only parental combinations survive. For convenience, balancer chromosomes are marked with a dominant morphological mutation. The marker allows the geneti-cist to track the segregation of the entire balancer or its normal homolog by following the presence or absence of the marker. Reciprocal translocations There are several types of translocations, but here we consider only reciprocal translocations, the simplest type. As with other rearrangements, meiosis in heterozygotes having two translocated chromosomes and their normal counterparts produces characteristic conﬁgurations. Fig-ure 15-24 illustrates meiosis in an individual that is het-erozygous for a reciprocal translocation. Notice that the pairing conﬁguration is cross-shaped. Because the law of independent assortment is still in force, there are two common patterns of segregation. Let us use N 1 and N 2 to represent the normal chromosomes, and T 1 and T 2 the translocated chromosomes. The segregation of each of the structurally normal chromosomes with one of the
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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.