BISC 202 Lecture Notes - Lecture 11: Euchromatin, Heterochromatin, X-Inactivation

• School: Simon Fraser University
• Department: Biological Sciences
• Course: BISC 202
• Professor: Carol Wenzel

Document Summary

Genetic background and the environment may alter phenotypic expression: pe(cid:374)etra(cid:374)(cid:272)e- the percentage of genotypically mutant individuals that show at least some expression of the character; for fully penetrant trait= 100%. Incomplete penetrance (i. e. <100%) can lead to misclassification of some individuals as wildtype (a problem for analysis of pedigrees): e(cid:454)pressi(cid:448)it(cid:455)- measure of the degree of expression of the character by genotypically mutant individuals. Variability in expressivity is also a problem for studying gene interaction and pedigree analysis. Variable penetrance: not everyone expresses the mutation, but those who do show the full phenotype. Variable expressivity: everyone shows a mutant phenotype but some to a lesser degree. Variable penetrance and expressivity: not everyone shows the trait, and those who do show variable phenotypes. Flies that are homozygous for a recessive eyeless mutation can: be phe(cid:374)ot(cid:455)pi(cid:272)all(cid:455) normal (top, ha(cid:448)e s(cid:373)all e(cid:455)es (cid:894)(cid:373)iddle(cid:895, ha(cid:448)e (cid:374)o e(cid:455)es (cid:894)(cid:271)otto(cid:373)(cid:895) We know individual q is carrying the dominant allele. Some pedigrees show both variable penetrance and expressivity.