Introduction to Genetic Analysis 50

Introduction to Genetic Analysis 50 - 44200_02_p27-72...

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sex of the plant. Of the species with nonidentical sex chromosomes, a large proportion have an XY system. For example, the dioecious plant Melandrium album has 22 chromosomes per cell: 20 autosomes plus 2 sex chromo- somes, with XX females and XY males. Other dioecious plants have no visibly different pair of chromosomes; they may still have sex chromosomes, but not visibly distin- guishable types. Sex-linked patterns of inheritance Cytogeneticists divide the X and Y chromosomes into homologous and differential regions. Again, let’s use hu- mans as an example (Figure 2-22). The homologous re- gions contain DNA sequences that are substantially sim- ilar on both sex chromosomes. The differential regions contain genes that have no counterparts on the other sex chromosome. Hence in males these genes in the differ- ential regions are thus said to be hemizygous (“half zy- 49 2.2 Sex chromosomes and sex-linked inheritance Female flower Ovaries only Anthers only Male flower plants plants (a) (b) Figure 2-21 Two dioecious plant species.
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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.

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