What are the disadvantages of sexual and asexual reproduction?

Answer 1

sexual reproduction doesn't yield as many offspring. asexual makes exact replicas, so if one is mutated all its offspring will be too. asexual takes longer for the organism to evolve unless there are helpful mutations.

Answer 2

Because sexual reproduction requires a partner for an organism to be capable of reproducing, a colony of said organisms will die out if there is a lack of fertile partners. However, asexual reproduction does not require a partner, so asexual organisms do not have this problem.

A disadvantage of asexual reproduction can be seen in one of its key features: the offspring produced will be genetically identical to the parent organism. If the parent organism suffers from a genetic defect, then all offspring produced by that organism (and its offspring, etc, etc.) will carry this genetic defect. Sexually reproducing organisms, however, have a greatly diminished risk of inheriting a genetic defect (assuming it is held by only one parent). This is because the offspring inherit a mix of genes from both parents, so with each generation it is likely that any genetic defects present will be "bred out".