Introduction to Genetic Analysis 38

Introduction to Genetic Analysis 38 - 44200_02_p27-72...

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37 2.1 Autosomal inheritance as shown in Figure 2-10. This rather unexpected 9:3:3:1 ratio seems a lot more complex than the sim- ple 3:1 ratios of the monohybrid crosses. What could be the explanation? Before attempting to explain the ratio, Mendel made dihybrid crosses that included several other combinations of characters and found that all of the dihybrid F 1 individuals produced 9:3:3:1 progeny ratios similar to that obtained for seed shape and color. The 9:3:3:1 ratio was another consistent inheritance pattern that required the development of a new idea to explain it. Mendel added up the numbers of individuals in certain F 2 phenotypic classes (the numbers are shown in Figure 2-10) to determine if the monohybrid 3:1 F 2 ratios were still present. He noted that, in regard to seed shape, there were 423 round seeds (315 1 108) and 133 wrinkled seeds (101 1 32). This result is close to a 3:1 ratio. Next, in regard to seed color, there were 416 yellow seeds (315 1 101) and 140 green (108
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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.

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