Problem 9 - Biology of Humans: Concepts, Applications, and Issues

Question

A trait controlled by many genes is described as being ______________.

Step-by-Step Solution

Answer

polygenic

Step 1 - Identify Concepts

Firstly, identify the key terms in the question. The key terms here are 'trait' and 'many genes'.

Step 2 - Understand Genetic Control

Understand that some traits are controlled by a single gene (monogenic), while others are controlled by multiple genes (polygenic).

Step 3 - Define Polygenic Traits

A trait that is controlled by many genes is known as a polygenic trait. Polygenic traits often show a range of phenotypes due to the combined effect of multiple genes.

Step 4 - Conclusion

Based on the understanding from previous steps, complete the sentence.

Key Concepts

Genetic Control

Genetic control refers to how traits are passed from parents to offspring through genes. Genes are segments of DNA that determine specific traits. They exist in pairs and come from both parents. Traits can be influenced by one gene or many genes. This variation in genetic control gives rise to different types of traits and their expression.

In simple terms, genetic control can be understood as:

• Monogenic traits controlled by a single gene.
• Polygenic traits controlled by multiple genes.

Understanding genetic control is important in genetics. It helps explain why some traits are straightforward, while others are complex and show a variety of expressions.

Monogenic vs Polygenic

Traits can be classified based on the number of genes influencing them. This classification is crucial for understanding their complexity.

• Monogenic traits are controlled by a single gene. Examples include blood type and certain inherited diseases. They usually show a clear-cut pattern of inheritance and limited variation among individuals.
• Polygenic traits are controlled by two or more genes. These traits do not follow simple Mendelian inheritance patterns. Examples include height, skin color, and eye color. They often show a wide range of variations because multiple genes contribute to their expression.

In polygenic traits, the effects of individual genes can add up in different ways. This cumulative impact makes predicting the trait expression more complicated compared to monogenic traits.

Range of Phenotypes

Phenotypes refer to the observable characteristics of an organism, like height, skin color, or eye color. The range of phenotypes is the variation in these observable traits.

Polygenic traits tend to show a wide range of phenotypes due to the interaction of multiple genes. Each contributing gene adds a small effect to the overall trait. This leads to continuous variation. For example:

• Human height does not come in just three sizes (short, medium, tall). It ranges continuously due to the combined effect of many genes.
• Skin color also shows continuous variation, influenced by multiple genes contributing to pigment production.

The more genes involved, the greater the range of possible phenotypes. This variation is important for evolutionary processes and environmental adaptability.

Understanding the range of phenotypes helps in studying complex traits and designing genetic research. It also explains why members of the same family can have a wide variety of appearances.