According to the play Twelve Angry Men, what are the factors which can influence a jury's decision-making process (including minority influence)? How realistic is the play?

In the play Twelve Angry Men, readers discover that there has been a murder. At the start of act one, the case has been presented and the judge reiterates the charge against a nineteen-year-old boy:

"Murder in the first degree—premeditated homicide—is the most serious charge tried in our criminal courts. You’ve heard a long and complex case, gentlemen, and it is now your duty to sit down to try and separate the facts from the fancy. One man is dead. The life of another is at stake."

In this statement, the judge reminds the jurors of a few important things. Firstly, he reminds them that someone has already died. The accused boy may be put to death if he is convicted of murder. The judge reminds the jurors that their decision holds the power of life and death. A bit later, the judge also reminds them that their decision must be unanimous: everyone has to agree.
At first, the men decide to vote, wondering if they might all agree from the start. They cast their votes and find that only one man has any doubt of the boy's guilt. If this man, with some doubt, had voted that the boy was guilty, the boy likely would have received the death penalty. Because juror eight had some doubt, he decided to delay and force the men talk more about the case before they made their final decision. This frustrates many of the men who think the verdict is obvious.
In act 1, juror number three and juror number eight discuss the case:

THREE. I never saw a guiltier man in my life. You sat right in court and heard the same thing I did. The man’s a dangerous killer. You could see it.
EIGHT. He’s nineteen years old.
THREE. That’s old enough. He knifed his own father. Four inches into the chest. An innocent nineteen-year-old kid. They proved it a dozen different ways. Do you want me to list them?

From this quote, you can see that the teenager is judged by his appearance. Juror three uses the evidence that you could "see" that the boy was a "dangerous killer." Additionally, he is judged for his socioeconomic background. Juror seven and eight talk together:

SEVEN. . . . I think the guy’s guilty. You couldn’t change my mind if you talked for a hundred years.
EIGHT. I don’t want to change your mind. I just want to talk for a while. Look, this boy’s been kicked around all his life. You know, living in a slum, his mother dead since he was nine. That’s not a very good head start. He’s a tough, angry kid. You know why slum kids get that way? Because we knock ‘em on the head once a day, every day . . .

Here, we see that the men have judged the teenager because he is from the slums. He's deemed a "tough, angry kid" because he lives in the poor area of the city. It is likely that this teenager from the slums was from a minority group. Two factors that influenced the jurors' initial decision included the socioeconomic background and the physical appearance of the accused teenage boy.