Sex in human embryo is determined by:

The correct option is ‘X’ or ‘Y’ chromosome of sperm.

In humans, the sex of an embryo is determined genetically at the time of fertilization. Let's break down the genetic contribution of both parents to understand why this is the case:

1. Genetic Makeup of Parents:
Females have two 'X' chromosomes (represented as XX). Because they only possess 'X' chromosomes, all eggs (ova) produced by a female will carry a single 'X' chromosome.
Males have one 'X' and one 'Y' chromosome (represented as XY). As a result of meiosis, males produce two types of sperm: approximately 50% of the sperm carry an 'X' chromosome, and the other 50% carry a 'Y' chromosome.

2. The Fertilization Event:
When an egg is fertilized, the sperm determines the sex of the resulting embryo:
If a sperm carrying an 'X' chromosome fertilizes the egg (which always carries an 'X' chromosome), the zygote will have the XX chromosome configuration, resulting in a female child.
If a sperm carrying a 'Y' chromosome fertilizes the egg, the zygote will have the XY chromosome configuration, resulting in a male child.

Therefore, it is the 'X' or 'Y' chromosome present in the fertilizing sperm that determines the sex of the human embryo.