Definition — What is a gene? Choose the most complete description reflecting classical and molecular genetics.
-
AThe functional unit of inheritance
-
BA fragment of DNA that encodes a functional product
-
CA portion of a chromosome
-
DAll of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:“Gene” has evolved from a conceptual unit of heredity to a molecular entity encoded in DNA. Modern definitions reconcile function (heritable trait), structure (DNA sequence), and genomic context (chromosomal locus).
Given Data / Assumptions:
- Genes are located on chromosomes.
- Genes are DNA sequences that encode functional RNA or protein products.
- Genes act as heritable units influencing phenotype.
Concept / Approach:Each option captures a correct facet. Classical genetics emphasizes “unit of inheritance.” Molecular biology defines genes as DNA segments specifying products (protein or functional RNA). Cytogenetics places genes along chromosomes; thus “all of the above” integrates the perspectives.
Step-by-Step Solution:
Evaluate option A (functional unit): correct by Mendelian definition.Evaluate option B (DNA fragment encoding product): correct by molecular definition.Evaluate option C (portion of a chromosome): correct by physical localization.Integrate: choose the comprehensive option.Verification / Alternative check:Genome annotation treats genes as distinct loci with coordinates, transcripts, and products; inheritance studies link alleles at these loci to traits.
Why Other Options Are Wrong:
- Each single statement is incomplete alone; only the combined statement encompasses function, structure, and location.
Common Pitfalls:Assuming genes must code for proteins only; many genes produce functional RNAs (rRNA, tRNA, lncRNA, microRNA).
Final Answer:All of the above