DNA of malaria parasite. Species diagnosis is also possible. PCR-based methods can detect very low levels of parasites in blood (< 5 parasites/μl of blood) with very high sensitivity and specificity.
 
Molecular methods can be useful in the diagnosis of malaria, in following response to treatment, in epidemiological surveys, and for screening of blood donors. They can also be used as a standard to judge other methods of malaria diagnosis. However, these methods cannot be routinely applied because of the high cost, need for special equipments and materials, and lengthy procedure (24 hours). Presently they can be used as a research tool in malaria control programs, and to carry out quality control checks on microscopic diagnosis.
 
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Bacterial Genetics

Published in Bacterial Genetics
Saturday, 23 April 2016 13:02
Bacterial genetics is the subfield of genetics devoted to the study of bacteria. Bacterial genetics are subtly different from eukaryotic genetics, however bacteria still serve as a good model for animal genetic studies. One of the major distinctions between bacterial and eukaryotic genetics stems from the bacteria's lack of membrane-bound organelles (this is true of all prokaryotes. While it is a fact that there are prokaryotic organelles, they are never bound by a lipid membrane, but by a shell of proteins), necessitating protein synthesis occur in the cytoplasm.
 
Like other organisms, bacteria also breed true and maintain their characteristics from generation to generation, yet at same time, exhibit variations in particular properties in a small proportion of their progeny. Though heritability and variations in bacteria had been noticed from the early days of bacteriology, it was not realised then that bacteria too obey the laws of genetics. Even the existence of a bacterial nucleus was a subject of controversy. The differences in morphology and other properties were attributed by Nageli in 1877, to bacterial pleomorphism, which postulated the existence of a single, a few species of bacteria, which possessed a protein capacity for a variation. With the development and application of precise methods of pure culture, it became apparent that different types of bacteria retained constant form and function through successive generations. This led to the concept of monomorphism.

Genetics

Published in Genetics
Saturday, 23 April 2016 12:54
Genetics is the study of genes, heredity, and genetic variation in living organisms. It is generally considered a field of biology, but it intersects frequently with many of the life sciences and is strongly linked with the study of information systems.
 
The father of genetics is Gregor Mendel, a late 19th-century scientist and Augustinian friar. Mendel studied 'trait inheritance', patterns in the way traits were handed down from parents to offspring. He observed that organisms (pea plants) inherit traits by way of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred to as a gene.
 
Trait inheritance and molecular inheritance mechanisms of genes are still a primary principle of genetics in the 21st century, but modern genetics has expanded beyond inheritance to studying the function and behavior of genes. Gene structure and function, variation, and distribution are studied within the context of the cell, the organism (e.g. dominance) and within the context of a population. Genetics has given rise to a number of sub-fields including epigenetics and population genetics. Organisms studied within the broad field span the domain of life, including bacteria, plants, animals, and humans.
 
Genetic processes work in combination with an organism's environment and experiences to influence development and behavior, often referred to as nature versus nurture. The intra- or extra-cellular environment of a cell or organism may switch gene transcription on or off. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate. While the average height of the two corn stalks may be genetically determined to be equal, the one in the arid climate only grows to half the height of the one in the temperate climate, due to lack of water and nutrients in its environment.
 
History
The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. The modern science of genetics, seeking to understand this process, began with the work of Gregor Mendel in the mid-19th century.
 
Although the science of genetics began with the applied and theoretical work of Mendel, other theories of inheritance preceded his work. A popular theory during Mendel's time was the concept of blending inheritance: the idea that individuals inherit a smooth blend of traits from their parents. Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes rather than a continuous blend. Blending of traits in the progeny is now explained by the action of multiple genes with quantitative effects. Another theory that had some support at that time was the inheritance of acquired characteristics: the belief that individuals inherit traits strengthened by their parents. This theory (commonly associated with Jean-Baptiste Lamarck) is now known to be wrong—the experiences of individuals do not affect the genes they pass to their children, although evidence in the field of epigenetics has revived some aspects of Lamarck's theory. Other theories included the pangenesis of Charles Darwin (which had both acquired and inherited aspects) and Francis Galton's reformulation of pangenesis as both particulate and inherited.

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