"This is my sister."

[zQqmrCsK]

Could somebody explain why is "je to moje sestra" not good for the answer?

[VladaFu]

Added, it is possible as "This IS my sister.".

[RudigerMarc]

Why is it moje and not mojí or mé? that's what I see in my grammar table under genitiv female singular.

[VladaFu]

This is nominative, not genitive. "Something is something" / "něco je něco" uses the nominative case.

[openminded2]

Why not "Tahle je moje sestra"

[VladaFu]

This is the common "to je"/"je to" pattern. Less common could be "Tohle je moje sestra." but still it stays "to/tohle/toto" for all genders.