If an individual is trisomic for chromosome 21, resulting in Down syndrome, and has an extra chromosome in each cell, what mutation must have occurred? A nondisjunction mutation in the gamete of one of the parents
A nondisjunction in both gametes of the parents
A nondisjunction in one of the first gamete cells of the individual
A nondisjunction mutation in body cells of both parents

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.

d. planting trees

the trees take in carbon to make oxygen.