Compose a response to the following questions. Enter both question and answers in your Learning Journal.

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 F2 generation: 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?

Ans.

1. The most important precaution to be implemented that both the parents- one with dominant traits, and the other with recessive traits- must be pure breeding, i.e. homozygous at the respective loci.   

2. Phenotypic ration:

Tall/inflated : Tall/constricted : Dwarf/ inflated : Dwarf constricted

            = 2706 : 930 : 888 : 300                   ; [divide by ratios by 300]

            = 9.02 : 3.1 : 2.96 : 1             ; [convert the values to nearest whole number]

            = 9 : 3: 3: 1

Yes, the ratio is consistent in Mendel’s F2 ration.

3. Yes, the result was close to the expected 9 :3 :3 :1 ratio.

Yes, the result supports the predications – “the traits follow Mendelian inheritance pattern”.

If far fewer plants were used, the calculated phenotypic ration would have exhibited much larger deviations from Mendelian F2 ratio of 9: 3: 3: 1.

 The potentials for experimental errors may include-

A. Cross pollination: Note that pea plants are self-pollinated naturally. So, extremely windy conditions may not affect self-pollination of F1.

However, it may cause falling of the flowers and therefore loss of several F2 progeny that could develop from those flowers.

If it happens, the observed F2 ratio would show deviation from expected ration.

B. Loss of plants or seeds in any form (disease, herbivory, etc.) ultimately causes loss of F2 progeny. It would cause deviation from expected F2 ration.