Sarah Milewicz, Blog 3, Tuesday April 20, 2010, 3/3

What we did in Class

• Wrote our Mitosis & Meiosis Unit Exam

Thoughts About the Material

• We just learned about Punnet Squares and they are pretty easy to use when looking for what kind off offspring two certain organisms breed.  I think they're really useful and I thought it was cool that for Mendel's F1 generation for a monohybrid cross there was always a 3:1 ratio for the offspring and for a dihybrid cross it was always 9:3:3:1.  It's interesting that he actually took the time to figure those things out (his life must have been pretty boring). 

Above and Beyond

• In class today (April 22) we learned about lethal alleles and i was wondering how they actually occurred in the first place.  I went the the website http://en.wikipedia.org/wiki/Lethal_alleles but i didn't find out why they occurred.  I did find out that most lethal genes are recessive and recessive lethal alleles don't cause death in the heterozygous form because a certain threshold of protein output is maintained. In the homozygous form, the protein output doesn't meet that threshold and because of that, the organism dies.  I found some other examples of lethal alleles and they are cystic fibrosis and brachydactyly.  Cystic fibrosis is referred as the characteristic scarring and cyst formation within the pancreas, which causes progressive disability and often early death.  Brachydactyly literally means "shortening of the fingers and toes."  The shortness is related to the length of other long bones and other parts of the body.