Biological techniques to analyse evidence
Blood Group Analysis
The next type of evidence analysis is biological analysis, one of the first ones examples of this type of analysis is Blood Group Analysis. As we know blood is composed mostly of plasma, the blood also contains other components such as platelets, leucocytes (white blood cells) and erythrocytes (red blood cells). With forensics its important to know how each of the blood groups are composed, and how they can be utilized in the categorization of suspects, where their blood or other trace of DNA was found at the scene.

Steps
Forensic scientists utilize a system called the ABO system in order to categorize blood into groups, this is based on the type of antigen present in the body. And at a crime scene where blood was dropped either by the victim or the perpetrator, a serological is able to collect samples, and then take them to the laboratory so the person the blood belongs to can be identified, using a blood group testing machine. With this blood group system it is also possible to identify such blood group an individuals parents belong to. It is important to mention though that parents blood types can differ from those of their children, although through the use of techniques such as DNA fingerprinting  it is possible to identify some specific attributes, which shared between the parents and their offspring.

It is important to mention that using Blood Group Analysis is more of a form of identification than proving guilt, as although finding out the blood type of an individual from a sample is quite valuable, this method is just not precise enough in order to convict an individual. However in combination other things such as trace evidence and biological evidence, and witness accounts it can provide a good case in proving the guilt of an individual.

Advantages:
Blood Group Technique is quite a useful tool for forensic scientists, as it can be used to help say identify victims of crimes, and most importantly it can help link suspects to specific crimes. This method is also quite easy to carry out, as it is now possible to have portable blood testing machines. Also with the use of newer automatic blood group texting machines, the process is less tine consuming.

Disadvantages:
Although Blood Group Analysis has many advantages it does have some disadvantages, like using Blood Group Analysis to on its own to identify people. Although it is a useful technique in eliminating people as being suspects, it's less useful in positively linking people to crimes, for example 37% of the American population has O+ blood type so it would be hard to identify people based on just this method alone.

How Blood Pattern Analysis is used in different crimes
Blood Pattern Analysis can be used in a range of different crimes, like its main use in say robberies, homicides and sexual crimes would be helping in identify the perpetrator of the crime based on blood groups, which would be figured out based on their blood sample found at the scene. Of course similarly it can also be used to identify victims.

References
http://www.exploreforensics.co.uk/blood-types.html
https://www.enotes.com/homework-help/what-limitation-using-abo-blood-groups-identify-149923

DNA Profiling
The next biological method of analysis is fingerprint analysis, which is basically the process which a certain DNA pattern, referred to as a profile is obtained from a person or from a sample of their body tissue. Since each person receives a unique combination of polymorphisms from our parents, which are portions of DNA which differ a lot to offer people, this things can be analyses in order to obtain a DNA profile

Steps:
DNA is located in nearly all cells of our bodies, and can also be found in our bodily fluids due to them co tai b epithelial cells. These DNA samples are collected from crime scenes by police and forensic scientists, but can also be collected straight from a person using a swab. Since DNA is contained inside or the nucleus of our cells, in order to reach it forensic experts add chemicals to the cells in order to break them open, so that the DNA can be extracted from inside as well as be isolated from other components of the cell. Since DNA is only available in small quantities to forensic scientists to analyse, the STR's at each genetic locks are duplicated with use of a polymerase chain reaction, so that enough DNA is available for a DNA profile to be made about the perpetrator. From here the size or the STR's present at each genet8c locus is figured out using a genetic analyser. Based on the size of of the STR's, the amount of times a nucleotide sequence is repeated in each STR can be calculated. A forensic scientist is able use this info to be able to figure out whether or not a bodily fluid sample is from a specific person.

Advantages
The main advantage of the method of analysis, is that it can aid law enforcers identifying suspects based on body tissue which was deposited at the crime scene, like blood in a homicide case. This method of analysis can also aid in identifying victims too, especially if their bodies are too decayed to be identified just via observation. This method can also be used to figure out the family of individuals.

Disadvantages
One of the main problems with DNA profiling is the fact that some countries have DNA banks, in some cases people who were only arrested and not convicted have been logged onto the system which is not right. Another issue is things like DNA banks can violate people's privacy, as say if there was a breach in security, then someone could easily gain access to someone's personal information. Another issue is in recent years there have been some instances of DNA being planted at crime scenes which has led to innocent people being convicted. Finally as with any method of analysis, it is prone to a small amount of human error, also the method is quite complicated and time consuming and requires fully trained personnel to carry out.

How DNA Profiling is used in different crimes
DNA Profiling can be used in a range of different scenarios, like it can be used in homicides, say if the perpetrator left a blood sample at the scene, the DNA of the sample could be analysed in order to help identify the perpetrator. Or in say rape similarly a sample of semen could be analysed to help figure out the perpetrators identity. Pretty much in a crime if he perpetrator left behind some trade of DNA, this can provide valuable information about their identity. Additionally as stated earlier in crimes involving murder, DNA Profiling can be used to figure out the identity of a victim.

References for DNA Profiling
http://www.afsp.org.uk/node/52
https://www.sciencelearn.org.nz/resources/1980-dna-profiling

Chemical techniques to analyse evidence