The crossing over mechanism of genetic variation results from the exchange of gene segments between non sister chromatids. The correct answer is A.
Convection currents in magma drive plate tectonics. The answer is true.
The gland that controls formation would be testes.
<span>When you are pregnant, you do not ovulate because you have already fertilized an egg and it is embedded into the uterus where it is growing into a baby. The body knows this, so it does not shed the uterine lining. The shedding of this lining is triggered by hormones which change when the body is pregnant. During pregnancy, a large amount of progesterone is initially produced which helps to prevent the lining from shedding. If you are not pregnant, your progesterone level will begin to decline at the end of your cycle, triggering the shedding of the lining and the period. Birth control pills alter your hormones to mimic a pregnant state. This will prevent the body from releasing an egg and then shedding the uterine lining.</span>
