Add labels to the figure that follows, which illustrates how Mycobacterium tuberculosis evolves when it is exposed to an antibiotic.

Verified step by step guidance

1. Step 1: Observe the first image (A) in the figure. It represents the initial population of Mycobacterium tuberculosis, which includes a mix of antibiotic-susceptible and antibiotic-resistant variants. The red, yellow, blue, and green circles symbolize different bacterial variants.
2. Step 2: Note the process labeled 'Treatment with an antibiotic.' This step involves applying an antibiotic to the bacterial population. Antibiotic-susceptible variants (e.g., red and green) are killed, as indicated by the 'X' marks over them in the second image.
3. Step 3: In the second image, observe that some variants (e.g., yellow and blue) survive the antibiotic treatment. These surviving variants are likely antibiotic-resistant strains.
4. Step 4: In the final image (B), the surviving antibiotic-resistant variants (yellow and blue) proliferate, leading to a population dominated by resistant bacteria. This demonstrates the process of natural selection, where resistant variants survive and reproduce.
5. Step 5: Label the figure accordingly: (A) 'Initial population with both antibiotic-susceptible and antibiotic-resistant variants,' (middle) 'Antibiotic treatment eliminates susceptible variants,' and (B) 'Population dominated by antibiotic-resistant variants after treatment.'

Key Concepts

Antibiotic Resistance

Antibiotic resistance occurs when bacteria evolve mechanisms to withstand the effects of drugs that once killed them or inhibited their growth. This can happen through genetic mutations or acquiring resistance genes from other bacteria. In the context of Mycobacterium tuberculosis, exposure to antibiotics can lead to the survival of resistant strains, complicating treatment efforts.

Natural Selection

Natural selection is a fundamental mechanism of evolution where organisms better adapted to their environment tend to survive and reproduce more than those less adapted. In the case of antibiotic treatment, bacteria that possess mutations allowing them to survive the antibiotic will proliferate, leading to a population dominated by resistant variants, as illustrated in the figure.

Mutation and Variation

Mutation refers to changes in the DNA sequence of an organism, which can lead to variations in traits. In bacteria like Mycobacterium tuberculosis, mutations can confer advantages such as antibiotic resistance. The presence of genetic variation within a bacterial population is crucial for natural selection to occur, as it provides the raw material for evolution in response to environmental pressures like antibiotic treatment.