Radish genetics results

Data analysis

• 1. The first step is to save a copy of the whole class data into a personal spreadsheet so everyone can perform calculations individually.

  2. Do this by opening the Radish Genetics spreadsheet that is within the Radish Genetics folder and save it to your computer in a place that you will remember.

  3. Using the whole-class data, for each treatment, calculate the percent of seedlings that have reddish-purplish stems, and the percent that have yellowish-greenish stems. (To calculate a percent, divide the number of seedlings with the trait by the total number of seedlings in the treatment and multiple by 100). You can accomplish this in Excel by placing your cursor in the cell where you want the percent calculation to occur.

     1. 1. Type”=” into the cell (without the quotes).

        2. Click on the numerator cell.

        3. Type “/” (without the quotes)

        4. Click on the denominator cell.

        5. Type “*100” (without the quotes). Hit enter or the checkmark.

The percentage calculation should appear in that cell. Repeat this for each "Percent with anthocyanin" cell and each "Percent lacking anthocyanin" cell. If you have trouble performing calculations in Excel, you can do the math by hand and then enter the value into the cell instead. Submit this table as part of the "Radish Genetics & Interpretation" test on Blackboard.

Interpretation

Compare your calculations of the percentages for each coloration in each treatment to the expected percentages in both of our hypotheses.

• We saw that the two parental line A (P1) had all non-purple hypocotyls, while parental line B (P2) had nearly all purple hyocotyls. As we discussed, some seeds fail to develop purple stems, even when they have the allele to do so, if the light is insufficiently bright. Given this, we can assume that the parental lines were actually true breeding.

• You previously considered the results of the cross between the two parental strains, one with (mostly) purple-pigmented hypocotyls and one with non-pigmented hypocotyls. If necessary go back and review your conclusions about which trait appeared to be dominant (the trait nearly always expressed in the F1 generation). Record which trait appears to be dominant on the appropriate question in the "Radish Genetics & Interpretation" test (no explanation needed).

• Now that you have a tentative hypothesis about which allele is dominant, make a Punnett square that represents the parental cross and outcome for the F1 generation.

  • If you decided that the purple-pigmentation allele is dominant, then use "P" for the purple allele and p' for the non-pigmented allele.

  • If you decided that non-pigmentation (pale stem) allele is dominant, then use "N" for the non-pigmented allele and "n" for the purple pigmentation allele.

  • Submit this Punnett square on the appropriate question in the "Radish Genetics & Interpretation" test. Use the space bar to align columns. Put the parental alleles in bold and the F1 genotypes not in bold, set up like shown below (this is not the correct cross here, just an example of how to set it up):

  • A a

  • a Aa aa

  • a Aa aa

• Now assume that the genotype of the F1 seeds corresponds to the outcome you determined in the Punnett square for the parental cross that you just made. Make a Punnett square showing a cross between two F1 genotypes to determine the expected genotypes and proportion of each in the F2 generation. Set up the Punnett square like above. Put the alleles for the F1 generation in bold, and the genotypes expected for the F2 generation not in bold, like shown below

  • (this is not the correct cross here, just an example of how to set it up):

A a

a Aa aa

a Aa aa

• Remake the Punnett square for a cross between F1 parents leading to F2 offspring exactly as above, except this time put in the phenotypes of the offspring instead of the genotypes. In other words instead of two capital or lowercase letters in each square, write in the phenotype, like this (but with a stem color, not leaf shape):

A a

a acute obtuse

a acute obtuse

• According to the Punnett square you just made predicting the genotype in the F2 generation, what percent of individuals would you expect to have purple stems. To answer this figure out the phenotype (expected color) for each of the 4 squares, and then figure out the percent of the squares that represent offspring with purple stems - 0%, 25%, 50%, 75% or 100%). Also calculate the percent of individuals that you expect to have non-pigmented stems.

• Now compare the predicted results that you just reported to the actual percentages of the F2 individuals that have pigmented or non-pigmented hypocotyls. Are the percentages similar or not? If there is a difference, are there a higher or lower percentage of individuals in the F2 generation with pigmented hypocotyls than you predicted. If there is a difference, explain why you think that difference occurred.

• Address the following question in a paragraph:

Hairy hypocotyls is another variable trait in radish. Some stems have hairs and some lack them. You can probably see this in the plants in your dishes. Assume that having hairs is dominant (H) and lacking hairs is recessive (h). That means if a plant is hairless, you know its genotype must be hh, but if a plant has hairs, its genotype could be homozygous (HH) or heterozygous (Hh). Imagine that you have a plant with hairs and you want to determine its genotype. You also have a plant lacking hairs. Explain how you could perform a testcross to determine the genotype of the plant with hairs. What would you cross, and what ratios would you expect in the offspring under each hypothesis (the hypothesis that the hairy plant is heterozygous vs. the hypothesis that it is homozygous)?

What to turn in:

• (due previously) Padlet photos of your dishes with sticker and label (P1, P2, F1 and F2)

• (due previously) Data on your counts for each dish to Google Spreadsheet

• Complete the "Radish genetics analysis and interpretation" test to submit your answers for the above questions.