The opinion on intelligence being hereditary seems to be divided. Some believe it to be true while some do not.
According to the Genetics Home Reference , intelligence does actually transfer hereditary but there are other factors in the play too. Besides being genetically transferred, intelligence also depends upon environmental factors.
According to various studies, it was suggested and estimated that 50% of intelligence is hereditary, meaning, it transfers from parents to kids, and the rest is acquired and depends on factors such as parenting, nutrition, education, learning resources etc.
There definitely is no concrete answer to this question. To understand it better and help drawing a conclusion, let's have a look at the family line of one of the most important scientist: the Einstein family.
Albert Einstein had an IQ of 160 but did his descendants had the same? Not all of them. In fact, none of them equalled to his excellence. Here's where genetics and environmental factors along with nurturing come into play.
The first reason that genetics didn't span out much for the Einstein family is because kids inherit intelligence as a result of both their parent's IQ.
Mileva Maric , who was a wife to Einstein and mother of her kids didn't have an IQ even close to that of her husband. However, she was a skilled mathematician and had contributed a lot in Einstein's works.
So, the kids inherited a combination of genes from both the mother and the father which is why they couldn't match up to their father's IQ.
Another problem that hit the Einstein family hard was health conditions. Einstein had three kids. Lieserl was the youngest but not much can be spoken about her intelligence because she passed away when she was only one.
Eduard looked promising as he was doing good as a medical student but soon got hit with schizophrenia and was admitted to different mental institutions for a large part of his life. This, obviously, deeply decreased his cognitive abilities.
Hans Albert Einstein, one of this most famous children, grew up to be successful. He got appointed as a teacher at UC Berkeley and was also considered as a pioneer in the field of sediment transport. However, his kids couldn't do much except for one.
Hans had four children but three of them couldn't make it to adulthood. Bernhard, who was the only one to reach adulthood, worked hard and became a physicist with many patents under his name.
Seeing the family line of Einstein, it's quite clear that none of the descendants were on the same mental level as Einstein himself. While there can be many reasons for this, many believe that this happened because they weren't nurtured in a good way, which indicates to how genes are not the only factor that determine intelligence.
Nonetheless, based on this and other similar examples, it can be concluded that genes do play an important role in a person's intelligence as all of Einstein's descendants that reached adulthood made a name for themselves, albeit not as big as Einstein's.