Understanding the Difference Between "Vary with Kind" and "Vary with Degree"

 

Vary with Kind

"Vary with kind" refers to qualitative variation, where traits are classified into distinct, non-overlapping categories. These traits are often governed by a small number of genes, sometimes even a single gene, and do not exhibit a continuous range of variation.

Examples:

• Flower Color: Flowers may be red, white, or yellow, with each color representing a distinct category.
• Seed Shape: Seeds can be either round or wrinkled.
• Disease Resistance: Plants may be resistant or susceptible to a particular disease.

Characteristics:

• Discrete Categories: Traits fall into separate, well-defined groups.
• Simple Inheritance: Usually controlled by one or a few genes, often following Mendelian inheritance.
• Qualitative Traits: The variation is in kind rather than amount, making classification straightforward.

Vary with Degree

"Vary with degree" refers to quantitative variation, where traits show a continuous range of values rather than distinct categories. These traits are usually influenced by multiple genes (polygenic inheritance) and are also affected by environmental factors.

Examples:

• Plant Height: Heights vary continuously from short to tall with many intermediate values.
• Grain Yield: Yield can range from low to high with numerous possible values in between.
• Leaf Size: Leaves may vary in size from small to large along a continuum.

Characteristics:

• Continuous Variation: Traits exhibit a smooth distribution, often following a bell-shaped curve (normal distribution) within a population.
• Polygenic Inheritance: Controlled by multiple genes, each contributing incrementally.
• Quantitative Traits: These traits vary in amount or degree rather than forming distinct types.

Application in Plant Breeding

Understanding whether a trait varies with kind or degree is crucial in plant breeding, as it determines the best selection strategy.

Qualitative Traits (Vary with Kind)

• Selection: Straightforward breeding programs can easily select for or against specific trait categories.
• Marker-Assisted Selection (MAS): Molecular markers linked to genes controlling these traits can be used to facilitate selection.

Quantitative Traits (Vary with Degree)

• Selection: Requires advanced statistical methods, such as estimated breeding values, for effective selection.
• Genomic Selection (GS): Utilizes genome-wide marker data to predict the performance of individuals based on their genetic makeup.
• Environmental Influence: Environmental factors and genotype-environment interactions must be considered when selecting for these traits.

Conclusion

In plant breeding, recognizing whether a trait "varies with kind" or "varies with degree" helps in choosing the appropriate breeding strategies. Qualitative traits are managed using straightforward selection methods, while quantitative traits require complex approaches, including statistical and genomic tools, to achieve desired breeding outcomes.