Alright, so I need two questions answered. I already did that, but I'd like to check if I got anything wrong:
1. On a family pedigree tree, how can you tell if a trait is caused by a recessive allele?
2. On a family pedigree tree, how can you tell if a trait is caused by a dominant allele?

My answers:
1. In order for a recessive trait to show you must have two identical recessive alleles. So if two parents with the same trait were always having children with the same trait, then the trait being examined could be recessive. It may also not be recessive but homozygous dominant, so you must look at multiple individuals of a family tree.
2. In order for a dominant trait to show you must have at least one dominant allele (the other one doesn't matter - could be heterozygous, or homozygous dominant - the same dominant trait will still show). The easiest way to tell apart a dominant trait is to look at two parents who have the same phenotype, and if their children are not all the same, then the trait is dominant. The genotypes of both the parents might also be homozygous dominant and in that case, the children will still all have the same trait, so you must look at multiple individuals of a family tree in order to ascertain if a trait is dominant.

fuck, this is so hard to explain, but i have the knowledge. anyone have better ways of explaining this?
this has nothing to do with sex-linkage btw

This post was edited by voniazmogis on May 19 2013 04:18am

Just remember that recessive it needs both alleles for the recessive phenotype to show, so it is very likely that it will skip generations. Like in the recessive case if both parents show the recessive phenotype you know that all their kids are going to also have both recessive alleles, but if like say the dad is xx and the mom is Xx then you have a 1/2 chance that the kid wont have it, however he is still a carrier type deal.

I just realized after trying to explain this that it is indeed very hard to type out:P

Here is a picture of a recessive pedigree.




take notice to the skipping of generations.


Dominant on the other hand you only need one of the alleles genotypically(is this a word?) to give the apparent phenotype. So even if both parents have the dominant phenotype, if they are both Xx then it is possible that their kids will not have the disease. It is also important to note that if two people who do not show the phenotype in the case of autosomal dominant have children, there is absolutely NOOOOO way that their kids could have the disease.

Here is a picture of a dominant example




I just woke up and my brain is not functioning yet so if you still do not understand say something and I will help you out as much as I can, If you have any other questions about genetics/genomcis/molecular bio/biochem, and actually want to learn(as in you don't just want me to do your homework), I will be happy to help with anything.

LOL my pictures suck sorry

I think I understand it now. I have spent hours trying to explain it in my paper in excruciating detail. Hopefully I do good (which I should). Thanks