1. William S. Klug Michael R. Cummings Charlotte A
William S. Klug Michael R. Cummings Charlotte A. Spencer Concepts of Genetics Eighth Edition Chapter 4 Extensions of Mendelian Genetics
Copyright © 2006 Pearson Prentice Hall, Inc.

2. Alleles Alter Phenotypes in Different Ways ● wild-type ● loss of function ● null ● gain of function New alleles are produced by mutation

3. Geneticists Use a Variety of Symbols for Alleles

4. In Incomplete Dominance, Neither Allele Is Dominant

5. Figure 4-1 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-1 Incomplete dominance shown in the flower color of snapdragons.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

6. In Codominance, the Influence of Both Alleles in a Heterozygote Is Clearly Evident (but there’s no “blending” of phenotypes.)

7. Multiple Alleles of a Gene May Exist in a Population
The ABO Blood Groups
The A and B Antigens

8. Table 4-1 Copyright © 2006 Pearson Prentice Hall, Inc.
Table 4.1 Potential Phenotypes in the Offspring of Parents with All Possible ABO Blood Group Combinations, Assuming Heterozygosity Whenever Possible
Table Copyright © 2006 Pearson Prentice Hall, Inc.

9. Figure 4-2 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-2 The biochemical basis of the ABO blood groups. The H allele, present in almost all humans, directs the conversion of a precursor molecule to the H substance by adding a molecule of fucose to it. The and alleles are then able to direct the addition of terminal sugar residues to the H substance. The allele is unable to direct either of these terminal additions. Gal: galactose; AcGluNH: N-acetylglucosamine; AcGalNH: N-acetylgalactosamine. Failure to produce the H substance results in the Bombay phenotype where individuals are type O, regardless of the presence of an or allele.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

10. Figure 4-3 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-3 A partial pedigree of a woman displaying the Bombay phenotype. Functionally, her ABO blood group behaves as type O. Genetically, she is type B.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

11. Multiple Alleles of a Gene May Exist in a Population
The White Locus in Drosophila
More than 100 alleles.

12. Table 4-2 Copyright © 2006 Pearson Prentice Hall, Inc.
Table 4.2 Some of the Alleles Present at the white Locus of Drosophila
Table Copyright © 2006 Pearson Prentice Hall, Inc.

13. Lethal Alleles Represent Essential Genes

14. Figure 4-4 Copyright © 2006 Pearson Prentice Hall, Inc.?
Figure 4-4 Inheritance patterns in three crosses involving the normal wild-type agouti allele (A) and the mutant yellow allele in the mouse. Note that the mutant allele behaves dominantly to the normal allele in controlling coat color, but it also behaves as a homozygous recessive lethal allele. The genotype does not survive.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

15. Combinations of Two Gene Pairs Involving Two Modes of Inheritance Modify the 9:3:3:1 Ratio

16. Figure 4-5 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-5 Calculation of the probabilities in a mating involving the ABO blood type and albinism in humans. The calculation is carried out by using the forked-line method.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

17. Fig 4-5 Figure: 04-05a Caption:
Calculation of the probabilities in a mating involving the ABO blood type and albinism in humans. The calculation is carried out by using the forked-line method.

18. Fig 4-5 Figure: 04-05b Caption:
Calculation of the probabilities in a mating involving the ABO blood type and
albinism in humans. The calculation is carried out by using the forked-line method.

19. Phenotypes Are Often Affected by More Than One Gene
Epistasis

20. Figure 4-6 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-6 The outcome of a mating between individuals heterozygous at two genes that determine each individual’s ABO blood type. Final phenotypes are calculated by considering both genes separately and then combining the results using the forked-line method.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

21. Fig 4-6 Figure: 04-06a Caption:
The outcome of a mating between individuals heterozygous at two genes that determine each individuals ABO blood type. Final phenotypes are calculated by considering both genes separately and then combining the results using the forked-line method.

22. Fig 4-6 Figure: 04-06b Caption:
The outcome of a mating between individuals heterozygous at two genes that determine each individuals ABO blood type. Final phenotypes are calculated by considering both genes separately and then combining the results using the forked-line method.

23. Phenotypes Are Often Affected by More Than One Gene
Unique Inheritance Patterns

24. Figure 4-7 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-7 Generation of the various modified dihybrid ratios from the nine unique genotypes produced in a cross between individuals heterozygous at two genes.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

25. Figure 4-8 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-8 The basis of modified dihybrid F2 phenotypic ratios, resulting from crosses between doubly heterozygous F1 individuals. The four groupings of the F2 genotypes shown in Figure 4–7 and across the top of this figure are combined in various ways to produce these ratios.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

26. Figure 4-9 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-9 Summer squash exhibiting various fruit-shape phenotypes, where disc (white), long (orange gooseneck), and sphere (bottom left) are apparent.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

27. Expression of a Single Gene May Have Multiple Effects
Pleiotropy

28. X-Linkage Describes Genes on the X Chromosome

29. Figure 4-11 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-11 The F1 and F2 results of T. H. Morgan’s reciprocal crosses involving the X-linked white mutation in Drosophila melanogaster. The actual data are shown in parentheses. The photographs show white eye and the brick-red wild-type eye color.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

30. Figure 4-12 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-12 The chromosomal explanation of the results of the X-linked crosses shown in Figure 4–11.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

31. Figure 4-13 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-13 (a) A human pedigree of the X-linked color-blindness trait. (b) The most probable genotypes of each individual in the pedigree. The photograph is of an Ishihara color-blindness chart. Red-green color-blind individuals see a 3 rather than the 8 visualized by those with normal color vision.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

32. Table 4-3 Copyright © 2006 Pearson Prentice Hall, Inc.
Table 4.3 Human X-Linked Traits
Table Copyright © 2006 Pearson Prentice Hall, Inc.

33. In Sex-Limited and Sex-Influenced Inheritance, an Individual’s Sex Influences the Phenotype

34. Phenotypic Expression Is Not Always a Direct Reflection of the Genotype
Penetrance and Expressivity

35. Figure 4-16 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-16 Variable expressivity as illustrated by the expression of the eyeless mutation in Drosophila. Gradations in phenotype range from wild type to partial reduction to eyeless.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

36. Figure 4-17 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-17 Position effect, as illustrated in the eye phenotype in two female Drosophila heterozygous for the gene white. (a) Normal dominant phenotype showing brick-red eye color. (b) Variegated color of an eye caused by rearrangement of the white gene to another location in the genome.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

37. Figure 4-17a Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-17a Position effect, as illustrated in the eye phenotype in two female Drosophila heterozygous for the gene white. (a) Normal dominant phenotype showing brick-red eye color. (b) Variegated color of an eye caused by rearrangement of the white gene to another location in the genome.
Figure 4-17a Copyright © 2006 Pearson Prentice Hall, Inc.

38. Figure 4-17b Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-17b Position effect, as illustrated in the eye phenotype in two female Drosophila heterozygous for the gene white. (a) Normal dominant phenotype showing brick-red eye color. (b) Variegated color of an eye caused by rearrangement of the white gene to another location in the genome.
Figure 4-17b Copyright © 2006 Pearson Prentice Hall, Inc.

39. Phenotypic Expression Is Not Always a Direct Reflection of the Genotype
Temperature Effects

40. Figure 4-18 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-18 (a) A Himalayan rabbit. (b) A Siamese cat. Both show dark fur color on the muzzle, ears, and paws. These patches are due to the effect of a temperature-sensitive allele responsible for pigment production at the lower temperatures of the extremities, which is inactive at slightly higher temperatures.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.

41. Figure 4-18a Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-18a (a) A Himalayan rabbit. (b) A Siamese cat. Both show dark fur color on the muzzle, ears, and paws. These patches are due to the effect of a temperature-sensitive allele responsible for pigment production at the lower temperatures of the extremities, which is inactive at slightly higher temperatures.
Figure 4-18a Copyright © 2006 Pearson Prentice Hall, Inc.

42. Figure 4-18b Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-18b (a) A Himalayan rabbit. (b) A Siamese cat. Both show dark fur color on the muzzle, ears, and paws. These patches are due to the effect of a temperature-sensitive allele responsible for pigment production at the lower temperatures of the extremities, which is inactive at slightly higher temperatures.
Figure 4-18b Copyright © 2006 Pearson Prentice Hall, Inc.

43. Phenotypic Expression Is Not Always a Direct Reflection of the Genotype
• Nutritional Effects
• Onset of Genetic Expression
• Genetic Anticipation
• Genomic (Parental) Imprinting

44. Figure 4-19 Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 4-19 The effect of imprinting on the mouse Igf2 gene, which produces dwarf mice in the homozygous condition. Heterozygous offspring that receive the normal allele from their father are normal in size. Heterozygotes that receive the normal allele from their mother, which has been imprinted, are dwarf.
Figure Copyright © 2006 Pearson Prentice Hall, Inc.