During development, an XX female embryo will form one of the X chromosomes in each cell into a Barr body. This usually occurs
A) about two weeks after zygote formation.
B) by the end of the first trimester.
C) at the 16-cell stage.
D) in the X that has the most recessive alleles.
A) about two weeks after zygote formation.
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Select all of the following that are characteristics of crustaceans.
_____ two pairs of antennae. _____ antennal glands. _____ maxillary glands ._____ calcium carbonate deposited in the exoskelton. _____ external fertilization.
Which latitude is most likely to have a desert?
a. 30? north and south b. 30? east and west c. 45? north and south d. 50? north and south e. 70? north and south
The planet Mercury is closer to the sun than the planet Venus. However, temperatures on Venus are hotter than temperatures on Mercury. Why would this be the case?
A) Mercury has a thicker atmosphere than Venus that blocks heat from the sun. B) Mercury spins more quickly than Venus, so its surface cannot heat up as quickly. C) Venus has a thicker atmosphere than Mercury that traps heat from the sun. D) Venus is cooled by high concentrations of water vapor in its atmosphere.
The risk of cancer can be reduced by ________
A) avoiding unnecessary medical x-rays B) smoking more because nicotine can kill cancerous cells C) increasing saturated fats in the diet D) decreasing fruit intake because fruits can be carcinogenic