10. (a) (i) The DNA molecule is composed of two strands held together by paired bases - Leaving Cert Biology - Question 10 - 2007

The base that can link only to cytosine is guanine.

The type of bonding that occurs between members of a base pair is hydrogen bonding.

DNA profiling refers to the process of examining DNA to identify patterns or bands that can be used for comparison. It typically involves extracting DNA, cutting it into fragments, and analyzing those fragments based on size or pattern.

The stages involved in DNA profiling generally include:

1. Extraction: DNA is extracted from a sample, such as saliva or blood.
2. Amplification: The DNA is amplified using techniques like PCR (Polymerase Chain Reaction) to produce sufficient quantities for analysis.
3. Fragmentation: The DNA is cut into smaller fragments using restriction enzymes.
4. Separation: These fragments are separated, typically by size, through a process called gel electrophoresis.
5. Analysis: The resulting DNA bands are analyzed and compared to determine the identity or relationships among individuals.

Two applications of DNA profiling include:

1. Forensic Science: It is used in criminal investigations to match DNA found at crime scenes with potential suspects.
2. Medical Diagnostics: The technique can help in establishing paternity or identifying genetic disorders.

Genetic screening is the process of testing individuals for the presence of specific genes or genetic markers that may indicate a risk of developing certain diseases or conditions. This helps in early detection and management of genetic disorders.

The statement emphasizes that all somatic cells in an organism, including those from the liver, heart, pancreas, and muscle, contain the same amount of DNA because they originate from the same zygote. During mitosis, the chromosome number is maintained, ensuring that daughter cells have identical DNA content.

A gamete (sperm or egg cell) produced by the rat will contain a different amount of DNA, specifically half the amount, due to the process of meiosis which results in haploid cells.

To isolate DNA from plant tissue, follow these steps:

1. Chop the plant tissue into small pieces.
2. Add a solution containing salt and detergent to break down cell membranes and release DNA.
3. Warm the mixture to 50-60 degrees Celsius to denature proteins.
4. Cool the mixture and blend it gently to mix.
5. Filter the mixture to remove debris.
6. Precipitate the DNA by adding cold ethanol which causes the DNA to separate out of the solution.