Question

The paradigm in vertebrates is that, once sex determination occurs and testes or ovaries are formed, secondary sexual differentiation (male vs. female characteristics) is dependent on male or female hormones that are produced. Recently, D. Zhao and colleagues studied three chickens that were bilateral gynandromorphs, with the right side of the body being clearly female and the left side of the body clearly male [Nature 464 : \(237(2010)] .\) Propose experimental questions that can be investigated using these chickens to test this paradigm. What alternative interpretation contrasts with the paradigm?

Short answer

Answer: Experimental questions that can be investigated using bilateral gynandromorph chickens include: i. Differences in hormone production between the male and female sides of their bodies ii. Factors other than hormones that may determine secondary sexual characteristics iii. Interaction between the male and female sides of the organism affecting sexual differentiation iv. Independent functioning of the male and female sides with respect to hormones and secondary sexual characteristics. An alternative interpretation that contrasts with the paradigm is that secondary sexual differentiation in bilateral gynandromorph chickens may not solely depend on hormone production in the testes and ovaries, but other factors such as genetics or the environment may influence their sexual differentiation.

Step-by-step solution

1. Understanding the paradigm and its concepts in vertebrates

The paradigm in vertebrates states that once sex determination occurs and testes or ovaries are formed, secondary sexual differentiation (male vs. female characteristics) is dependent on male or female hormones that are produced.

2. Observing the bilateral gynandromorph chickens

Zhao and colleagues observed three chickens that were bilateral gynandromorphs, meaning that the right side of their bodies was clearly female, and the left side was clearly male. This unique characteristic allows for testing the current paradigm of secondary sexual differentiation within the same organism.

3. Proposing experimental questions to test the paradigm

Possible experimental questions include: i. Do the bilateral gynandromorph chickens exhibit differences in hormone production between the male and female sides of their bodies? ii. Are the secondary sexual characteristics determined exclusively by hormone levels, or are there other factors at play in these chickens? iii. Is there any interaction between the male and female sides of the organism that may affect sexual differentiation? iv. Do the male and female sides of the bilateral gynandromorph chickens function independently with respect to hormones and secondary sexual characteristics?

4. Alternative interpretation

An alternative interpretation that contrasts with the paradigm is that the bilateral gynandromorph chickens' secondary sexual differentiation may not solely depend on hormone production in the testes and ovaries. It is possible that other factors, such as genetics or the environment in which these chickens develop, may influence their sexual differentiation. The existence of bilateral gynandromorph chickens challenges the idea that hormones are the exclusive determinant of secondary sexual characteristics in vertebrates.

Key concepts

Secondary Sexual Differentiation

Secondary sexual differentiation refers to the development of physical characteristics that distinguish male from female organisms beyond the gonads. In vertebrates, this typically involves features like the male mane in lions or the presence of mammary glands in female mammals. These characteristics are largely influenced by hormones like testosterone and estrogen. The standard view in vertebrates is that secondary sexual differentiation occurs after the formation of the gonads, when these hormones are produced.
Hormones are pivotal in this process as they drive changes such as body size, feather color, or the presence of specific reproductive organs. However, biology can be surprisingly complex, as seen in cases like bilateral gynandromorphs, which provides evidence that there might be more to the story than hormone production alone. By studying such instances, scientists can explore if other factors also play a role in these processes.

Hormone Production

Hormones are crucial molecules in the body that act as messenger substances, communicating signals from the endocrine system to various parts of the organism.
They are produced by glands such as the testes and ovaries, and facilitate the development of primary and secondary sexual traits. Testosterone, for example, is typically associated with male development, impacting attributes such as muscle mass and body hair.

• Testosterone - influences male characteristics.
• Estrogen - plays a key role in female traits.

The interaction of these hormones can create a mosaic of sexual characteristics in organisms, known as secondary sexual differentiation.
In bilateral gynandromorphs, studying hormone levels could provide insights into whether these hormones function independently in different body parts, or if there are other mechanisms at play.

Bilateral Gynandromorphs

Bilateral gynandromorphs are fascinating examples of sexual differentiation, typically seen in birds and insects. These organisms exhibit both male and female characteristics simultaneously, split along their bodies.
For example, Zhao and colleagues studied chickens with one side showing male features and the other female. This rare phenomenon presents a unique opportunity to study the mechanisms behind sexual differentiation.
There are experimental questions that can be prompted by this condition, such as whether the two halves produce different hormone levels or how each side's sexual characteristics develop. It challenges the prevailing idea that hormones from the gonads entirely dictate secondary sexual features. Bilateral gynandromorphs provoke scientists to reconsider how sex determination and differentiation occur in more complex ways.

Genetic and Environmental Influence

Beyond hormonal influences, sex determination and differentiation might also be affected by genetic and environmental factors. These influences might explain certain characteristics observed in bilateral gynandromorphs.

• Genetic factors - involve variations at the chromosomal level, which might dictate sexual phenotypes independently of hormones.
• Environmental influences - include conditions such as temperature, which impact the development in some reptiles and potentially birds.

The study of bilateral gynandromorphs can bring light to how these non-hormonal factors contribute to the development of sexual characteristics, prompting reevaluation of existing biological paradigms. This creates a broader understanding of how various factors interplay in the fascinating process of sexual differentiation.