Gene Flow/ Antibiotic Resistance

Explain gene flow

• movement of alleles between populations

• occurs when individuals leave one population, join another, and breed

• equalizes gene allele frequencies between source and recipient populations

  • homogenizes allele frequencies between populations

  • gene flow makes 2 populations more similar to one another over time

explain the effect of gene flow on genetic variation

increases genetic variation within populations by introducing new alleles, but it decreases genetic differences between populations by homogenizing them and making their gene pools more similar

explain the effect of gene flow on fitness

gene flow is random with respect to fitness

• gene flow does not always reduce fitness- can increase or decrease

  • can replenish alleles in population that has lost alleles due to genetic drift

  • this should increase genetic diversity

  • it however is common for movement of alleles between populations to reduce genetic differences

explain how gene flow between wild and captive steelhead trout impacted the fitness of wild offspring

Dna tests were conducted to study fitness

• individuals with 2 wild parents

• individuals with 1 wild and 1 captive-bred parent

• individuals with 2 captive-bred parents

Male and female fish with 1 captive-bred parent has 16% lower fitness in comparison to the 2 wild parents.

Male and female fish with 2 captive-bred parents had 38% lower fitness in comparison to the 2 wild parents.

• In both cases, this reduces the fitness of the wild population

• Thus, using captive-bred fish may ultimately decrease population size.

Describe why mutation is a random mechanism of evolution

It is the random production of new alleles, which increases genetic variation by producing NEW alleles. It is random with respect to fitness; most mutations in coding sequences lower fitness. In other words, it does not occur in a way that tends to increase of decrease fitness.

Mutations restores genetic diversity: creates new alleles, not only new combinations of alleles.

explain why mutations do not arise when needed

It just happens. It is the ultimate source of genetic variation. Mutation can be beneficial (rare), neutral, and harmful.

Describe how antibiotics work on bacterial cells, using examples

Antibiotics work by destroying bacteria or preventing them from growing and multiplying, targeting structures or processes essential for bacterial survival, such as cell wall. Humans do not have a cell wall, protein synthesis, and enzyme synthesis, so it does not damage our cells.

Common mechanisms include disrupting the bacterial cell wall, interfering with protein synthesis by targeting ribosomes, and damaging the cell's DNA. Examples include penicillin.

Example: Take a 14 day dose, antibiotics will work on both harmful and harmless bacteria in ones body. If you take the prescribed dosage, the target bacteria population will be greatly reduced and the growth of the remaining bacteria will be held in check by competition with other types of bacteria. 

Explain why antibiotics are effective in treating bacterial infections, but not viral infections

Antibiotics target specific processes in bacteria that viruses lack, making them ineffective against viral infections.

Bacteria are single-celled organisms that can grow and reproduce independently, and antibiotics exploit their unique features, such as their cell walls or ribosomes, to kill them or inhibit their growth. In contrast, viruses are not cells and require a host cell to replicate, meaning there are no similar structures for antibiotics to target.

Describe why human cells don’t become resistant to antibiotics

They target structures that are unique to bacteria, that humans do not have.

• bacteria cell wall

• ribosomes (which are different from eukaryotic ribosomes)

• or specific bacterial enzymes

Resistance is a process that occurs in the bacteria, not the human host.

Explain why taking the full prescribed course of antibiotics is important.

The many bacterial cells still alive are the most resistant to the antibiotic. They are the founders of a new population, and the next time the patient takes the drug, it will be ineffective.

The bacteria cells will create more and remain resistant, so it will be ineffective, and could cause the infection to come back.

Differentiate between bacteria resistant to penicillin, MRSA, and VRSA

Penicillin-resistant bacteria are not susceptible to penicillin and related drugs. MRSA, is a specific type of bacteria resistant to a broad class of antibiotics, which includes penicillin. VRSA is a strain of MRSA that has further developed resistance specifically to vancomycin, a powerful antibiotic often used for serious infections.

When penicillin stopped working, people switched to an antibiotic called methicillian. As the bacteria evolved, doctors had to treat the bacteria with vancomycin. It has evolved 14 times, but currently VRSA cannot spread from person to person like MRSA can. 

Penicillin is an antibiotic. MRSA is a virus. VRSA is resistant to methicillian.

Explain how the evolution of antibiotic resistance is an example of natural selection

Rise of rifampin resistance in TB

Antibiotics act as a selective pressure, favoring bacteria with advantageous genetic mutations that make them resistant. When an antibiotic is introduced, it kills the susceptible bacteria, but the resistant bacteria survive and reproduce, passing their resistance genes to their offspring. Over generations, the population shifts to become predominantly resistant.

1) Large populations of TB bacteria found in patients lungs, makes him sick. A few of the bacteria cells happen to have a point mutation in the rpoB gene (one base is changed).

2) Drug therapy begins killing most of the TB. Patient seems cured and the drug therapy is ended.

3) The mutant cells proliferate (increase rapidly in numbers), resulting in another major infection of the lungs. The patient becomes sick again.

4) A second round of drug therapy begins, but is ineffective on the drug resistant bacteria. The patient dies.

Predict how the overuse of antibiotics can influence natural selection in bacteria

The overuse of antibiotics drives natural selection in bacteria by creating a powerful selective pressure that favors bacteria with drug-resistant traits.

Instead of killing all bacteria, antibiotic misuse ensures that the only ones that survive and reproduce are those with the specific genetic variations that enable them to resist the drug.

This is a classic demonstration of the "survival of the fittest.”