Two traits (stem length and seed color) are simultaneously examined in a cross of two pure-breeding pea plant varieties. A tall green plant is crossed with a dwarf yellow plant, and the resulting F1 plants are self-crossed. A total of 640 F2 progeny are phenotypically characterized as follows:
tall yellow = 360
tall green = 120
dwarf yellow = 120
dwarf green = 40
What is the dominance relationship for plant height? for seed color?
What is this asking? Does dominance relationship refer to which allele/phenotype is dominant over the other (in which case, the tall phenotype is dominant over the dwarf phenotype, and yellow seed color is dominant over green seed color)?
Yes, you are correct. The dominance relationship refers to which phenotype is dominant over the other in terms of inheritance. In this case, the "tall" phenotype is dominant over the "dwarf" phenotype, and the "yellow" seed color is dominant over the "green" seed color.
To determine the dominance relationship for plant height and seed color, we can analyze the phenotypic ratios of the F2 progeny.
In the F1 generation, the cross between a tall green plant and a dwarf yellow plant resulted in F1 plants that were all tall and yellow. This indicates that the tall phenotype and yellow seed color are dominant because they appeared in the F1 generation.
Now let's examine the phenotypic ratios in the F2 generation:
- Tall yellow: 360
- Tall green: 120
- Dwarf yellow: 120
- Dwarf green: 40
To determine the dominance relationship for plant height, we compare the tall phenotypes and the dwarf phenotypes. Here, we can see that the tall phenotype appears in both the homozygous tall yellow (360) and heterozygous tall green (120) F2 progeny, while the dwarf phenotype appears in both the homozygous dwarf yellow (120) and homozygous dwarf green (40) F2 progeny. Therefore, we can conclude that the tall phenotype is dominant and the dwarf phenotype is recessive.
To determine the dominance relationship for seed color, we compare the yellow seed color and the green seed color. In this case, we can see that the yellow seed color appears in both the homozygous tall yellow (360) and homozygous dwarf yellow (120) F2 progeny, while the green seed color appears in the heterozygous tall green (120) and homozygous dwarf green (40) F2 progeny. Hence, we can conclude that the yellow seed color is dominant and the green seed color is recessive.
In summary:
- The dominance relationship for plant height: Tall is dominant, and dwarf is recessive.
- The dominance relationship for seed color: Yellow is dominant, and green is recessive.