HIS, HERS, THEIR OR ONE’S?
In English, there are no apparent differences between genders in these types of sentences.
Somebody was here. His trails can be seen around the house.
Use of adjective “his” may suggest a person with masculine gender, because the word “somebody” does not have male gender.
You can apply to both grammar and political correctness:
Somebody was here. His or her footprints can be seen around the house.
You can also express it correctly politically but not entirely correctly grammatically:
Somebody was here. Their footprints can be seen around the house.
As form “his or her” sounds quite artificially then usually possessive adjective in the plural (their) is used in a colloquial speech.
Would someone lend me their pen?
No one could remember their numbers.
Likewise with the impersonal pronoun “one”.
Theoretically, once used should be consistently used in the whole sentence.
One should always wash one’s hands before meals.
However, often “one’s” is replaced with “their”, albeit a sentence developed this way is not grammatically correct.
One should always wash their hands before meals.
In case of doubts, the best way is to use the impersonal pronoun “you.”
When it comes to nouns, use the plural to keep the sentence correct.
You should always wash your hands before meals.
Should teachers like their students?