27.

(a) Give any four reasons for Mendel’s success.

(b) Briefly describe the technique employed in DNA fingerprinting.

(c) Give any two features of Genetic Code.

(a) Four reasons for Mendel's success:

1. Pea plant was easy to grow and interbreed and had a short life cycle so that several generations could be produced within a short period.

2 The flowers are bisexual containing both male and female parts. They are self-fertilising in nature. Because of easy self-fertilization, it is easy to get pure lines for several generations.

3. The pea plants had a number of contrasting characters. 

4. It was easy to hybridise because pollen from one plant could be introduced into the stigma of another plant by removing anthers.

(b) DNA fingerprinting involves a number of important steps in order to fully complete and develop and DNA fingerprint.

1. The process of DNA fingerprinting starts with isolating DNA from any part of the body such as blood, hair roots, teeth, bones, etc.

2. Polymerase chain reaction (PCR) is the next step in the process. In many situations, there is only a small amount of DNA available for DNA fingerprinting. PCR is used to amplify the small amount of DNA. It involves three steps Denaturation, annealing and extension.

3. After the DNA is isolated and more copies of the DNA have been made, the DNA wis treated with restriction enzymes (an enzymes that cuts DNA near specific recognition nucleotide sequences known as restriction sites). This is done to produce different sized fragments which are known as restriction fragment length polymorphisms.

4. These fragments can then be observed doing an experiment called gel electrophoresis which separates DNA based on fragment sizes.
Gel electrophoresis is the next step in this process of DNA fingerprinting. During gel electrophoresis, an electrical current is applied to a gel mixture, which includes the samples of the DNA. The electric current causes the DNA strands to move through the gel. This separates the molecules of different sizes. The fragments of separated DNA are sieved out of the gel using a nylon membrane (treated with chemicals that allow for it to break the hydrogen bonds of DNA so there are sing strands). The DNA (single stranded) is cross-linked against the nylon using heat or a UV light. The probe shows up on photographic film because the strands of DNA decay and give off light. In the end, it leaves dark spots on the film which are also known as the DNA bands of a person. What makes up the fingerprint are the unique patterns of bands. The pattern of bands are different because we are all different and unique (other than identical twins).

5. Once the filter is exposed to the x-ray film, the radioactive DNA sequences are shown and can be seen with the naked eye. This creates a banding pattern or what we know as DNA fingerprints. This technique is called southern blotting.

(c) Two features of the genetic code.

i. It is triplet and universal. The genetic code is called a universal code because all known organisms use the same four nucleotide bases; organism differ according to the arrangement of the nucleotide bases. The four nucleotide bases are adenosine, thymidine, cytidine and guanosine.
ii. Degenerative -The genetic code is degenerate because there are many instances in which different codons specify the same amino acid.