Occasionally a child is born with an extra chromosome 13, but never do you see a child with an extra chromosome 12, why?

This is because some of the trisomies (one extra chromosome, three instead of two) are fatal, births cannot survive.

Theoretically, trisomies can occur with any chromosome, but often result in miscarriage.

The types of autosomal trisomy that survive to birth in humans are:

Trisomy 8 or Warkany syndrome 2

Trisomy 9

Trisomy 13 or Patau syndrome

Trisomy 18 or Edwards syndrom

Trisomy 21 or Down syndrome.

the right answer is a. skin cells forming from sunlight.

the liver is an organ endowed with a fantastic ability to regenerate

. thus, if a hepatectomy (ablation) of 70% of the hepatic mass is performed in the rat, there is complete recovery in 7 to 10 days.

prokaryotes are beings that have existed since the existence of life on earth, and do not come from another realm.

ribosomes are organelles that exist naturally in eukaryotes, either in free form or attached to the endoplasmic reticulum.

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4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."