
424 S.E.2d 440 (1993)
108 N.C. App. 401
STATE of North Carolina
v.
Charles Samuel BRUNO.
No. 915SC832.
Court of Appeals of North Carolina.
January 5, 1993.
*445 Atty. Gen., Lacy H. Thornburg, by Asst. Atty. Gen., Valerie B. Spalding, Raleigh, for the State.
Nora Henry Hargrove, Wilmington, for defendant-appellant.
EAGLES, Judge.

I
At the outset we note that the defendant raises twenty-two assignments of error. However, because the defendant has failed to bring forward assignments 1, 2, 5, 6, 8, 10, 11, 12, 14, 17, 18, 19, 21 and 22 in his brief, they are deemed abandoned. N.C.R.App.Pro. 28(b)(5).

II
By way of his third and fourth assignments defendant argues that the trial court committed reversible error by admitting DNA evidence. Specifically, defendant argues the evidence should have been excluded because: (1) the FBI's procedures are unreliable because they are in a state of flux and the results are not reproducible and (2) the trial court failed to resolve conflicts in the expert DNA testimony. We disagree.
In State v. Pennington, 327 N.C. 89, 393 S.E.2d 847 (1990), our Supreme Court determined that DNA evidence was sufficiently reliable to be admitted into evidence. In so determining, the Court
focused on the following indices of reliability: the expert's use of established techniques, the expert's professional background in the field, the use of visual aids before the jury so that the jury is not asked to "sacrifice its independence by accepting [the] scientific hypotheses on faith," and the independent research conducted by the expert.
Id. at 98, 393 S.E.2d at 853 (citation omitted). However, that admission was not without qualification.
The admissibility of any such evidence remains subject to attack. Issues pertaining to relevancy or prejudice may be raised. For example, expert testimony may be presented to impeach the particular procedures used in a specific test or the reliability of the results obtained. See, e.g., People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (1989). In addition, traditional challenges to the admissibility of evidence such as the contamination of the sample or chain of custody questions may be presented. These issues relate to the weight of the evidence. The evidence may be found to be so tainted that it is totally unreliable and, therefore, must be excluded.

State v. Ford, 301 S.C. [485] at 490, 392 S.E.2d [781] at 784 (1990). See also State v. Schwartz, 447 N.W.2d 422, 428 (Minn. 1989)....
Id. at 101, 393 S.E.2d at 854. We read Pennington to hold that a trial court may decide as a matter of law that DNA evidence is inadmissible for any number of reasons including, but not limited to, unreliable procedures or results, contamination of the sample or chain of custody questions. However, where unfair prejudice is not clear and where there is merely conflicting expert testimony regarding interpretation of the DNA evidence or where two experts have reached differing results based on independent analyses of the DNA, the issue becomes one of credibility of the experts. In that situation the jury is obligated to determine what weight each expert's testimony should receive.
Here, the defendant first argues that the procedures used by the FBI were unreliable because they are in a state of flux. More specifically, defendant argues that "[a]lthough the underlying procedure may be reliable, ... the F.B.I.'s witness showed that the procedure was still changing." The State correctly points out in its brief that the "[d]efendant appears to have overlooked the commonly known fact that most or all scientific procedures are constantly being refined in an effort to improve man's knowledge. If this were not so, our knowledge of ourselves and our universe would be both minimal and static."
The critical question here is not whether the DNA procedures were changing, but *446 whether the changes that have been made by the FBI demonstrate that the earlier procedures, which were used in the instant case, were so unreliable that the trial court should have completely excluded the evidence. The defendant admits in his brief that both Dr. Kloos and Dr. Nelson testified that the underlying procedures were reliable. Moreover, Dr. Deadman, the FBI's expert, addressed the concerns of the defendant. Dr. Deadman testified that there had been no significant changes in the testing procedures and that he would interpret the case the same way now as he did when the original tests were conducted. Defendant's argument is without merit.
Defendant next argues the FBI's procedures were unreliable because "Dr. Peiper was unable to reproduce their match analysis." Where two experts have reached differing results based on independent analyses, the jury is left to weigh the evidence. This argument is also without merit.
Finally, under this assignment, the defendant argues that the trial court erred by concluding that the DNA evidence was reliable. Specifically, defendant argues that the trial court erred by failing to resolve conflicts in expert testimony regarding interpretation of the fourth probe. Once again, this was an issue properly left to the jury. Accordingly, this argument is overruled.

III
By way of his seventh assignment of error defendant argues that the trial court erred by allowing both Dr. Deadman and Dr. Kloos to testify that the combined results of the several probes resulted in a stronger and more significant association than any one of the probes taken individually. However, the defendant failed to object when Dr. Nelson subsequently testified giving substantially the same testimony. "It is well settled that where evidence is admitted over objection, and the same evidence is later admitted without objection, the benefit of the objection is lost." State v. Beasley, 104 N.C.App. 529, 532, 410 S.E.2d 236, 238 (1991) (citing State v. Whitley, 311 N.C. 656, 319 S.E.2d 584 (1984)). This assignment is overruled.

IV
Defendant argues in his sixteenth assignment of error that the trial court erred by excising portions of Dr. Peiper's deposition testimony. We disagree.
Defendant first argues that the trial court erred by excising Dr. Peiper's testimony regarding the case of People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (1989). Defendant contends that Dr. Peiper should have been allowed to testify about the facts and name of the specific case to illustrate to the jury that DNA "tests are not infallible." According to defendant, if the jury heard a specific case name, "the idea of scientific fallibility [would] become[] real."
Assuming arguendo that the trial court committed error by excising the testimony, any error committed was harmless. Dr. Peiper was allowed to testify that there have been cases where false positives incriminate innocent suspects by mistake. Moreover, Dr. Peiper was allowed to testify that he was aware that the FBI had admitted making errors in two specific cases, Iowa v. Smith and New Mexico v. Anderson. This argument is overruled.
Defendant next argues that the trial court erred by excluding Dr. Peiper's testimony concerning the shortcomings of the FBI's data base. At trial the defendant made a motion in limine to prevent State witnesses "from making any reference to any numerical figure in connection with the DNA testing ... [because] the [FBI's] data base for attaching a numerical probability figure is inadequate and insufficient." The trial court allowed the defendant's motion in limine. The defendant now argues that because the trial court allowed the State's experts to testify that matches of multiple probes are more significant than a match of an individual probe, the trial court violated its own ruling and forced the defendant to choose between opening the door to statistical evidence of a match by impeaching the FBI's data base and "try[ing] to cut his losses by not allowing invalid and misleading *447 number crunching to be introduced." We have already determined that defendant here failed to properly preserve for our review the issue of whether the testimony regarding the significance of multiple matches was proper. Accordingly, we do not address that issue again. Furthermore, we note that it was the defendant who sought to exclude statistical evidence of a match because the FBI's data base was allegedly inadequate. He cannot now complain that his own expert was not allowed to testify to impeach the very data base evidence that he successfully asked be excluded. "A defendant is not prejudiced by the granting of relief which he has sought or by error resulting from his own conduct." G.S. 15A-1443(c); e.g. State v. Patterson, 332 N.C. 409, 420 S.E.2d 98 (1992). Accordingly, this assignment is overruled.

V
In his ninth assignment of error, the defendant argues that the trial court erred by allowing Dr. Deadman to testify that the fourth probe was inconclusive because the probative value of that evidence was outweighed by its prejudicial effect. We disagree.
During direct examination, Dr. Deadman testified that his examination of the fourth probe revealed that the bottom bands of the probe were a match. The upper bands, however, were inconclusive due to DNA degradation. In fact, Dr. Deadman testified that the upper four bands were essentially invisible. Dr. Deadman also testified that there was "streaking from the position of the defendant's upper band ... being consistent with degraded DNA." Dr. Deadman, over objection, explained the streaking as follows:
In order for an exposed area to develope [sic] in a piece of x-ray film the probe has to bind to something. The probe is only going to bind to particular pieces that have the sequence that it recognizes.
The probe is, in fact, binding to something in this upper region. If there were no bands above this lower band the probe would not be expected to bind to any great extent at that point and so the streaking from, from this upper point on down is consistent with something being there even though a distinct band cannot be seen.
Defendant argues that he was unfairly prejudiced by this testimony because Dr. Deadman was allowed to testify that there were matching bands when in fact there simply was no evidence to support his testimony. We disagree with defendant's interpretation of Dr. Deadman's testimony. Dr. Deadman did not testify that the streaking indicated there was a match among the upper bands of the fourth probe. Rather, his testimony merely explained to the jury why streaks appeared on the x-ray. Moreover, Dr. Deadman specifically testified that the upper bands were inconclusive. This assignment is overruled.

VI
By his thirteenth assignment defendant argues that the trial court committed reversible error by limiting the cross-examination of Dr. Kloos. At trial the following exchange occurred:
Q. You heard Dr. Deadman testify that even using computers and television cameras that the bands cannot be measured exactly?
A. Correct.
Q. So this is not an exact science by any means?
A. I look at the whole area of biology as perhaps a little less exact than physics, for example, if that's what you are using. I am surmising you may be using it as a standard for an exact science if there is such a beast.
Q. Do you think it is too much to demand with someone's liberty is at stake that the test be
MS. HOLT: Objection.
COURT: That objection is sustained.
A: I think
MS. HOLT: You don't need to answer.
COURT: Wait for the next question.
Defendant argues that the trial court's ruling effectively prevented him from properly developing "[t]he concept of scientific *448 error in a forensic setting and its consequences...." We disagree.
First, it should be noted that Dr. Kloos earlier testified that DNA is not yet automated and, therefore, is only as good as the people performing the tests. Second, the testimony which the defendant sought to elicit from Dr. Kloos is irrelevant here. Regardless of what standard Dr. Kloos feels should be applied, our Supreme Court has already adopted a standard to determine when a "scientific test" may be used to deprive someone of their liberty. E.g., State v. Bullard, 312 N.C. 129, 322 S.E.2d 370 (1984). This argument is wholly without merit.

VII
Defendant next argues, in his fifteenth assignment of error, that the trial court erred by denying his motion to dismiss the charge of second degree rape because there was no evidence of vaginal penetration. We disagree.
In ruling on a motion to dismiss for insufficient evidence the trial court must consider the evidence in the light most favorable to the state, which is entitled to every reasonable inference which can be drawn from that evidence. State v. Bell, 311 N.C. 131, 138, 316 S.E.2d 611, 615 (1984). There must, however, be substantial evidence of each essential element of the offense charged, together with evidence that the defendant was the perpetrator of the offense. State v. Gardner, 311 N.C. 489, 510-11, 319 S.E.2d 591, 605 (1984).
State v. McNicholas, 322 N.C. 548, 556-57, 369 S.E.2d 569, 574 (1988).
In order for a charge of second degree rape to withstand a motion to dismiss, evidence of vaginal intercourse must be presented. G.S. 14-27.3 (1986) "The slightest penetration of the female sex organ by the male sex organ is sufficient to constitute vaginal intercourse within the meaning of the statute." McNicholas, 322 N.C. at 556, 369 S.E.2d at 574. "It is not necessary that the vagina be entered or that the hymen be ruptured; the entering of the vulva or labia is sufficient." State v. Murry, 277 N.C. 197, 202, 176 S.E.2d 738, 742 (1970).
Here, the victim testified that the defendant attempted to have sex with her but couldn't because in the defendant's words, she was "too tight." Dr. Spicer testified that when he examined her he discovered a bruise around the right upper part of the lips of the vaginal vault in the entrance to the vagina consistent with vaginal penetration. This testimony was clearly sufficient on the issue of penetration to withstand the defendant's motion to dismiss. This assignment is overruled.

VIII
Defendant finally argues in his third, fourth, and twentieth assignments that admission of DNA analysis in the forensic setting is premature and deprived the defendant of his right to due process and a fair trial. To support this assignment, the defendant points to a number of "issues" raised by literature in the field. However, the defendant also concedes that our Supreme Court has already decided that North Carolina's courts are generally open to the admission of DNA evidence. State v. Pennington, 327 N.C. 89, 393 S.E.2d 847 (1990). Of course, the reliability of DNA evidence may be questioned in any given case. Id. This assignment does not bring forward a specific objection to the admission of DNA evidence in this case, but rather challenges its general admissibility. We are bound by the holding in Pennington. Accordingly, this assignment is overruled.

IX
Finally, we note that we are not directly confronted with the troublesome issue of whether the FBI's data base is sufficiently broad to allow introduction of evidence concerning the statistical probability that a given defendant is the perpetrator of a charged offense. Accordingly, we do not address it here.
No error.
PARKER and ORR, JJ., concur.
