Week 11 Notes
Week 11 Notes BSC 114
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This 2 page Class Notes was uploaded by Rebecca Sharp on Saturday April 23, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Stevan Marcus in Winter 2016. Since its upload, it has received 11 views. For similar materials see Principles Of Biology I in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 04/23/16
o For Reviewing Purposes The Law of Segregation says that the two alleles for each gene segregate during gamete formation The Law of Independent Assortment says that the alleles of genes on nonhomologous chromosomes assort independently during gamete formation Environment can also effect phenotypes. For example, hydrangea plants are blue in acidic dirt and pink in neutral dirt. This is called the norm of reaction, the phenotypical range of environmental influence And Genetics Advances Onwards! In the early 1900s, people finally got with the program and realized that genes are really located on chromosomes. o The Chromosomal Theory of Inheritance says that Mendel’s genes have specific loci in the chromosomes and that chromosomes undergo segregation and independent assortment during meiosis. Thomas Hunter Morgan is accredited with being the father of modern genetics for the work he did with fruit flies. o He had the first solid evidence for associating a specific gene with a specific chromosome. It was that eye color was sex linked in fruit flies With sex linked stuff, it’s almost always a variation in the X component, which is why sex linked disorders tend to show up more in dudes. Ladies have 2 Xs, which means 2 chances to get a fully functional working X. Because guys only get 1, it shows up more often. For example, color blindness and hemophilia and muscular dystrophy are all X linked. All you need is 1 uninfected X to avoid these. Guys only get that 1 shot. There are a few that are Y linked, like infertility and Swyer Syndrome. While we’re on the subject of sex differences, in female mammals, one of the X chromosomes in each cell is randomly squished and compressed into something called a Barr Body. This is so that males and females stay balanced in regards to gene expression. If a female is heterozygous in X characteristics, she expresses all of it together, an expression called ‘mosaic’. This is why cats get really weird coloring sometimes. Thanks to TH Morgan, we were able to determine that traits close together on a chromosome are often inherited together. This is why phenotypes like dark hair and light eyes are rarely occurring in humans. TH Morgan discovered this in the correlation between the color of the fly’s body and its wing size. o The linkage is incomplete because of the crossing over process, you can get blue eyes brunettes and short winged black flies, but because the traits are close together, it rarely happens. Messing with chromosome number or structure is a really, really bad idea. It causes disorders, miscarriages, etc. o Nondisjunction is when pairs of homologous chromosomes don’t separate right in anaphase 1 or anaphase 2. This means that at the end of the process, you have one gamete that has zero copies of DNA and one gamete that has two copies. o Aneuploidy is exceedingly common in cancer cells. It occurs when nondisjunct chromosomes get fertilized, they end up with a weird number of chromosomes. They can be trisomic zygotes and have three copies or They can be monosomic zygotes and have one copy o Polyploidy =/= Aneuploidy, in polyploidy, there’s more than 2 sets of full chromosomes. In aneuploidy, they’re not full sets. Polyploidy is common in plants but not in animals, they look more normal than aneuploids so. Triploids have three sets of chromosomes Tetraploids have four full sets of chromosomes When a chromosome breaks, one of these four things happen o Deletion; removal of a segment of the broken chromosome o Duplication; repeat of a segment from the broken chromosome o Inversion; a segment of the broken chromosome is flipped around backwards o Translocation; a segment of the broken chromosome moves somewhere