Jeff Pinard, a student in Collins's lab, studied more about how CF is inherited. Pinard, shown in Figure 12-1, has CF. Pinard and the rest of Collins's group were able to study the CF gene in part because of work carried out by geneticists in the early 1900s.

Early Work

In the early 1900s, researcher Thomas Hunt Morgan began experimenting with the small fruit fly Drosophila melanogaster. Morgan observed that the flies have four pairs of chromosomes. He also observed that three of the pairs were identical in both females and males, but one pair differed in size and shape. In females, the fourth pair had two identical chromosomes, now called X chromosomes. In males, the fourth pair had one X chromosome, but also a shorter chromosome, now called a Y chromosome. Today, geneticists call the X and Y chromosomes sex chromosomes.

figure 12-1


• Distinguish between sex chromosomes and autosomes.

• Explain the role of sex chromosomes in sex determination.

• Describe how an X- or Y-linked gene affects the inheritance of traits.

• Explain the effect of crossing-over on the inheritance of genes in linkage groups.

• Distinguish between chromosome mutations and gene mutations.

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