Are some people more 'attractive' to mosquitos? If so, is that a hereditary trait?
There is a genetic component to mosquito's attraction to humans.


  Female mosquitoes display preferences for certain individuals over others, which is determined by differences in volatile chemicals produced by the human body and detected by mosquitoes. ... Overall, there was a strong narrow-sense heritability of 0.62 (SE 0.124) for relative attraction and 0.67 (0.354) for flight activity based on the average of ten measurements. The results demonstrate an underlying genetic component detectable by mosquitoes through olfaction.


--Heritability of Attractiveness to Mosquitoes


  However, analysis of a comparative rating variable "compared with your twin, who is bitten by mosquitoes more often?" indicated a strong genetic influence on frequency of being bitten by mosquitoes, with no significant differences observed between males and females. 


--Twin study of adolescent genetic susceptibility to mosquito bites using ordinal and comparative rating data.

There are many other influences on how attractive people are to mosquitos, including diet, alcohol consumption, and various disease conditions.