Monohybrid Cross (Corn 8910)

Transcription

1 AP Biology Corn Genetics and Chi-Square Analysis In this exercise, you will examine an ear of corn and determine the type of cross and genes responsible for the coloration and texture of the corn kernels like the one show below. There are four grain phenotypes in the ear. and smooth (A), and Smooth (B), and Shrunken (C), and Shrunken (D). Monohybrid Cross (Corn 8910) 1. Count the number of purple and yellow kernels in five of the rows on your ear of corn and record the number on the chart. Be sure to use the same five rows for each calculation. 2. Count the number of smooth and shrunken seeds on the same five rows and record on the chart. Number of Kernels Kernel Percentage (divide count by total) Kernel Coloration Kernel Texture Smooth Shrunken 3. What are the probable phenotypes of the parents with regard to coloration? 4. What are the probable phenotypes of the parents with regard to texture?

2 Monohybrid Cross (Corn 8900) 5. Count the number of purple and yellow kernels in five of the rows on your ear of corn and record the number on the chart. Be sure to use the same five rows for each calculation. 6. Count the number of smooth and shrunken seeds on the same five rows and record on the chart. Number of Kernels Kernel Percentage (divide count by total) Kernel Coloration Kernel Texture Smooth Shrunken 7. What are the probable phenotypes of the parents with regard to coloration? 8. What are the probable phenotypes of the parents with regard to texture? Dihybrid Cross (Corn 8915) 9. We will now consider a dihybrid cross, which is a combination of the two monohybrids. Your ear of corn may be a result of a cross between plants that were both heterozygous (PpSs x PpSs). Create a punnett square or use a mathematical system to determine the phenotype ratio. Record what you would expect to get from this cross in the chart below. 10. & smooth & shrunken & smooth & shrunken 11. Now count the number of each in your five rows on the ear of corn. & smooth & shrunken & smooth & shrunken

3 12. Did you obtain a 9:3:3:1 ratio? To determine if the deviations from your observed data are due to chance alone or if the data is significantly different, you need to use a chi square test. The table below will help you make the calculations. & smooth Total x 9/16 = & shrunken Total x 3/16 = & smooth Total x 3/16 = & shrunken Total x 1/16 = 13. Now determine if your chi square value is a good fit with your data. Your degrees of freedom (df) is the number of possible phenotypes minus 1. In your case, 4-1 = 3. Find the number in that row that is closest to your chi square value. Circle 14. Explain what it means to have a "good fit" or a "poor fit". Does you chi square analysis of real corn data support the hypothesis that the parental generation was PpSs x PpSs? Dihybrid Cross (Corn 8907) 15. We will now consider a dihybrid cross, which is a combination of the two monohybrids. Your ear of corn may be a result of a cross between plants that were PpSs x ppss). Create a punnett square or use a mathematical system to determine the phenotype ratio. Record what you would expect to get from this cross in the chart below. This is a dihybrid backcross (or test cross) example. 16. & smooth & shrunken & smooth & shrunken 17. Now count the number of each in your five rows on the ear of corn. & smooth & shrunken & smooth & shrunken

4 18. What ratio did you expect to obtain? Did you obtain this expected ratio? To determine if the deviations from your observed data are due to chance alone or if the data is significantly different, you need to use a chi square test. The table below will help you make the calculations. & smooth Total x = & shrunken Total x = & smooth Total x = & shrunken Total x = 19. Now determine if your chi square value is a good fit with your data. Your degrees of freedom (df) is the number of possible phenotypes minus 1. In your case, 4-1 = 3. Find the number in that row that is closest to your chi square value. Circle 20. Explain what it means to have a "good fit" or a "poor fit". Does you chi square analysis of real corn data support the hypothesis that the parental generation was PpSs x ppss? Mystery Corn (Corn 8920) This ear of corn is an F2 level corn cross result showing the segregation of a dominant aleurone (purple) color gene ( is dominant) and a dominant color-inhibiting gene. This is an example of epistasis. 21. These ears of corn may be a result of a cross between plants that were PyCn x PyCn. (P-purple, y- yellow, C-colored, n-no color) Create a punnett square or use a mathematical system to determine the phenotype ratio. Record what you would expect to get from this cross in the chart below. This is a dihybrid backcross (or test cross) example Now count the number of each in your five rows on the ear of corn.

5 24. What ratio did you expect to obtain? Did you obtain this expected ratio? To determine if the deviations from your observed data are due to chance alone or if the data is significantly different, you need to use a chi square test. The table below will help you make the calculations. Total x = Total x = 25. Now determine if your chi square value is a good fit with your data. Your degrees of freedom (df) is the number of possible phenotypes minus 1. In your case, 2-1 = 1. Find the number in that row that is closest to your chi square value. Circle 26. Explain what it means to have a "good fit" or a "poor fit". Does you chi square analysis of real corn data support the hypothesis that the parental generation was PyCn x PyCn? (Modified from Biology.com Corn Genetics and Chi-square Analysis :