Genetics

The question asks about the chromosomal aberration illustrated in the diagram, with multiple-choice options provided. The correct answer is 'Inversion'. Let's explore the reasoning behind this and understand why the other options are not correct.

1. Understanding Chromosomal Inversion:
   • An inversion occurs when a segment of a chromosome breaks off and reattaches in the reverse direction. This results in the genetic material being inverted within the chromosome.
   • This type of structural alteration does not involve a change in the amount of genetic material, but rather a reorganization.
2. Comparing with Other Types of Aberrations:
   • Deletion: This involves the removal of a chromosome segment, resulting in a loss of genetic material. It would not show inverted regions.
   • Duplication: This involves repeating a segment of a chromosome, resulting in an increase in genetic material. Unlike inversion, the orientation remains the same.
   • Translocation: This occurs when a segment of one chromosome is transferred to another, non-homologous chromosome. This involves two different chromosomes rather than a single chromosome, unlike inversion.
3. Conclusion:
   • The diagram, by illustrating a section of a chromosome with a reversed sequence, corresponds to an inversion.

i. Incomplete Dominance: A genetic phenomenon where neither allele is completely dominant, resulting in an intermediate phenotype in heterozygotes (e.g., pink flowers in Mirabilis jalapa from red and white parents).

ii. F2 Phenotypic Ratio:
Let red flower allele = R, white flower allele = r.
- Parents: Red (RR) × White (rr) → F1: Pink (Rr).
- F1 self-cross: Rr × Rr.

Punnett Square:

F2 Phenotypic Ratio: 1 Red : 2 Pink : 1 White

Answer: i. Intermediate phenotype in heterozygotes; ii. 1:2:1 (Red : Pink : White).

Answer: X has longer non-homologous regions and is metacentric/submetacentric; Y has shorter regions and is acrocentric.

Overview of Chromosomal Disorders: Chromosomal disorders are genetic conditions that arise from anomalies in chromosome number or structure, resulting in various developmental and health issues.
-Aneuploidy: An atypical number of chromosomes.
-Structural alterations such as deletion, duplication, or translocation of chromosomal segments.
Common Chromosomal Disorders:
1. Turner’s Syndrome (45, XO):
-Characterized by the loss of one X chromosome in females.
-Features include short stature, webbed neck, and poorly developed ovaries.
-Results in infertility, absence of secondary sexual traits, and possible cardiac issues.
2. Klinefelter’s Syndrome (47, XXY):
-Occurs in males due to an additional X chromosome.
-Presents with tall stature, sparse body hair, gynecomastia, and small testes.
-Typically causes decreased fertility and some cognitive challenges.

DNA fingerprinting is a method utilized for identifying individuals by analyzing their distinctive DNA sequences. The accurate sequence of steps in DNA fingerprinting includes:
1. DNA Isolation (Step - b): DNA is isolated from sources such as blood, hair roots, or saliva through chemical processes that disrupt cell membranes.
2. Restriction Digestion (Step - d): Specific restriction enzymes are used to cut the isolated DNA at precise sequences, resulting in fragments of varying lengths.
3. Gel Electrophoresis (Step - a): These DNA fragments are sorted by size using agarose gel electrophoresis, where negatively charged DNA moves towards the positive electrode, allowing smaller fragments to travel faster.
4. Southern Blotting (Step - c): The DNA fragments are then blotted onto a nylon membrane from the gel, and specific sequences are identified using a radioactive or fluorescent DNA probe.
5. Visualization and Analysis (Step - not listed but essential): DNA patterns are revealed through autoradiography on X-ray film, creating a DNA fingerprint used in forensic science, paternity tests, and genetic research.

(b) Isolation of DNA → (d) Restriction digestion → (a) Gel electrophoresis → (c) Southern blotting