Introduction to Genetic Analysis 475

Introduction to Genetic Analysis 475 - 44200_14_p451-480...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
The molecular mechanism is thought to comprise two key steps: 1. A double-strand break. One key piece of evidence here was that in yeast transformation the incorporation of a circular plasmid into the yeast genome is stimulated 1000-fold when the plasmid is cut to become linear. Broken DNA ends seem to be recombinogenic ; that is, they promote recombination. 2. The formation of heteroduplex DNA. This is a hybrid type of DNA molecule that is composed of a single DNA strand from a chromatid derived from one parent, and a single strand from a chromatid derived from the other parent. The first evidence for heteroduplex DNA was also provided by genetics, specifically ascus analysis. Octads are particularly informative in pointing to the existence of heteroduplexes in crossing-over. We saw in Chapter 2 that in fungi a cross A 3 a will create a monohybrid meiocyte A ± a that is expected to segregate in a 1:1 ra- tio in the meiotic products according to the law of equal segregation. Indeed the 1:1 ratio is found in most fungal meiocytes: we see 4 A and 4 a . However, in rare meiocytes (generally on the order of 0.1 to 1 per-
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

Ask a homework question - tutors are online