They use fossils and the Earth's layers to help them which is also an example of geological time. The layers tell them the history by how deep they are along with the fossils. Since the lowest layers, for example, are the oldest, scientists use this to determine Earth's age and history.
Answer:
There are a number of mechanisms through which a bacterial cell might become resistant to a specific antibody.
- Some bacteria might posses a cell membrane which wouldn't allow the transfer of antibiotics into the cell of the bacteria. Some bacterial cells might not have the target sites on which the antibiotics attack. A bacterial cell that would be non-resistant wouldn't block the entry of the drug or it might not lack the site where the drug has to function.
- Some resistant bacteria might produce enzymes that would inactivate the activity of the antibiotics. This enzyme machinery would lack in a non-resistant strain. The resistant bacteria might have undergone mutations over a period of time to evolve a machinery for antibiotic resistance.
The mom could be a carrier of the gene for the disorder and since it's on the X chromosome if they have a boy it would have the disorder. 25% chance