How are new alleles created? Occasionally, DNA mutations occur in germ cells – cells destined to become eggs or sperm. In this case, the DNA mutation is copied into every new cell of the growing embryo following fertilisation. ... If the mutation affects a gene, it will result in a new version of that gene – a new allele.
Answer: A: Its fertile oases enabled farmers to grow enough food for themselves and for sale.
Explanation: The Arabia region is a region located within the Arabian desert. A desert is an area of extreme heat, often dry weather condition with barren lands that cannot support agriculture and food production. An oases on the other hand is a region of luscious, cultivate-able land within a desert.
Food is one of the most important basic needs of man and hardly can anyone survive without food for more than twenty days. Hence, the presence of oases within the otherwise dry environment of the Arabia region is a major protection against death from hunger.
Taking a closer look at other options, none of them guarantees food supply and income to the Arabia region unlike food production in oases. Hence, the fertile oases is really the most important factor that serves as protection in the region's history.
Correct option: A
The extracellular glucose inhibit transcription of the lac operon (D) by reducing the levels of intracellular cAMP.
Lac operon is the assembly of various genes that are involved in the uptake and metabolism of lactose of E. coli or any other bacteria. It consists of a regulator gene, promoter gene, operator and structural gene. Structural genes are three: z, y and a. Each codes for a different enzyme.
cAMP is the cyclic Adenosine Monophosphate. It is produced by the bacteria when there are low levels of glucose in it. Hence it is also named as hunger signals. Therefore, cAMP is responsible for activating the operon to produce lactose.
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