Our understanding of the role played by genes in many human characteristics - for example, body size, performance on IQ tests, and personality traits - is advancing rapidly. In this new genetic era, the role of the environment .

is to work with genes in complex and often unknown ways in the development of these traits.

Explanation:

The development as well as the expression of the traits in a living being depends upon both genes and the environmental factors. The heredity traits as well as the environmental factors both are responsible for the expression of the traits in the living beings.

Relatively how genes express their traits is dependent upon in the environment they are present. Sometimes, the environment restricts the expression of genes. The effects of the environment depends upon the genes with which they interact with.

For example, the people may vary in height. The environmental factors like proper diet, lack of exercise may suppress the trait of tallness in some living beings. Thus the expression of the gene becomes unknown due to environmental conditions.

the answer is a) cell division.

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