The mechanisms of reproductive isolation prevent the reproduction of two individuals from different species. The prezygotic mechanisms disrupt the stages of reproduction before the forming of the zygote or prevent the mating at the start, and the postzygotic mechanisms affect the stages of reproduction after the forming of the zygote.
So, the first and the third example (the urchins and the grasshoppers) show the prezygotic mechanism, as the two individuals are not able to mate or form a zygote.
The second and the fourth example ( zonkey and the death of a zygote) show the working of the postzygotic mechanisms, as the zygote is formed, but it seems to be inviable, and the zonkeys are sterile, preventing the individual to reproduce.
Many scientists are concerned that the Ogallala aquifer in the United States is being depleted at an alarming rate. The statement that is correct and would state the most likely be a major effect of this aquifer running dry is choice A. It states that many crops would die because irrigation water would be limited.
Answer: The correct answer would be option a.
Explanation:
The hemoglobin in red blood cell has a tendency to bind to oxygen as well carbon dioxide in a reversible manner. It depends upon the partial pressure of the gas.
For example, at tissue site, the concentration of carbon dioxide is higher than oxygen due to which the affinity of hemoglobin increases for carbon dioxide.
In hemoglobin, carbon dioxide reacts with water to form bicarbonate ions and hydrogen ions.
At alveolar site, these ions again convert into carbon dioxide and excrete out of the blood as a part of exhale air.
The randomness in the alignment of recombined chromosomes at the metaphase plate, coupled with the crossing over events between nonsister chromatids, are responsible for much of the genetic variation in the offspring. To clarify this further, remember that the homologous chromosomes of a sexually reproducing organism are originally inherited as two separate sets, one from each parent. Using humans as an example, one set of 23 chromosomes is present in the egg donated by the mother. The father provides the other set of 23 chromosomes in the sperm that fertilizes the egg. Every cell of the multicellular offspring has copies of the original two sets of homologous chromosomes. In prophase I of meiosis, the homologous chromosomes form the tetrads. In metaphase I, these pairs line up at the midway point between the two poles of the cell to form the metaphase plate. Because there is an equal chance that a microtubule fiber will encounter a maternally or paternally inherited chromosome, the arrangement of the tetrads at the metaphase plate is random. Thus, any maternally inherited chromosome may face either pole. Likewise, any paternally inherited chromosome may also face either pole. The orientation of each tetrad is independent of the orientation of the other 22 tetrads.
Explanation:
A hormone is a molecule that functions as a chemical signal. A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Endocrine hormone molecules are secreted (released) directly into the bloodstream. !
