lhttps://cnx.org/contents/GFy_h8cu@9.85:cUeevuaC@3/Laws-of-Inheritance This is t
ID: 205226 • Letter: L
Question
lhttps://cnx.org/contents/GFy_h8cu@9.85:cUeevuaC@3/Laws-of-Inheritance This is the link to the picture.
Testing the Hypothesis of Independent AssortmentTo better appreciate the amount of labor and ingenuity that went into Mendel’s experiments, proceed through one of Mendel’s dihybrid crosses. Question: What will be the offspring of a dihybrid cross? Background: Consider that pea plants mature in one growing season, and you have access to a large garden in which you can cultivate thousands of pea plants. There are several true-breeding plants with the following pairs of traits: tall plants with inflated pods, and dwarf plants with constricted pods. Before the plants have matured, you remove the pollen-producing organs from the tall/inflated plants in your crosses to prevent self-fertilization. Upon plant maturation, the plants are manually crossed by transferring pollen from the dwarf/constricted plants to the stigmata of the tall/inflated plants. Hypothesis: Both trait pairs will sort independently according to Mendelian laws. When the true-breeding parents are crossed, all of the F1 offspring are tall and have inflated pods, which indicates that the tall and inflated traits are dominant over the dwarf and constricted traits, respectively. A self-cross of the F1 heterozygotes results in 2,000 F2progeny. Test the hypothesis: Because each trait pair sorts independently, the ratios of tall:dwarf and inflated:constricted are each expected to be 3:1. The tall/dwarf trait pair is called T/t, and the inflated/constricted trait pair is designated I/i. Each member of the F1 generation therefore has a genotype of TtIi. Construct a grid analogous to Figure, in which you cross two TtIi individuals. Each individual can donate four combinations of two traits: TI, Ti, tI, or ti, meaning that there are 16 possibilities of offspring genotypes. Because the T and I alleles are dominant, any individual having one or two of those alleles will express the tall or inflated phenotypes, respectively, regardless if they also have a t or i allele. Only individuals that are tt or ii will express the dwarf and constricted alleles, respectively. As shown in Figure, you predict that you will observe the following offspring proportions: tall/inflated:tall/constricted:dwarf/inflated:dwarf/constricted in a 9:3:3:1 ratio. Notice from the grid that when considering the tall/dwarf and inflated/constricted trait pairs in isolation, they are each inherited in 3:1 ratios. This figure shows all possible combinations of offspring resulting from a dihybrid cross of pea plants that are heterozygous for the tall/dwarf and inflated/constricted alleles. Test the hypothesis: You cross the dwarf and tall plants and then self-cross the offspring. For best results, this is repeated with hundreds or even thousands of pea plants. What special precautions should be taken in the crosses and in growing the plants? Analyze your data: You observe the following plant phenotypes in the F2generation: 2706 tall/inflated, 930 tall/constricted, 888 dwarf/inflated, and 300 dwarf/constricted. Reduce these findings to a ratio and determine if they are consistent with Mendelian laws. Form a conclusion: Were the results close to the expected 9:3:3:1 phenotypic ratio? Do the results support the prediction? What might be observed if far fewer plants were used, given that alleles segregate randomly into gametes? Try to imagine growing that many pea plants, and consider the potential for experimental error. For instance, what would happen if it was extremely windy one day?
Explanation / Answer
What will be the offspring of a dihybrid cross?
Answer
tall/inflated, tall/constricted, dwarf/inflated, and dwarf/constricted
Test the hypothesis
For the best results, for producing F1 palnts we need to avoid self fertilization by remove the pollen-producing organs from the tall/inflated plants.
Growing the plants in the isolated place.
No cross contamination between outside pollen grains through winds or bees.
Analyze the data
2706 tall/inflated, 930 tall/constricted, 888 dwarf/inflated, and 300 dwarf/constricted.
9.02 tall/inflated, 3.1 tall/constricted, 2.96 dwarf/inflated, and 1 dwarf/constricted.
The approximate ratio 9:3:3:1.
Yes it is consistent with Mendelian laws.
From a conclusion
1. Yes the result is close to the expected 9:3:3:1 phenotypic ratio.
2. Yes, the results support the prediction
3. If we used only fewer plants we not able to get the phenotypic ratio what actually expected. Due to small population there might be error in the outcomes.
4. If many pea palnts are growing in the field there is some times experimental error will happen if not label properly in the plants. 2000 plants if we have to analysis ,eans definetly there is a chance for error.
5. if it was extremely windy one day means most of the pods will be comes out from the plants and further continuity of the project will be halted.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.