Polyploidy is common in plants than in animals because majority of animals  reproduce sexually and the sex determination mechanism involves number and type sex chromosomes. Polyploidy will interfere with this mechanism and hence it is seen rarely in animals. Plants, on the other hand do not have any such sex determination (based on number or type of chromosomes) and can reproduce vegetatively.


When it comes to gene dosage, animals do show gene compensation of X-linked genes by various methods. Example- formation of Barr Body in human females (Note that this has nothing to do with polyploidy, but happens since females have one X chromosome more than males). Whereas gene dosage in polyploid palnts has been exploited for improved agricultural yields as they have shown better productivity than their diploid couterparts.