513Problems20.A new recessive mutant allele doesn’t show pseudo-dominance with any of the deletions that spanDrosophilachromosome 2. What might be the explanation?21.Compare and contrast the origins of Turner syn-drome, Williams syndrome, cri du chat syndrome, andDown syndrome. (Why are they called syndromes?)22.List the diagnostic features (genetic or cytological)that are used to identify these chromosomal alterations:a.Deletionsb.Duplicationsc.Inversionsd.Reciprocal translocations23.The normal sequence of nine genes on a certainDrosophilachromosome is 123?456789, where thedot represents the centromere. Some fruit Fies werefound to have aberrant chromosomes with the fol-lowing structures:a.123?476589123?46789c.1654?32789d.123?4566789Name each type of chromosomal rearrangement, anddraw diagrams to show how each would synapse withthe normal chromosome.24.The two loci Pand Bzare normally 36 m.u. apart onthe same arm of a certain plant chromosome. Aparacentric inversion spans about one-fourth of thisregion but does not include either of the loci. What
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