AP Biology: Genetics. In desperate need of help

[Marconis]

For the first time in AP Bio, I have hit a massive road block that I just cannot step over. We are up to Genetics (chapter 14 in Campbell/Reece) and I do not get it one bit. I cannot do probability for the life of me, and I am just stressing so much. The textbook didn't teach me anything, along with my teacher who gives bad lectures. Are there any online resources that greatly outline the basics of Genetics (just Mendel and the gene idea). I would love a bunch of visuals that show all the crosses and everything. Thank you so much.

[muhali3]

If you're doing a dihybrid cross you don't need to draw a whole punnett square for probability. Break it up into two monohybrid crosses then multiply the probability of both. You can do this with any size cross.

 

So if you're doing AaBb x AaBb and want to find the prob. of AABB.

 

Do Aa x Aa and find the prob of AA which would be 1/4.

 

Do Bb x Bb and find the prob of BB which would be 1/4.

 

Multiply the probabilities. 1/4 x 1/4 = 1/16 prob of AABB.

 

Here's what it looks like visually but you don't need to draw it out because it takes much longer. http://updatecenter.britannica.com/eb/image?binaryId=775&rendTypeId=4

 

This is a simple monohybrid cross, even though I assume you already know. http://media-2.web.britannica.com/eb-media/74/774-004-DFEB8A50.gif

 

All you really need to know is that a gene is inherited and codes for a protein, which could be responsible for hair color, eye color, and other phenotypes. Each individual can only have two alleles (variants) of a single gene. So if hair color is a single gene, the alleles for it would be black, blue, blonde, brown etc. But one person can only have two alleles, for example black and brown.

 

There isn't much genetics on the AP Bio test. It's won't be hard if this is the only thing you've had trouble with. I got a 5 on it and didn't stress myself too much over anything.

Edited November 14, 2008 by muhali3