You're talking about Heterochromia iridum. Hetero comes from Greek, meaning "different" or "other", chromia comes from the Greek chrom, meaning colour, and iridium comes from iris, which is the coloured part of your eye. (heterochromia iridium literally means different-coloured irises)
It can be genetic transmitted(it's a dominant trait, and is not related to gender/sex), but can also be acquired, sometimes due to injury or tumours. It is caused by a difference in pigment in the iris, and there are many ways that this expression can happen. (It could be too dark, too light, it could be the whole iris, or just parts). My educated guess it that this complexity of potential causes would likely make it difficult to pin to one chromosome.
Heterochromia iridium is the scientific name for two different color eyes in the same individual and while it is relatively rare in humans it is actually common in some animals such as horses, cats, and some species of dogs. When an individual has a variety of colors within a single iris it is called heterchromia iridis which is a variation of heterchromia iridum.
Eye color is determined by the amount of melanin present in the iris. As melanin is a dark brown pigment, blue eyes are due to a lack of melanin and brown eyes indicate melanin-rich irises. People with darker hair and skin have higher levels of melanin and generally have brown eyes. On the other hand, people with lighter hair and skin have lower levels of melanin and usually have lighter colored eyes.
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