Methods for extracting DNA from semen.

The extraction of DNA from semen has some similarities with other specimens (e.g. blood, saliva, oral mucosa, hair), but also some specific differences. Semen is rich in DNA, making it suitable for DNA identification, but its composition and structure require specific procedures and precautions during extraction. The following section describes the characteristics of DNA extraction from semen and how it differs from other specimens.

1. Semen composition and DNA extraction characteristics

Semen is a fluid containing sperm and is mainly composed of the following elements

Sperm (containing DNA): sperm in semen are the main source of DNA.The nucleus of the sperm contains the genetic information of the father, which is used for identification.
Prostatic fluid andother body fluids: semen also contains fluid secreted from the prostate gland and seminal vesicles, which do not contain DNA.

DNA extraction from sperm is more difficult than from other cells in several ways. This is because the sperm cell nucleus is protected by a very strong membrane, making it more difficult to extract DNA than in other cells.

2. The specific procedures for extracting DNA from semen

Sperm separation and destruction: sperm have a very hard nuclear membrane compared to normal somatic cells and require special treatment to destroy the nucleus and extract the DNA.This treatment usually involves the use of more powerful chemicals and proteinase K (enzyme) to destroy the sperm nucleus.This causes DNA to be released from the nucleus.
Nucleic acid extraction methods: once the sperm nuclei have been destroyed, the usual DNA extraction process takes place.The phenol-chloroform method or commercially available DNA extraction kits are used to purify DNA from the semen.

3. Differences from other specimens

There are some important differences between DNA extraction from semen and DNA extraction from other specimens (e.g. blood, saliva, oral mucosa).

(1) Sperm nuclear strength.

Spermatozoa: The nucleus of sperm is very strong and DNA extraction is more labour intensive than in normal somatic cells. In particular, the nuclear membrane is more strongly protected than in other cells, so enzymes such as proteinase K must be used to destroy the nucleus.
Other specimens (e.g. blood, saliva, oral mucosa): the cells in these specimens (e.g. white blood cells, mucosal cells) have weaker nuclei than sperm, so DNA can easily be extracted using common DNA extraction methods (e.g. commercial DNA extraction kits).

(2) Amount of DNA.

Semen: sperm contain abundant DNA and sufficient amounts of DNA can be extracted from relatively small samples. In particular, high quality DNA is often obtained from semen, as it contains a large number of sperm.
Saliva and oral mucosa: DNA in saliva and oral mucosa is extracted from somatic cells (mainly white blood cells and oral epithelial cells).As these cells are few in number compared to sperm, it can be difficult to extract as large a quantity of DNA as semen.

(3) Difficulty of DNA extraction.

Semen: due to the very solid sperm nucleus, DNA extraction is time-consuming and requires special processing.In particular, DNA extraction from old semen or semen exposed to the environment can be even more difficult.
Blood: blood contains large amounts of white blood cells from which DNA can be easily extracted.Blood is generally considered the best specimen for DNA extraction.

(4) Effect of mixtures.

Semen: semen may contain other body fluids and impurities.In particular, post-sexual intercourse samples may contain female body fluids and other substances.In this case, different DNA may be mixed and it is necessary to distinguish between sperm DNA and other DNA.
Other specimens: saliva and blood allow individual DNA to be extracted relatively easily, with little risk of DNA contamination.

4. Effects of storage conditions

Semen: DNA in semen tends to deteriorate over time and DNA can be damaged if not stored properly.In particular, high temperatures and humid environments accelerate DNA degradation, so storage in refrigerated or frozen conditions is recommended.
Blood and saliva: Blood and saliva also deteriorate over time, but if stored well, the DNA is often relatively stable.

Summary

Special processing is required when extracting DNA from semen, compared to other specimens (e.g. blood or saliva), because the sperm nucleus is very solid. Semen contains abundant DNA, so even small amounts of semen can be used for highly accurate DNA analysis, but the possible presence of mixtures and poor storage conditions can make DNA extraction difficult. The main difference compared to other specimens is that DNA extraction is more time-consuming, as enzymatic treatment to destroy the sperm nuclei and the use of chemicals are mandatory.

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