Recessive<span> and </span>dominant alleles<span>. You will recall that genes have </span>different<span> forms called </span>alleles<span>. An </span>allele<span> can be </span>recessive<span> or </span>dominant<span>. A </span>recessive allele<span> only shows if the individual has two copies of the </span>recessive allele<span>.</span>
This question is very good
<u>Answer:-</u> <em>Option C </em>- evidence that microorganisms cannot grow in boiled broth when new organisms were not allowed to enter.
<u>Explanation:-</u>
- <em>Theory of spontaneous generation</em> stated that the living organisms can be created from non living matter. However, this theory was disapproved and replaced by the <em>cell theory</em> which stated that all living organisms are created from cells and new cells arise from pre-existing cells.
- There were several experiments conducted by various scientists to disapprove the theory of spontaneous generation however, the experiment that was most successful to do so was the one conducted by <em>Louis Pasteur</em> in 1859.
- <em><u>Description of the experiment:-</u></em>
-In his experiment, Pasteur boiled a meat broth in a flask (it was known that boiling the broth kills the micro organisms) and then heated the neck of the flask to bend into a S- shape.
The purpose of the S shaped neck was to allow the air to enter into the flask but not the micro-organisms as the micro organisms will settle by gravity in the neck and not reach into the flask.
<em>observations of the experiment</em> :-
1. Pasteur observed that even though the air entered the flask no micro organisms were growing in the flask.
2. Further,when he tilted the flask so that the broth came in contact with the part of the neck where the air borne microorganisms could have settled he was able to observe microbial growth in the flask.
These observations laid the theory of spontaneous generation to rest and proved that <em>organisms can only grow in the presence of pre-existing cells </em>which in this case were the microorganisms.
