When a human egg is fertilized by a sperm having 'Y' chromosome, the zygote has the following combination of chromosomes:

As given in the NCERT chapter, human beings have 23 pairs of chromosomes — 22 pairs are the same in both males and females and are called autosomes (44 in number), while the 23rd pair consists of the sex chromosomes, which may be similar (XX) or dissimilar (XY). The mother contributes only X-chromosomes (since she is XX), so every egg carries one X chromosome and $22$ autosomes ($22+X$). The father is XY, so half his sperm carry an X chromosome and half carry a Y chromosome; thus a sperm is either $22+X$ or $22+Y$. As the NCERT text explains, 'a child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy' — the sex of the child is decided by which chromosome (X or Y) is present in the fertilising sperm, since the mother's contribution (X) is fixed.

When the egg ($22+X$) is fertilised by a sperm carrying the Y chromosome ($22+Y$), the resulting zygote receives $22$ autosomal chromosomes from the mother and $22$ autosomal chromosomes from the father, giving $44$ autosomes, together with one X (from mother) and one Y (from father) sex chromosome. Hence the zygote's chromosome combination is $44+XY$, and the child develops as a boy.

Why option C is correct: $44+XY$ correctly shows 44 autosomes (22 from each parent) plus one X (maternal) and one Y (paternal) sex chromosome, exactly the combination produced when a Y-bearing sperm fertilises the egg, as described in the chapter.

Why the distractors are wrong:

• Option A ($44+XX$): This is the chromosome combination of a zygote that will develop into a girl, produced when an X-bearing sperm (not a Y-bearing sperm) fertilises the egg. Since the question specifies fertilisation by a Y-carrying sperm, this combination is incorrect.
• Option B ($22+XX$): This total of only $22$ chromosomes represents a single gamete (an unfertilised egg's autosomal count), not a zygote. A zygote is formed by fusion of egg and sperm and must contain $44$ autosomes (22 from each parent), so this option is numerically inconsistent with a fertilized zygote.
• Option D ($22+XY$): Like option B, this shows only $22$ autosomes, which corresponds to a single gamete (e.g., a Y-bearing sperm, $22+Y$), not the zygote formed after fertilisation. A zygote must have double the autosome number, i.e., $44$, not $22$.