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Unformatted text preview: Lecture 6 Lecture 6 Lecture 6 Lecture 6 Lecture 6 When we talk about gene position the term locus locus locus locus locus is used to designate the chromosomal location of a gene. What we are going to do is to map genes relative to one another. To begin, we need two genes on the same chromosome. Last lecture we saw how you could tell whether a gene is on the X chromosome by how alleles of the gene are inherited differently by males and females. Consider two mutations on the X chromosome of Drosophila ; crossveinless and white eye. Genotype Phenotype X cv+w+ cv+w+ cv+w+ cv+w+ cv+w+ Y wild type X cv- w+ cv- w+ cv- w+ cv- w+ cv- w+ Y crossveinless wings X cv+w- cv+w- cv+w- cv+w- cv+w- Y white eye X cv-w+ cv-w+ cv-w+ cv-w+ cv-w+ Y x X cv+w- cv+w- cv+w- cv+w- cv+w- X cv+w- cv+w- cv+w- cv+w- cv+w- (true breeding) All of the daughters from this cross will have two different X-chromosomes, which X cv+w- cv+w- cv+w- cv+w- cv+w- X cv-w+ cv-w+ cv-w+ cv-w+ cv-w+ differ at two loci: We want to follow these X chromosomes into the next generation so after a cross we look at male flies. X cv+w- cv+w- cv+w- cv+w- cv+w- Y X cv-w+ cv-w+ cv-w+ cv-w+ cv-w+ Y parental classes: and X cv-w- cv-w- cv-w- cv-w- cv-w- Y X cv+w+ cv+w+ cv+w+ cv+w+ cv+w+ Y crossover classes: and (crossveinless, white) (wild type) In the crossover classes the alleles appear to have separated and moved from one X to the other. Genes on the same chromosome often do not assort independently. Such behavior is known as Linkage Linkage Linkage Linkage...
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This note was uploaded on 09/03/2009 for the course BIOL 7.03 taught by Professor Chriskaiser during the Fall '04 term at MIT.
- Fall '04