If crossing over did not occur, how could the passing on of physical features be affected?

Crossing over is the process by which genetic variations occur. The homologous chromosomes exchange segments of DNA which allow the genetic variations to occur. If crossing over did not occur then there would be reduced genetic variations. The offsprings will have each chromosome identical to either the male or the female chromosome. Hence, the phenomenon of crossing over and independent assortment both are very important to ensure the genetic variations.  

then that particular organisms become extinct.