Choose one correct option A, B, C, or D that best completes each of the numbered spaces in the text.

We all know that we inherit physical characteristics and personality traits from our parents. But
how does it work? If three children all have the same ----31----, how can they be so different? Why
don’t they inherit the same characteristics? Depending on how much you have already learnt about
genes and ----32----, you will find it an easy or difficult question to answer in detail. There are
twenty-three pairs of ----33---- in the nucleus of each cell in the human body, which means we have
----34---- in total. In each pair, one chromosome comes from our ----35---- and one from our father.
In reproduction, the male and the ----36---- both manufacture special reproductive cells called
gametes (sperm and ----37---- respectively), which contain only twenty-three chromosomes instead
of the normal forty-six. These twenty-three consist of material from both the “mother chromosome”
and the “father ones”. So, when the ----38---- meets the egg and fertilizes it, the new cell has the full
number of forty-six chromosomes again, and there is genetic ----39---- from the man’s mother and
father, and from the woman’s mother and father. And each time reproduction occurs, the mixture is
different. This is why a couple’s ----40---- are all equal.