A mutation is a change in DNA, the hereditary material of life. An organism's DNA affects how it looks, how it behaves, and its physiology.
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Scientists combine several well-tested techniques to find out the ages of fossils. The most important are Relative Dating, in which fossils and layers of rock are placed in order from older to younger, and Radiometric Dating, which allows the actual ages of certain types of rock to be calculated. Relative Dating.
Answer:
Size of the drug molecule
Maternal plasma concentration
Degree of ionisation
Explanation:
Size of the drug molecule
Most drug molecules, including alcohol, nicotine and caffeine, are small enough to enter milk. Exceptions are drugs with high molecular weights such as heparins and insulin.
Maternal plasma concentration
Passive diffusion is the primary pathway by which drugs enter milk. There is a good concordance between the time-course of maternal plasma-drug concentration and milk-drug concentration. Maternal plasma concentration is also affected by the drug’s distribution into different tissues. A high volume of distribution (as for sertraline) will contribute to a lower maternal plasma concentration and a subsequent lower concentration in milk.
Degree of ionisation
Drugs cross membranes in an un-ionised form. Milk is generally slightly more acidic (pH 7.2) than the mother’s plasma (pH 7.4) so it attracts weak organic bases such as oxycodone and codeine.7 Such drugs become ionised and ‘trapped’ in the milk. Conversely, weak organic acids such as penicillin tend to be ionised and held in maternal plasma.