The Smiths have four children, all girls. Their fifth child is a boy. Why did this change occur?
A) the father' contribution of a Y chromosome.
B) the conception classes taken by the parents.
C) the mother' contribution of a Y chromosome.
D) the timing of the fertility cycles.
The answer is A) the father's contribution of a Y chromosome. This change occurred because the father's sperm carries either an X or a Y chromosome, and in this case, the sperm with the Y chromosome fertilized the egg, resulting in the birth of a boy.
The correct answer is A) the father's contribution of a Y chromosome. This change occurred because the father, Mr. Smith, contributes a Y chromosome to the child while the mother, Mrs. Smith, contributes an X chromosome. When a sperm carrying a Y chromosome fertilizes the egg, the resulting child will be a boy. This change in the gender of the child is determined by the combination of chromosomes from both parents during fertilization.
To understand why this change occurred, one needs to have knowledge of human genetics and the process of conception. Understanding the basics of how chromosomes determine the gender of a child is important. In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). During conception, the father's sperm carries either an X or a Y chromosome, while the mother's egg always carries an X chromosome. If a sperm carrying an X chromosome fertilizes the egg, the resulting child will be female. However, if a sperm carrying a Y chromosome fertilizes the egg, the resulting child will be male.
Therefore, the change in the Smiths having four girls and then having a boy occurred because the fifth child received a Y chromosome from the father during fertilization.