Forensic Biology

RFLP is a multi-step DNA analysis technique. Let's arrange the steps in logical order.
Step 1: Prepare the DNA. The process must start with the DNA itself.
C. Isolation and restriction digestion of the DNA: First, DNA is extracted from the sample. Then, restriction enzymes are used to cut the DNA into fragments of different sizes. (After this, the fragments are separated by size using gel electrophoresis, which is an implicit step).

Step 2: Transfer the DNA. The DNA fragments from the gel must be transferred to a more stable medium for analysis.
B. Blotting of digested DNA onto a membrane: The separated DNA fragments are transferred from the gel to a nylon membrane in a process called Southern blotting.

Step 3: Label the DNA. Specific fragments of interest must be identified.
A. Probing hybridization of separated DNA: A radioactive or fluorescent probe (a short, known DNA sequence) is added. It binds (hybridizes) to its complementary sequence among the DNA fragments on the membrane.

Step 4: Detect the Labeled DNA. The location of the bound probe must be made visible.
D. Visualization by autoradiography: If a radioactive probe was used, the membrane is placed against an X-ray film. The radioactivity exposes the film, creating a band pattern that reveals the location of the specific DNA fragments.
The correct sequence is C B A D.

Step 1: Define the key terms.
(1) Phenotype: The observable characteristics of an individual, such as hair color, eye color, or blood type (e.g., Type A, Type B). It is the physical expression of the genes.
(2) Genotype: The specific genetic makeup or set of alleles of an individual. For ABO blood groups, this would be the combination of alleles like IA, IB, or i (e.g., IAIA, IAi, IBIB, IBi, IAIB, ii). The genotype determines the phenotype. The question asks for the "genetic constitution," which is the definition of genotype.
(3) Multiple genes: Refers to traits controlled by more than one gene (polygenic inheritance), which is not the case for the basic ABO system (controlled by one gene with multiple alleles).
(4) Pseudo genes: Segments of DNA that are related to real genes but have lost their protein-coding ability.

Step 2: Conclude. The term for the underlying genetic constitution is the genotype.

The ABO blood groups are determined by three alleles: , , and . A child inherits one allele from each parent.
- Genotype for Type O is . - Genotype for Type A is or . - Genotype for Type B is or . - Genotype for Type AB is .
Step 1: Evaluate each option.
(1) Mother (O) has genotype . Father (O) has genotype . They can only pass on the allele to their child. Therefore, their child MUST have genotype and be blood type O. A child with blood group "A" is impossible. This statement is incorrect.
(2) Mother, Father, and Child all have "A". This is possible. For example, if both parents have genotype , they can have a child with genotype or (Type A).
(3) Mother (A) and Father (B). This is possible. If Mother is and Father is , they can have a child with genotype (Type AB).
(4) Mother (O) and Child (O), Father (B). This is possible. Mother ( ) gives an allele. For the child to be O ( ), they must also get an allele from the father. This is possible if the father has genotype .
Conclusion: The scenario in option (1) violates the laws of Mendelian inheritance.

Step 1: Identify the protein. Keratin is the primary structural fibrous protein that makes up hair, feathers, horns, claws, and hooves.

Step 2: Determine the secondary structure. In mammals, the keratin in hair is -keratin. The secondary structure of -keratin is the -helix. (Beta-sheets are characteristic of -keratins found in reptiles and birds).

Step 3: Identify the cross-linking. The strength and insolubility of hair keratin come from extensive cross-linking between the -helical protein chains. These cross-links are primarily disulfide bonds, formed between cysteine amino acid residues.

Step 4: Evaluate the options. Option (1) correctly states both key features: an alpha-helix structure and cross-linking by disulfide bonds. The other options are incorrect regarding either the structure or the cross-linking.

The diatom test is used to confirm death by drowning.
Step 1: Understand the mechanism. When a person drowns, they inhale water. If they are alive, their heart is still beating. The inhaled water, containing microscopic algae called diatoms, enters the lungs.

Step 2: Diatom circulation. From the lungs, the diatoms pass through the damaged alveolar-capillary walls into the bloodstream. The circulatory system then distributes them throughout the body.

Step 3: Deposition. The diatoms are filtered out and deposited in various organs, particularly the bone marrow, which is well-protected from contamination. The femur (thigh bone) is a large bone with abundant marrow, making it an ideal sample site.

Step 4: Analyze other options. Nails and hair are external and can be easily contaminated by the water the body is found in. Fingerprints are skin patterns and not a site for diatom deposition. Therefore, the presence of diatoms deep inside the femur marrow is strong evidence of ante-mortem drowning.