Ans.
Sickle-cell disorder is a genetic disorder, which shows defected red blood cells, due to mutation in the genes for hemoglobin protein.
Malaria is common in sub-Saharan Africa region and there, natural selection favored gene for sickle cells, because it might be beneficial to people having sickle cell disease that makes them able to survive in such condition and transmit their genes to offspring.
On the other hand, in those Africans, who moved to United States, where malaria is uncommon or absent, natural selection favored normal, wild type genes, resulting in fewer people with defected sickle cell.
Hence, sub-Saharan African population shows higher percentage of mutated gene for sickle cell as compared to population of United States.
Thus, the evolutionary process behind this difference is 'natural selection.'
Answer:
When AraC binds to arabinose to initiate the process of transcription, then AraC is acting as an Activator.
Explanation:
Transcription is a process that help to produce messenger RNA from the DNA that is present in the nuceloids of bacteria cells. The production of these mRNA however, depends on the intracellular condition of the bacteria, for example, if there is a need for the protein coded for by the segment or not. In the case of this bacterium, the AraC can act as a repressor only when there is no arabinose sugar in the cell. In the scenario above, AraC will act as an activator because of the presence of the sugar arabinose.
B) Billowy sheep-like clouds.
Answer:
The incorrect statement is that the neural reflex arc becomes slow by the hormones involved.
Explanation:
A neural pathway that controls a reflex is known as a reflex arc. In a reflex arc, the sensory neuron transmits a signal to the interneuron and stimulates it. The interneuron then transmits or passes the signal to the next neuron, that is, a motor neuron. The motor neuron associates with the interneurons in the spinal cord, which transmits messages from the CNS to the body. Thus, a reflex arc comprises the elements, that is, the receptor, integrating center, and the effector. Their main activity is to protect the body from external events.
