When analyzing three genes that reside on the same chromosome, the expected frequency of double-crossover events can be determined by multiplying the frequency of single crossovers between each pair of genes. What would cause the number of observed double-crossover events to be less than the expected value?

sulfur dioxide

explanation: acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. these substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.

the answer would be   10%