1. Figure: 6.1
Title:
Cross of Dwarf and Tall Tobacco Plants
Caption:
Histograms showing the relative frequency of individuals expressing various height phenotypes derived from Kölreuter’s cross between dwarf and tall tobacco plants carried to the F2 generation.

2. Figure: 6.2a
Title:
Cross between Two Strains of Nicotiana
Caption:
The F1, F2, and selected F3 results of East’s cross between two strains of Nicotiana with different corolla lengths. Plants of strain A vary from 37 to 43 mm, while plants of strain B vary from 91 to 97 mm.

3. Figure: 6.2b
Title:
Cross between Two Strains of Nicotiana
Caption:
The F1, F2, and selected F3 results of East’s cross between two strains of Nicotiana with different corolla lengths. Plants of strain A vary from 37 to 43 mm, while plants of strain B vary from 91 to 97 mm.

4. Figure: 6.3
Title:
Multiple-factor Hypothesis
Caption:
How the multiple-factor hypothesis accounts for the 1:4:6:4:1 phenotypic ratio of grain color when all alleles designated by uppercase letters are additive and contribute an equal amount of pigment to the phenotype.

5. Figure: 6.4a
Title:
Polygenic Inheritance
Caption:
The results of crossing two heterozygotes when polygenic inheritance is operative with one to five gene pairs. Each histogram bar indicates a distinct phenotypic class from one extreme (at the left) to the other extreme (at the right). Each phenotype results from a different number of additive alleles.

6. Figure: 6.4b
Title:
Polygenic Inheritance
Caption:
The results of crossing two heterozygotes when polygenic inheritance is operative with one to five gene pairs. Each histogram bar indicates a distinct phenotypic class from one extreme (at the left) to the other extreme (at the right). Each phenotype results from a different number of additive alleles.

7. Figure: 6.5
Title:
Normal Frequency Distribution
Caption:
A normal frequency distribution characterized by a bell-shaped curve.

8. Figure: 6.6
Title:
Two Normal Frequency Distributions
Caption:
Two normal frequency distributions with the same mean but different amounts of variation.

9. Figure: 6.7
Title:
Artificial Selection in Corn
Caption:
Response of corn selected for high and low oil content over 76 generations. The numbers in parentheses along the line for the high oil content indicate the calculation of heritability at these points in the continuing experiment.

10. Figure: 6.8
Title:
DDT-resistant in Drosophila
Caption:
Survival rates of Drosophila carrying combinations of chromosomes from DDT-resistant and DDT-sensitive (control) strains when exposed to DDT. The results indicate that DDT resistance is polygenic, with genes on each of the major chromosomes making a major contribution. (Chromosome 4 carries only a few Drosophila genes and was omitted from this analysis.)

11. Figure: 6.9
Title:
Transgenic Tomatoes
Caption:
Phenotypic effect of the fw2.2 transgene in the tomato. When the allele causing small fruit is transferred to a plant that normally produces large fruit (marked +), the fruit is reduced in size. A fruit (marked -) which is normally larger, is shown for comparison.

12. Figure: 6.UN1
Title:
Problems and Discussion
Caption:
Question 22: A mutant strain of Drosophila is isolated and shown to be resistant to an experimental insecticide, whereas normal (wild-type) flies are sensitive to the chemical. Following a cross between resistant flies and sensitive flies, isolated populations are derived that have various combinations of chromosomes from the two strains. Each population is tested for resistance as shown in the data below. Analyze the data and draw any appropriate conclusion about which chromosomes contain a gene responsible for inheritance of resistance to the insecticide.

13. Figure: 6.UN2
Title:
Problems and Discussion
Caption:
Question 24: Horst Wilkens (Wilkens, H Ecol. Biol. 23: 271–367) investigated blind cavefish, comparing them with members of a sibling species with normal vision that are found in a lake. (We will call them cavefish and lakefish.) Wilkens found that cavefish eyes are about seven times smaller than lakefish eyes. F1 hybrids have eyes of intermediate size. These data as well as the F1 X F1 cross and those from backcrosses (F1 X cavefish and F1 X lakefish) are depicted here: