Answer:
The base pairing of complementary regions of RNA leader sequence determines if the transcription will be attenuated at the end of leader sequence or will continue for structural genes.
Explanation:
The RNA leader sequence of trp operon is the site where the transcription is initiated.
When tryptophan levels are high, translation of sequence 1 of the leader sequence is followed by base pairing between the complementary 3 and 4 regions of the leader sequence. The base pairing forms a terminator like attenuator and stops the expression of structural genes.
When tryptophan is not present, ribosome pauses at tryptophan codon of region 1 of the leader sequence. Hence, the regions 2 and 3 of the leader sequence base pair and prevents the formation of attenuator by not allowing the region 3 to pair with region 4.
Answer:
Temperatures in a desert climate range from 86 to 104 degrees Fahrenheit, while summers are wet and winters are dry. When the rains fall, herds of prey animals abound as they feed on the lush grasslands and water at the many waterholes and rivers. The average rainfall in the desert is 10 inches per year. Sahara desert vegetation includes African Welwitchsia, date palm, thyme, magaria, olive trees, orange trees, and fig trees. Apart from these, more than half of the Sahara desert is extremely barren with no vegetation found. However, there are still some areas in the Sahara desert that are lush, containing abundant trees and plants. The most common landscape features found in deserts are sand dunes, yardangs, desert pavements, debris, playas, oases, mesas, alluvial fans, arroyos and buttes. These landforms vary from desert to desert. In areas dominated by the tundra climate type, winters are long and cold, especially in the region north of the Artic Circle where, for at least one day in the year, the Sun does not rise. Winter precipitation generally consists of dry snow, with seasonal totals less than in the summer when cyclonic storms that develop along the boundary between the open ocean and sea ice yield rainfall. The average snowfall in the tundra is 10-40 inches per year. Tundra vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone between the tundra and the forest is known as the tree line or timberline. The arctic tundras located between the north pole and the coniferous forests or taigaregion. It is characterized by extremely cold temperatures and land that remains frozen year-round. Arctic tundra occurs in frigid mountaintop regions at very high elevations.
Answer:
The correct option is <em>A. convergent evolution</em>
Explanation:
The phenomenon of evolution explains how different species might have common ancestors. This phenomenon explains that genetic variations might have led to the birth of different species from a common ancestor.
Convergent evolution can be described as a type of evolution in which similar features or traits can be observed in organisms although they may not have any genetic sequence in common. For example, sharks and dolphins look similar but they have huge differences in their genomes.
Because freezing will often burst the cell walls and destroy tissue. The crystals of ice are very sharp and hard to control AFAIK. Note what happens to a banana or many types of fruit after you dethaw — it becomes all mushy and not of the same structure, fiber and cell form as before, like a bad beam up in Star Trek.
While mitosis produces 2 daughter cells from each parent cell, meiosis results in 4 sex cells, or gametes in males and 1 in females. Unlike the cells created by mitosis, gametes are not identical to the parent cells. In males, meiosis is referred to as spermatogenesis because sperm cells are produced.
