Independent Assortment & Crossing Over: Genetic Recombination

[tica86]

1. When crossing over does not occur, how many possible chromosome combination can result from independent assortment of the homologous chromosomes?
I believe it is 4, because we have 4 identical chromosomes. Is this correct?

2. How does this change when crossing over occurs? It increases or decreases the genetic recombination? I believe it increases the genetic recombination but I'm not sure.

I would appreciate any help, thanks!

 

[physicsguy101]

2. How does this change when crossing over occurs? It increases or decreases the genetic recombination? I believe it increases the genetic recombination but I'm not sure.

You're correct on that. Crossing over yields an enormous possibility for genetic recombination and therefore variation.With regard for question #1, I'm a bit confused as to what exactly it is asking. Even without crossing over, there is still a great number of ways homologous chromosomes can line up. In the human gamete during meiosis, there are 23 tetrads lining the metaphase plate during Metaphase 1. These can line up in any order, and the one on each pole of the plate being different from the other order creates a huge possibility even without crossing over. I'm not sure what the question is looking for, though watch your vocabulary when discussing "identical" chromosomes. Since one of the two alleles for a specific trait is from each parent, they are not always identical. They have the same size and code for similar proteins, though their genetic nucleic acid makeup differs slightly (i.e. blue eyes vs brown eyes, etc.).

I hope that helps!