Stem cells are undifferentiated cells that could develop to perform a variety of tasks. One type of stem cell is the embrionic stem cell. There are also adult stem cells. To use embrionic stem cell you need to have fertilized embrios. These can be donated to research. The use of the embrionic stem cells is controversial for this reason.
Answer:
the third option, commensalism
Explanation:
The Precambrian era envelopes the major bulk of the history of the Earth, beginning from the creation of the planet approx 4.5 billion years ago and terminating with the origination of composite, multicelled forms of life approximately 4 billion years after.
The Precambrian refers to the earliest of the geologic ages that are signified by the distinct layers of sedimentary rock. The Earth was about more than six hundred million years old when life started. The planet had cooled down from its native molten state, creating a solid crust and oceans formed by water vapor in the atmosphere.
At about three billion years ago, the atmosphere of the Earth was virtually devoid of oxygen. At approximately 2.4 billion years ago, oxygen was discharged from the seas as a waste product of photosynthesis by cyanobacteria. The levels of the gas slowly raised, attaining about 1 percent around two billion years ago.
Approximately 800 million years ago, the levels of oxygen attained about 21 percent and started to breathe life into more composite species. The oxygen-rich ozone layer was also created, protecting the surface of the Earth from the harmful solar radiation.
Answer:
The most common interaction between alleles is a dominant/recessive relationship. An allele of a gene is said to be dominant when it effectively overrules the other (recessive) allele. Eye colour and blood groups are both examples of dominant/recessive gene relationships.
The main difference between dominant and recessive trait is that dominant genes always passes the dominant behavior genes while the recessive ones pass the recessive behavior genes. In fact, the dominant genes are said to be more likely to pass to future generations, while the recessive ones are less likely to do that.
Explanation:
