Marco sembra un genio.

Because sembrare means to seem or to appear, while essere means to be.

So:

• Marco è un genio = Marco is a genius
• Marco sembra un genio = Marco seems like a genius

The Italian sentence suggests an impression or appearance, not a definite statement of fact.

In English, we often say seems like a genius, but in Italian sembrare can connect directly to a noun or adjective without an extra word.

So Italian says:

• Marco sembra un genio
• literally: Marco seems a genius

This is completely normal in Italian. You do not need a separate word for like here.

Un is the masculine singular indefinite article, meaning a or an.

So:

• un genio = a genius

Because genio is a masculine singular noun, un is the correct article.

Because genio and geniale are different kinds of words:

• genio = a noun = genius
• geniale = an adjective = brilliant / ingenious

So:

• Marco sembra un genio = Marco seems a genius
• Marco sembra geniale = Marco seems brilliant

Both are correct, but they mean slightly different things.

Because Marco is a proper name, and in standard Italian proper names usually do not take an article.

So you normally say:

• Marco sembra un genio

not:

• Il Marco sembra un genio

In some regional varieties of Italian, people do use articles with names in everyday speech, but that is not the standard form you should learn first.

Because sembra is the third-person singular form of sembrare in the present tense.

The present tense is:

• io sembro = I seem
• tu sembri = you seem
• lui/lei sembra = he/she seems
• noi sembriamo = we seem
• voi sembrate = you all seem
• loro sembrano = they seem

Since the subject is Marco, you use sembra.

Yes, very often.

Examples:

• Marco sembra stanco = Marco seems tired
• Marco sembra intelligente = Marco seems intelligent
• Marco sembra felice = Marco seems happy

So sembrare can be followed by:

• a noun: un genio
• an adjective: geniale, intelligente, stanco

Put non before the verb:

• Marco non sembra un genio.

That means Marco doesn’t seem like a genius.

This is the normal way to negate a sentence in Italian.

In everyday Italian, you usually keep the same word order and use intonation:

• Marco sembra un genio?

This means Does Marco seem like a genius?

In writing, the question mark shows it clearly. In speech, your voice rises at the end.

As a noun, genio is grammatically masculine:

• un genio = a genius
• il genio = the genius

If you are talking about a female person, Italian often still uses un genio to describe her, because the noun itself is masculine in form. In real usage, context matters, and speakers may choose different phrasing depending on style and register.

For a beginner, the key thing is:

• genio is treated as a masculine noun
• so it takes un, not una

Genio is pronounced roughly like JEH-nyo.

A few pronunciation notes:

• g before e sounds like the j in job
• ge = jeh
• nio here sounds like nyo

So:

• genio ≈ JEH-nyo
• sembra ≈ SEM-bra

Not exact English sounds, of course, but that is a useful approximation.

It could be either, depending on context and tone.

• Said sincerely, Marco sembra un genio can mean Marco appears very smart.
• Said sarcastically, it can mean the opposite, like Yeah, Marco really seems like a genius...

Italian, like English, often relies on tone of voice and situation to show irony.