What is a tetrad ?
a. another term for a sperm cell
b. a chromatid before meiosis
c. two sets of sister chromatids
d. a haploid cell produced by meiosis
c two sets of sister chromatids

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.

answer: c

explanation:

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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.