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BIO 325 September 16th Lecture Notes

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BIO 325
Sanghamitra Mohanty

9/16 Lecture Friday, September 13, 2013 2:07 PM Mendel's principle of independent assortment applies to situations in which two modes of inheritance occur simultaneously, provided that the genes controlling each character are not linked on the same chromosome. Gene interaction - the cellular function of numerous gene products contributes to the development of a common phenotype  Many traits characterized by a distinct phenotype are affected by more than one gene Epistasis - effect of one gene or gene pair modifies or masks the effect of another gene or gene pair  The gene that modifies is known as the epistatic gene  The gene that gets modified is hypostatic gene  Example: Bombay phenotype o Mutation of FUT1 affected the expression of the main gene  Often arise because two or more different proteins participate in a common cellular function o Example: enzymatic pathway  Colorless precursor ----------(enzyme C)---------> colorless intermediate ---------(enzyme P)----------> purple pigment Novel phenotypes - gene interaction produces new phenotypes in the F2 generation in addition to producing a modified dihybrid ratio Example: fruit shape in summer squash  2 genes at 2 different loci determines the fruit shape of squash  Disc-shaped fruit (AABB) x long fruit (aabb) o F1 is all disc-shaped fruit o F2 includes both parental phenotype plus spherical variants in 9:6:1 ratio  9/16 A-B- disc  3/16 A-bb sphere, 3/16 aaB- sphere  1/16 aabb long o Disc fruits require dominant alleles at BOTH LOCI Complementation analysis - look at one phenotype and the interaction of two genes  If mutations affect the same gene are alleles of each other, no normal product of the gene is produced  If two recessive mutations are in separate genes and aren't alleles, the normal copies of these two genes complement one another and restore the wild-type phenotype Pleiotropy - when expression of a single gene has multiple phenotypic effects, and it's quite common  Example: Marfan syndrome o Mutation of the gene fibrillin [it encodes for collagen] o Specific symptoms are developed  Lens of the eyes is soft and gets dislocated in the chamber of the eye  Long and slender bones  The biggest blood vessel of the body (aorta -- walls are made of collagen) is affected  Example: porphyria variegata o Cannot metabolize porphyrin --- deep red urine o Becomes toxis to brain (abdominal pain, muscular weakness, fever, insomnia, headaches) o King George III of England had this Genes present on the X chromosome exhibit unique patterns of in
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