Answer:
Selection is a directional process that leads to an increase or a decrease in the frequency of genes or genotypes. Selection is the process that increases the frequencies of plant resistance alleles in natural ecosystems through coevolution, and it is the process that increases the frequencies of virulence alleles in agricultural ecosystems during boom and bust cycles.
Selection occurs in response to a specific environmental factor. It is a central topic of population and evolutionary biology. The consequence of natural selection on the genetic structure and evolution of organisms is complicated. Natural selection can decrease the genetic variation in populations of organisms by selecting for or against a specific gene or gene combination (leading to directional selection). It can increase the genetic variation in populations by selecting for or against several genes or gene combinations (leading to disruptive selection or balancing selection). Natural selection might lead to speciation through the accumulation of adaptive genetic differences among reproductively isolated populations. Selection can also prevent speciation by homogenizing the population genetic structure across all locations.
Selection in plant pathology is mainly considered in the framework of gene-for-gene coevolution. Plant pathologists often think in terms of Van der Plank and his concept of "stabilizing selection" that would operate against pathogen strains with unnecessary virulence. As we will see shortly, Van der Plank used the wrong term, as he was actually referring to directional selection against unneeded virulence alleles.
Answer:
B
Explanation:
B is the most likely consequence because of the following facts we are told:
- After apple trees were introduced, some apple maggots began feeding from and laying their eggs on apple trees
- Adult apple maggots will only mate on the type of tree on which they were born.
This provides a geographical isolation (because they are feeding and laying eggs on separate trees) and reproductive isolation (because they will only mate on the type of tree on which they are born).
These two factors increase the chances that apple maggots feeding on apple trees will only encounter those who have mated on the same tree, and continue to mate this way. Over time, the populations (i.e. apple tree vs hawthorn tree) will intermix less and less. This will mean the genetic pool will become distinct, and natural selection will be acting differently (different habitats and different genes), encouraging speciation.
No estoy seguro que decir, pero sí es difícil
Answer:
Dominant
Explanation:
A hybrid trait is also known as heterozygous, which is the combination of the dominant and recessive alleles of a gene. On the other hand, a purebred is combination of the same two dominant alleles or the same two recessive alleles. For example, in the gene coding for height, allele for tallness (T) is dominant over the allele for shortness (t).
A purebred for this trait will either be "TT" or "tt" while a heterozygous or hybrid will be Tt. Hence, according to this question, crossing of a hybrid (Tt) and a dominant purebred (TT) will always result in offspring which are DOMINANT (see attached image).
Answer:
<h2>e) 3/4
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Explanation:
As given;
Black (B) is dominant over red (b), so B is dominant over b.
Solid (S) is dominant over spotted color(s), so S is dominant over s.
Offspring of BBss and bbss individuals are:
Gametes of parent BBss are Bs, Bs and gamete of bbss are bs, bs
offspring are : all Bbss
Cross between these offspring is; Bbss×Bbss
Gametes of parent Bbss are: Bs and bs as given that the genes are linked.
Bs, bs × Bb, bs
Offspring are = BBss, Bbss, Bbss, bbss
Black spotted (B_ss) = 3/4
