Answer:
Tetraploid wheat evolved by allopolyploidization and subsequent diploid-like behavior due to cytological diploidization
Explanation:
Durum wheat (<em>Triticum durum</em>) or pasta wheat, is a tetraploid wheat species that has 28 chromosomes, i.e., seven pairs in each genome (2n = 4x = 28). Durum wheat was domesticated from wild emmer wheat, which originated by hybridization of two diploid wheat species with 14 chromosomes: <em>Triticum monococcum</em> (genome AA) and one wild progenitor (genome BB). <em>Triticum durum </em>is a typical example of evolution by hybridization and polyploidization, where the resultant tetraploid species has two complete sets of chromosomes. Allopolyploidization is one of the most common types of plant speciation. During meiosis, 28 chromosomes form 14 homologous chromosome pairs, because homologous chromosomes have developed 'restriction of pairing' (i.e., cytological diploidization). The restriction of pairing to fully homologous chromosomes ensures a correct meiotic behavior, which otherwise would be altered due to the high level of homology that still exists among chromosomes from different wheat progenitors.
The hormone testosterone promotes sexual desires in both males and females
Hello! Autotrophs make their own food (plants) and heterotrophs consume other organisms for energy (consumers.) Autotrophs use the process of photosynthesis to produce the oxygen as one of its products. Heterotrophs use the oxygen produced by the autotrophs to perform cellular respiration, which releases carbon dioxide that plants use; it's a balanced cycle. Hope this helps!
Answer:
1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
Explanation:
Stabilizing Selection
This type of natural selection occurs when there are selective pressures working against two extremes of a trait and therefore the intermediate or “middle” trait is selected for. If we look at a distribution of traits in the population, it is noticeable that a standard distribution is followed:
Example: For a plant, the plants that are very tall are exposed to more wind and are at risk of being blown over. The plants that are very short fail to get enough sunlight to prosper. Therefore, the plants that are a middle height between the two get both enough sunlight and protection from the wind.
Directional Selection
This type of natural selection occurs when selective pressures are working in favour of one extreme of a trait. Therefore when looking at a distribution of traits in a population, a graph tends to lean more to one side:
Example: Giraffes with the longest necks are able to reach more leaves to each. Selective pressures will work in the advantage of the longer neck giraffes and therefore the distribution of the trait within the population will shift towards the longer neck trait.
Disruptive Selection
This type of natural selection occurs when selective pressures are working in favour of the two extremes and against the intermediate trait. This type of selection is not as common. When looking at a trait distribution, there are two higher peaks on both ends with a minimum in the middle as such:
Example: An area that has black, white and grey bunnies contains both black and white rocks. Both the traits for white and black will be favored by natural selection since they both prove useful for camouflage. The intermediate trait of grey does not prove as useful and therefore selective pressures act against the trait.
