sex of the plant. Of the species with nonidentical sexchromosomes, a large proportion have an XY system. Forexample, the dioecious plant Melandrium albumhas 22chromosomes per cell: 20 autosomes plus 2 sex chromo-somes, with XX females and XY males. Other dioeciousplants have no visibly different pair of chromosomes; theymay still have sex chromosomes, but not visibly distin-guishable types.Sex-linked patterns of inheritanceCytogeneticists divide the X and Y chromosomes intohomologous and differential regions. Again, let’s use hu-mans as an example (Figure 2-22). The homologousre-gions contain DNA sequences that are substantially sim-ilar on both sex chromosomes. The differentialregionscontain genes that have no counterparts on the other sexchromosome. Hence in males these genes in the differ-ential regions are thus said to be hemizygous(“half zy-492.2 Sex chromosomes and sex-linked inheritanceFemale flowerOvariesonlyAnthersonlyMale flowerplantsplants(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.