Which structure contains the genes and is composed of DNA?

Which structure contains the genes and is composed of DNA?

• A. Chromatids
• B. Chromosomes
• C. Genes
• D. Nucleolus

Answer: (B)

Genes are specific sequences of DNA that code for proteins or RNA. In cells, these gene sequences are organized on long DNA molecules called chromosomes. Chromosomes are the structures whose main role is to carry the organism’s genes, and they are composed of DNA wrapped around proteins, forming a compact, functional unit. Chromatids are duplicated halves of a chromosome, so they also contain genes, but they are parts of a replicated chromosome rather than the single DNA-containing structure that houses the genes in an unreplicated state. The nucleolus is a substructure in the nucleus where ribosomal RNA genes are transcribed and ribosome components assembled, not the DNA carrier of all genes. So the structure that contains the genes and is made of DNA is the chromosome.

Genes are specific sequences of DNA that code for proteins or RNA. In cells, these gene sequences are organized on long DNA molecules called chromosomes. Chromosomes are the structures whose main role is to carry the organism’s genes, and they are composed of DNA wrapped around proteins, forming a compact, functional unit. Chromatids are duplicated halves of a chromosome, so they also contain genes, but they are parts of a replicated chromosome rather than the single DNA-containing structure that houses the genes in an unreplicated state. The nucleolus is a substructure in the nucleus where ribosomal RNA genes are transcribed and ribosome components assembled, not the DNA carrier of all genes. So the structure that contains the genes and is made of DNA is the chromosome.