in the "d. pseudoobscura" population, some males have a harmful chromosome called sex ratio (sr), where an inactive y-chromosome is transmitted. if an sr male mates with a female, the female will produce only daughters. monandry allows the spread of sr and increases the extinction risk in species having sr genes because the sr driver can spread quickly, enriching populations for females. polyandry decreases the sr gene frequency because the non-sr male sperm outcompete the sr male sperm. therefore, polyandry results in a decreased risk of extinction in the population.