Question

Some traits are considered to be quantitative even though phenotypes are classified only as present or absent. Genetic diseases often fit this description. What is the term used to describe this type of trait?

A. polygenic trait
B. threshold trait
C. meristic trait
D. epistatic trait
E. environmental trait

Answer 1

A 'threshold trait' is the term used for traits that are phenotypically simple (present or absent) but are quantitatively complex, typically influenced by multiple genes and environmental factors.

Step-by-step explanation:

The term used to describe traits that show a simple presence or absence in the phenotype but are the result of the cumulative effect of many genes is known as a threshold trait. These traits appear to be simple Mendelian traits, but they are actually quantitative, meaning they are influenced by multiple genetic and sometimes environmental factors. Once a certain threshold of these factors is surpassed, the trait becomes expressed in the organism. This concept is widely applicable in the study of genetic diseases, which may show up in an individual only when a certain genetic load has been reached.

Most human traits are polygenic, not Mendelian, meaning that they are determined by more than one gene, as is the case with height, skin color, and weight. Moreover, polygenic traits are often characterized by a wide range of variability and can also be influenced by environmental factors. The complexity of these traits adds to the genetic diversity which is crucial for the survival of a species.

Answer 2

The correct answer is option B. threshold trait.

Explanation:

Quantitative characteristics that are separately expressed in a limited (mostly two) number of physical character or phenotype but phenotypes are classified only as absent or present.

Usually these traits, their inheritance is determined by the environment and multiple genes. Genetics diseases such as the onset of diabetes are generally fit with this description of the threshold trait.

Thus, the correct answer is option B.