What is replication in biology

This means that the new DNA molecule will consist of two strands: one that is newly created and the other is the original strand. DNA carries the genetic information that codes for a particular protein. Thus, DNA molecules have to be replicated prior to cell division to ensure that the two cells after cell division will have the same genetic content. In the early stages of mitosis prophase and meiosis prophase I , DNA is replicated in preparation for the late stages where the cell divides to give rise to two cells containing copies of DNA.

Thus, after replication, the new DNA molecule will be checked through stringent proofreading and repair mechanisms. The point at which the strands separate is referred to as the replication fork replication fork is a Y-shaped region in a chromosome that serves as the growing site for dna replication.

To remain separated, single-stranded binding proteins will bind to these strands. The enzyme primase will then attach a primer a short fragment of RNA. In particular, adenine will pair with thymine while guanine with cytosine. DNA polymerases, though, can move in only one direction, i. Thus, one of the original DNA strands will allow the polymerase to move along the strand and add nucleotides continuously.

This strand is called the leading strand. The other strand, called the lagging strand , runs in the opposite direction. Thus, the polymerase in the lagging strand tends to create short fragments called Okazaki fragments that are later joined together by DNA ligase. As a result of their different orientations, the two strands are replicated differently: An illustration to show replication of the leading and lagging strands of DNA.

Related Content:. What is a genome? What is DNA? What is a cell? How helpful was this page? What's the main reason for your rating? Which of these best describes your occupation? A single study examines only a subset of units, treatments, outcomes, and settings. The study was conducted in a particular climate, at particular times of day, at a particular point in history, with a particular measurement method, using particular assessments, with a particular sample.

Rarely do researchers limit their inference to precisely those conditions. If they did, scientific claims would be historical claims because those precise conditions will never recur. If a claim is thought to reveal a regularity about the world, then it is inevitably generalizing to situations that have not yet been observed. The fundamental question is: of the innumerable variations in units, treatments, outcomes, and settings, which ones matter?

Time-of-day for data collection may be expected to be irrelevant for a claim about personality and parenting or critical for a claim about circadian rhythms and inhibition. When theories are too immature to make clear predictions, repetition of original procedures becomes very useful. Using the same procedures is an interim solution for not having clear theoretical specification of what is needed to produce evidence about a claim.

Replication is not about the procedures per se, but using similar procedures reduces uncertainty in the universe of possible units, treatments, outcomes, and settings that could be important for the claim. However, every generalizability test is not a replication. The generalizability space is large because of theoretical immaturity; there are many conditions in which the claim might be supported, but failures would not discredit the original claim. The generalizability space has shrunk because some tests identified boundary conditions gray tests , and the replicability space has increased because successful replications and generalizations colored tests have improved theoretical specification for when replicability is expected.

For underspecified theories, there is a larger space for which the claim may or may not be supported—the theory does not provide clear expectations.

These are generalizability tests. Testing replicability is a subset of testing generalizability. As theory specification improves moving from left panel to right panel , usually interactively with repeated testing, the generalizability and replicability space converge.

Failures-to-replicate or generalize shrink the space dotted circle shows original plausible space. Successful replications and generalizations expand the replicability space—i. Successful replication provides evidence of generalizability across the conditions that inevitably differ from the original study; unsuccessful replication indicates that the reliability of the finding may be more constrained than recognized previously. Repeatedly testing replicability and generalizability across units, treatments, outcomes, and settings facilitates improvement in theoretical specificity and future prediction.

Theoretical maturation is illustrated in Fig 2. A progressive research program the left path succeeds in replicating findings across conditions presumed to be irrelevant and also matures the theoretical account to more clearly distinguish conditions for which the phenomenon is expected to be observed or not observed. This is illustrated by a shrinking generalizability space in which the theory does not make clear predictions.

A degenerative research program the right path persistently fails to replicate the findings and progressively narrows the universe of conditions to which the claim could apply. This is illustrated by shrinking generalizability and replicability space because the theory must be constrained to ever narrowing conditions [ 12 ].

With progressive success left path theoretical expectations mature, clarifying when replicability is expected. Also, boundary conditions become clearer, reducing the potential generalizability space. A complete theoretical account eliminates generalizability space because the theoretical expectations are so clear and precise that all tests are replication tests. With repeated failures right path the generalizability and replicability space both shrink, eventually to a theory so weak that it makes no commitments to replicability.

This exposes an inevitable ambiguity in failures-to-replicate. Was the original evidence a false positive or the replication a false negative, or does the replication identify a boundary condition of the claim? We can never know for certain that earlier evidence was a false positive. But that does not mean that all claims are true, and science cannot be self-correcting. Accumulating failures-to-replicate could result in a much narrower but more precise set of circumstances in which evidence for the claim is replicable, or it may result in failure to ever establish conditions for replicability and relegate the claim to irrelevance.

The ambiguity between disconfirming an original claim or identifying a boundary condition also means that understanding whether or not a study is a replication can change due to accumulation of knowledge. The original study was performed with so-called winter frogs. The replication attempts performed with summer frogs failed because of seasonal sensitivity of the frog heart to the unrecognized acetylcholine, making the effects of vagal stimulation far more difficult to demonstrate.

With subsequent tests providing supporting evidence, the understanding of the claim improved. What had been perceived as replications were not anymore because new evidence demonstrated that they were not studying the same thing. The theoretical understanding evolved, and subsequent replications supported the revised claims.

That is not a problem, that is progress. This is a useful research activity for advancing understanding, but many studies with this label are not replications by our definition. That is, they are not designed such that a failure to replicate would revise confidence in the original claim. Failures are interpreted, at most, as identifying boundary conditions. A self-assessment of whether one is testing replicability or generalizability is answering—would an outcome inconsistent with prior findings cause me to lose confidence in the theoretical claims?

If no, then it is a generalizability test. Designing a replication with a different methodology requires understanding of the theory and methods so that any outcome is considered diagnostic evidence about the prior claim. In fact, conducting a replication of a prior claim with a different methodology can be considered a milestone for theoretical and methodological maturity.

Replication is characterized as the boring, rote, clean-up work of science. This misperception makes funders reluctant to fund it, journals reluctant to publish it, and institutions reluctant to reward it.

The disincentives for replication are a likely contributor to existing challenges of credibility and replicability of published claims [ 14 ]. Single studies, whether they pursue novel ends or confront existing expectations, never definitively confirm or disconfirm theories. Theories make predictions; replications test those predictions.

Outcomes from replications are fodder for refining, altering, or extending theory to generate new predictions.