Introduction to Genetic Analysis 632

Introduction to Genetic Analysis 632 - 44200_19_p611-642...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
in homozygotes. One example is sickle-cell anemia. Indi- viduals with this disorder are homozygous for the allele that codes for hemoglobin-S instead of the normal hemoglobin. They die from a severe anemia because hemoglobin-S crystallizes at low oxygen concentrations, causing the red blood cells to become sickle-shaped and then to rupture (Figure 19-10). As we saw in Chapter 6, another example in hu- mans is phenylketonuria, where tissue degenerates as the result of the accumulation of a toxic intermediate in the pathway of tyrosine metabolism. This case also illus- trates how fitness is altered by changes in the environ- ment. People born with PKU will survive if they observe a strict diet that contains no tyrosine. How selection works Selection acts by altering allele frequencies in a popula- tion. The simplest way to see the effect of selection is to consider an allele a that is completely lethal before re- productive age in homozygous condition, such as the al- lele that leads to Tay-Sachs disease. Suppose that in
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

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.

Ask a homework question - tutors are online