All female mammals have one active x chromosome per cell instead of two. what causes this? a) activation of the xist gene on the x chromosome that will become the barr bodyb) activation of the barr gene on one x chromosome, which then becomes inactivec) inactivation of the xist gene on the x chromosome derived from the male parentd) attachment of methyl (ch3) groups to the x chromosome that will remain active

The answer is; A

XIST RNA is a significant gene on the X chromosome (long (q) arm) that is involved in its inactivation in females, who have two X chromosomes. XIST RNA gene is activated in one of the X chromosomes, inactivating this chromosome and forming a Barr body.  

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.