It is clear that throughout the novella Kino changes greatly thanks to the introduction of the pearl into his life. He starts off as your average hard-working Mexican fisherman, desperately trying to provide for his wife and son and battling against poverty and discrimination to succeed in this goal.

However, with the advent of the pearl into their lives, which should have been a blessing, it is clear that evil only comes. The pearl's malign influence distorts Kino's perceptions of reality and causes him to become absolutely fixated on getting the right price for the pearl so that he can allow his son to break out of the poverty trap that has dominated these lives. Pursuing this goal, however, causes him to change. Note what he says to his wife when she insists that the pearl is evil:

And as she spoke the light came back in Kino's eyes so that they glowed fiercely and his muscles hardened and his will hardened.

His face becomes "crafty" when he thinks of what he must do to sell the pearl. In the next chapter, when Juana tries to dispose of the pearl, he hisses at her "like a snake" with bared teeth, hitting her. However, perhaps most chillingly, in spite of all of these transformations, is what Kino says at the end of chapter five:

"This pearl has become my soul," said Kino. "If I give it up I shall lose my soul."

We see here the way that Kino's life has become completely dominated and obsessed with the pearl. He links it inextricably to his soul, indicating the malign influence that the pearl is having on him. Of course, with such an influence, only a tragedy is able to break it, and the death of his son gives Kino the strength he needs to return the pearl to the sea from whence it emerged.

Compare and contrast the relationship between Kino and Juana at the beginning and the end of The Pearl.

At the beginning of The Pearl, Juana and Kino seem to have a close relationship.  He describes her as in some ways tougher than himself.

Kino had wondered often at the iron in his patient, fragile wife. She, who was obedient and respectful and cheerful and patient, could bear physical pain with hardly a cry. She could stand fatigue and hunger almost better than Kino himself. (ch 1, p. 4)

Kino acts helpless, but it is Juana who sucks the scorpion venom from the baby’s wound and asks for the doctor.

At the end of the story, Kino and Juana are only somewhat changed by their experiences with the pearl and the baby’s death.  Juana seems more changed than Kino.

Her face was hard and lined and leathery with fatigue and with the tightness with which she fought fatigue. And her wide eyes stared inward on herself. She was as remote and as removed as Heaven. (ch 6, p. 47)

The disagreement over the pearl and the death of the baby has been a blow to their relationship.  Yet despite this, Juana and Kino remain together.  When they stand side by side, they do so both physically and metaphorically.  Kino’s family song rises again, and they are ready to go on with their lives.

How does Juana and Kino's relationship change throughout The Pearl?

Juana is a dutiful wife. She is religious. She defers to her husband's judgment. It is her prayers, they believe, that have allowed Kino to find the pearl in the first place. However, after they find the pearl, their son survives the scorpion bite, and Juana begins to see that Kino has become obsessed with the pearl and what it can get him in life - not only money, but prestige. She begins to see the pearl for what is - something that her husband has made into an idol. Although she still respects him and acknowledges his leadership in the family, she begins to beg him to get rid of the pearl. She begins to see it as something evil. She sees that it has become more important to him than his family. She even goes so far as to try to get rid of it, which, even though she fails in her attempt, represents a big change for her because in the beginning of the story, she would not have even considered defying her husband.

Read about it here on eNotes.