Question

different l. lactis bacteria are better at fermenting different types of sugars. some l. lactis have polysaccharide - specific fermentation, so they can ferment large sugar molecules called polysaccharides but not a small sugar molecule called lactose. other l. lactis have lactose - specific fermentation; they can ferment lactose, which is found in milk, but cannot ferment polysaccharides. lactose - specific fermentation is useful for humans: it helps turn milk into cheese!
the l. lactis bacterias environment changed to have fewer polysaccharides than lactose sugars. after this change, over a time period long enough for natural selection to occur, the percentage of the l. lactis population with lactose - specific fermentation increased.
use the theory of natural selection to construct a possible explanation for how the l. lactis population adapted to its changed environment.
having lactose - specific fermentation was ▼ advantageous than having polysaccharide - specific fermentation after the environment changed. so the alleles for polysaccharide - specific fermentation were passed on with ▼ frequency than the alleles for lactose - specific fermentation. as a result, the proportion of the population with polysaccharide - specific fermentation ▼. over time, the population adapted such that a ▼ percentage of bacteria were dependent on the less abundant sugar.

Explanation:

Natural selection favors traits that enhance survival and reproduction. With more lactose (a sugar) available, lactose - specific fermentation (a trait) becomes advantageous. Bacteria with this trait are more likely to survive, reproduce, and pass on their alleles. Bacteria with polysaccharide - specific fermentation (a less useful trait in this new environment) are less likely to pass on their alleles. Over time, the proportion of bacteria with the advantageous trait (lactose - specific fermentation) increases, and the proportion with the less - advantageous trait (polysaccharide - specific fermentation) decreases.

Answer:

Having lactose - specific fermentation was more advantageous than having polysaccharide - specific fermentation after the environment changed. So the alleles for polysaccharide - specific fermentation were passed on with lower frequency than the alleles for lactose - specific fermentation. As a result, the proportion of the population with polysaccharide - specific fermentation decreased. Over time, the population adapted such that a smaller percentage of bacteria were dependent on the less abundant sugar.