chromatids - of segregation) occurs in meiosis. In the...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1120/11 Crossing over occurs in tetrads during prophase I ofmeiosis. More specifically, it starts in Pachynema and finishes in Diakineses of prophase I. Importantly, each crossover event affects only 2 ofthe 4 chromatids of a tetrad. This last point is important, first because it helps to explain why the observed recombination frequency of linked genes cannot exceed 50%. That is, the recombination frequency (RF) of linked genes depends on the crossover frequency. Each crossover event can only affect half (2 of the 4) ofthe chromatids of the tetrad. Thus, 50% ofthe chromatids of each crossover event will remain unaffected. This limits the recombination frequency to the 50% of the chromatids that are affected by the crossover. In turn, this limit restricts the RF to an asymptote of 50%. This point is also important, because it complicates our argument as to when Mendel's first law (the law
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: of segregation) occurs in meiosis. In the ABSENCE of crossover, the first law occurs in anaphase I. Note in the picture below how the "A" alleles are being separated (segregated) from the "a" alleles in Anaphase I. However, ifthere is crossover in prophase I, note in the picture below how the "A" and "a" alleles are no longer separated from each other at the end ofmeiosis L Instead, the "A" and "a" alleles now must "wait" until anaphase II for their segregation (during which chromatids become separated as distinct chromosomes). fropl,,())c-r ffOP k~s~ I £~J of Me: "OSI'~ r. ( "~.f-61 {. <:.f Q $<;, -(o,fi-e( (.,(05$-(klL. .tett C~fOMOSO"'~~ tVI1JIJ", "'ll~lA~ oVLr) .o.;~ f ) ~s " f kit! C~(JI,/s~c tL.~ ..... ) .... In conclusion, when there is no crossover, then the law of segregation occurs in anaphase 1. However, when crossover occurs, then this law occurs in anaphase II. L...
View Full Document

This note was uploaded on 06/08/2011 for the course PCB 3063 taught by Professor Marta during the Spring '08 term at University of Florida.

Page1 / 2

chromatids - of segregation) occurs in meiosis. In the...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online