The precambrian era makes up about 90% of the earths history, but there was little to no living organisms at the time other than microscopic ones. The first eukaryotes were found in the cambrian period after the precambrian period, not only that but at the end of the precambrian era in the Proterozoic era there was a mass extinction of about 70-80% of all living organisms
Answer:
The dihybrid ratio we expect in the offspring is 9:7.
Explanation:
This is an example of complementary gene interaction, which is the non allelic interaction or genes, where the prominent genes at heterozygous loci may complement each other by complementing recessive alleles at the respective loci.
So in this case of complementary gene interaction, the individuals that are A-bb or aaB- or aabb will have the same set of observable features (phenotype) but only A-B- individuals will how the dominant phenotype.
Floods (when it rains a lot, rivers tend to keep rising which leads to flooding )
Answer: meiosis creates new combinations of genetic material in each of the four daughter cells. These new combinations result from the exchange of DNA between paired chromosomes. Such exchange means that the gametes produced through meiosis exhibit an amazing range of genetic variation.
Explanation:
Answer: A
Explanation:The Trp operon is responsible for synthesis of the amino acid trytophan when it is not available in the cellular environment.
When the tryptophan is plentiful, a repressor protein binds to two molecules of tryptophan.
Thiss repressor-tryptophan complex binds to the trp operator. This binding prevents the binding of RNA polymerase, so the operon is not transcribed, and no new trptophan is produce.
On the other hand, when tryptophan levels are reduced, the inactive repressor will not bind the tryptophan operator so the operon is transcribed.
Regulation of the trp operon is determined by the concentration of tryptophan; when adequate tryptophan is present in the growth medium, there is no need for tryptophan biosynthesis.
Transcription is turned off when a high concentration of tryptophan is present, and is turned on when tryptophan is absent. The regulatory signal is the concentration of tryptophan itself.
Therefore in the absence of tryptophan, the inactive repressor cannot bind trpO, so operon gene transcription occurs.
