AP Syllabus focus:
‘Genetic information is stored and transmitted between generations primarily by DNA molecules and, in some organisms, by RNA.’
Genetic information is the biological “instruction set” that cells copy, pass on, and use to build functional molecules. In AP Biology, this topic emphasizes how DNA usually carries heredity, while RNA can serve that role in some organisms.
What “genetic information” means
Genetic information is encoded in the sequence of nucleotides in a nucleic acid polymer. A nucleotide sequence can be copied (to transmit information) and read (to produce functional products that affect phenotype).
Gene: A segment of nucleic acid whose nucleotide sequence carries information to produce a functional RNA and/or a polypeptide (often via an RNA intermediate).
Although genes are often discussed individually, organisms also store genetic information at larger scales (all genes plus noncoding regions), enabling coordinated inheritance of many traits.
Key idea: information is in the order
The order of nucleotides is the code.
Copying that order with high fidelity allows continuity across cell divisions and generations.
Changes in order (mutations) can alter the information passed on.
DNA as the primary hereditary molecule
For cellular life, DNA (deoxyribonucleic acid) is the primary long-term storage molecule for genetic information because its chemical structure supports stability and accurate copying.
Why DNA is well-suited for long-term storage
Double-stranded structure provides a built-in reference: each strand can serve as a template for copying the other.
This diagram shows a DNA replication fork, highlighting how antiparallel strands are copied in different ways: the leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously as Okazaki fragments. The labeled RNA primers emphasize that DNA polymerase extends from an existing 3′-OH rather than starting synthesis de novo. Source
Deoxyribose sugar (lacking a 2' hydroxyl group) makes DNA less chemically reactive than RNA, improving stability.
Many organisms maintain DNA with repair pathways that correct damage or copying errors, preserving information.
Genome: The complete set of genetic information in an organism or virus, encoded in its nucleic acid (DNA for most cellular organisms; DNA or RNA for viruses).
DNA’s role in transmission is reflected in reproduction: during cell division and across generations, DNA is replicated so descendants inherit essentially the same nucleotide sequences, with variation arising from occasional changes.
DNA and inheritance across generations
In sexually reproducing organisms, DNA is transmitted via gametes, combining parental genetic information.
In asexual reproduction, descendants inherit DNA largely as a copy of the parent’s DNA.
In both cases, sequence continuity is the foundation of heredity.
RNA as genetic material in some organisms
The syllabus highlights an important exception: in some organisms, especially many viruses, genetic information is stored and transmitted by RNA (ribonucleic acid) rather than DNA.
When RNA carries the genome
Some viruses package RNA genomes and rely on host cells to replicate and express that information.
This schematic summarizes the replication logic of positive-sense ssRNA viruses: the incoming (+)RNA can function as mRNA for immediate translation, then serves as a template to produce a complementary (−)RNA intermediate. The (−)RNA intermediate is then copied to generate many new (+)RNA genomes for further translation or packaging into new virions. Source
RNA genomes can be single-stranded or double-stranded, depending on the virus.
Because replication strategies differ among viruses, “RNA as genetic material” refers to RNA serving as the inherited template passed between viral generations.
This exception reinforces the broader principle: nucleic acids (DNA or RNA) can store information as nucleotide sequences, provided they can be faithfully copied and passed on.
Tradeoffs of RNA as hereditary material
RNA is generally less chemically stable than DNA due to the 2' hydroxyl group, making it more prone to hydrolysis.
Many RNA-replicating systems show higher mutation rates, which can accelerate evolution of viral populations.
Despite instability, RNA genomes can be advantageous when rapid adaptation improves survival in changing host environments.
Shared features that enable information storage and transmission
Both DNA and RNA are nucleic acids built from nucleotides, and both can encode inheritable information.
This figure illustrates the three-part structure of a nucleotide: a pentose sugar, a phosphate group, and a nitrogenous base. It also labels the sugar’s carbon numbering (1′–5′), which helps explain how nucleotides link via phosphodiester bonds to form a directional polymer (5′→3′) whose base sequence encodes genetic information. Source
Nucleotide: A monomer of nucleic acids consisting of a sugar, a phosphate group, and a nitrogenous base; nucleic acid information is encoded by the sequence of bases.
A core AP Biology theme is that sequence → information → inheritance:
Sequence can be copied (transmission).
Sequence can be read to produce functional products (expression).
Transmission across generations preserves traits while allowing variation.
Information transfer vs. information storage
It is helpful to separate two roles:
Storage: Long-term retention of genetic instructions (primarily DNA in cellular organisms; RNA in some organisms).
Transmission: Passing the instructions to offspring or progeny (DNA via reproduction; RNA genomes via viral replication and spread).
Both roles depend on the same central property: a polymer whose monomer order can be precisely replicated.
FAQ
Key evidence came from classic experiments showing that hereditary traits could be transferred by purified DNA and that DNA, not protein, correlated with inheritance.
Further support included the predictable relationship between DNA sequence changes and heritable trait changes.
RNA viruses carry or encode enzymes that copy RNA from RNA templates, or they use host machinery in specialised ways.
Different RNA virus groups use different strategies depending on whether their genome is positive-sense, negative-sense, or double-stranded RNA.
Known cellular life stores its genome as DNA; RNA genomes are characteristic of many viruses.
Some cellular elements use RNA intermediates extensively, but the stable, heritable genome remains DNA.
RNA replication systems often have less proofreading, increasing mutation rates.
High replication numbers plus mutation can generate diverse viral populations, enabling selection to act quickly.
Cells use multiple layers of protection, including enzymatic repair pathways, damage recognition, and controlled cell cycle checkpoints.
Viruses vary widely; some rely on rapid replication and selection rather than extensive repair.
Practice Questions
State where genetic information is stored in most organisms and identify one type of organism in which RNA stores genetic information. (2 marks)
DNA is the primary hereditary molecule in most organisms (1).
RNA serves as genetic material in some organisms, e.g. RNA viruses (1).
Explain how nucleic acids can store and transmit genetic information between generations, and compare why DNA is used in most organisms whereas RNA is used in some organisms. (6 marks)
Genetic information is encoded in the sequence/order of nucleotides (1).
Transmission requires copying the nucleic acid sequence so descendants/progeny inherit the information (1).
DNA is generally double-stranded, allowing templated copying using complementary strands (1).
DNA is chemically more stable than RNA (e.g. deoxyribose lacks 2'-), supporting long-term storage (1).
RNA can function as genetic material in some organisms (e.g. viruses) where the RNA genome itself is inherited (1).
RNA genomes often have higher mutation rates, which can enable faster adaptation in some contexts (1).
