Question 1
Which characteristics determine gender (consider genetic, anatomical, hormonal, and other factors)? Is it always the case that genetic, psychological, and physical gender cues indicate the same gender? Explain your answer, citing specific examples of conditions in which gender does not match sex.Question 2
Describe the events that must occur in order for sperm to penetrate an egg. What prevents more than one sperm from entering? In the case of twins, how many sperm entered the egg? Why must a man have millions of sperm in a semen sample to be considered fertile? If only one sperm were present in the semen and that sperm managed to find its way to the egg, could it fertilize the egg? Explain.Answer 1
Gender is determined by sex chromosomes, by internal and external genitals, by sex hormones, and by psychological factors. Pseudohermaphrodites are XY with male internal genitals, but are deficient in one of the male hormones that trigger formation of external genitals. Thus, they are born looking like girls. At puberty, however, more male characteristics begin to develop. Testicular-feminized males lack androgen receptors so their testes fail to descend and their brains are not masculinized, and their outward appearance is female, though they are sterile. Adrenal tumors can secrete hormones that masculinize or feminize the opposite genetic sex. Sometimes psychological gender identity fails to match genetic sex, for unknown reasons.Answer 2
The sperm must penetrate the corona radiata and the zona pellucida, which surround the egg, in order to get to its membrane. The acrosome of the sperm contains enzymes that disrupt these barriers. The first sperm to reach the membrane binds to a receptor, the sperm and egg membranes fuse, and the sperm nucleus enters the egg. The cortical reaction ensues, in which granules in the egg spill their contents out of the membrane, which alters it in a way preventing additional sperm from binding. Twins result from normal fertilization, but either two eggs are present or the early embryo splits. Only about 100 sperm manage to find the egg, with the other millions swimming off in the wrong direction. One sperm probably does not contain enough enzymes to allow penetration of the egg barriers.