Species variation: which animals naturally produce heavy-chain–only antibodies lacking light chains? Identify the species known to have functional immunoglobulins without light chains.

Introduction / Context:
Most vertebrate antibodies are composed of two heavy and two light chains. However, certain species have evolved heavy-chain–only antibodies with distinctive properties. Recognizing these natural variations is important in antibody engineering and nanobody technology.

Given Data / Assumptions:

• Camelids (for example, camels, llamas, alpacas) produce heavy-chain–only antibodies in addition to conventional IgG.
• These heavy-chain antibodies lack the light chain and CH1 domain.
• Their single variable domain (VHH) forms the basis of “nanobodies.”

Concept / Approach:
The absence of light chains does not prevent antigen recognition because the VHH domain is soluble and stable. The small size allows access to recessed epitopes and simplifies recombinant expression.

Step-by-Step Solution:
Recall which taxa naturally produce heavy-chain–only IgG: camelids are the classic example.Exclude humans, cows, and buffalo, which make conventional Ig composed of heavy and light chains.Select camels as the correct representative species.

Verification / Alternative check:
Structural and genetic studies show camelid IgG2/IgG3 subclasses lacking light chains; llama VHH domains are routinely used as research tools.

Why Other Options Are Wrong:
Humans and bovines do not naturally produce heavy-chain–only antibodies as a dominant class. Chickens produce IgY with light chains, not heavy-chain–only antibodies.

Common Pitfalls:
Confusing heavy-chain–only antibodies with engineered single-chain variable fragments (scFv); scFv are artificial fusions of VH and VL connected by a linker.

Final Answer:
Camels.