out come of directional selection....pl REPLY ASAP

[kandarp shah]

guys,
this is the the question that i am having toruble explaning...please help.
Here's is my question and educated guess.

1)As long-term studies show, prospects for human newborns of very high or very low birth weight are not good. Being born too small increases the risk of stillbirth and early infant death. Is this an outcome of directional, disruptive, or stabilizing selection? Explain your response.
ANS:Babies that have very high or low birth weights is an example of
diversifying selection, caused by the increased use of fertility drugs and
the excellent medical care that modern hospitals are able to provide to
newborns, which saves babies who would die otherwise and allows them to
pass on their “weak” genes to the next generation.

[2810712]

... which is the trait that u r refering to. is it wt or goodness [ or -ve badness] of a specefic wt. weight or av. goodness of wt ...



How can for the trait to be wt. the maxima should lie somewhere in the middle , so this can't be the diversifying selection. Even if the high wt children and low wt. children are equal in no. to av. wt. having children
this doesn't form a resultant of diversifying selection.

If we plot badness on Y-ax. and wt. on X ax. We get two maxima... this resembles the resultant of diversifying selection.

The line that has that 'weak' gene, can be said weak only in this context [for this trait] that too as they are dependent on those 'artificial' facilities.
Still i think there would be selection of average wt. as we can't say that adequate facilities are available whenever required.. but it would be tooooooo slow. and their contribution to popullation will aproach zero but never become zero [ as efficiency of these medical aids in changing as research is going on and it also depends upon how many people require it. If the no. of less wt. or high wt. children becomes lesser the efficiency [ the no. of such weak children surviving till they repro. ] increases.

Hope that the badness of this post is negative...

Shrei