Lab 26 Corn Two Trait Genetics

glossary

26. 1email us

Introduction

Gregor Mendel is called the father of genetics because he analyze his results mathematically. From this data he determined two principles: the Principle of Segregation (which you learned with Wisconsin Fast plants) and the Principle of Independent Assortment. The Principle of Independent Assortment states due to crossing over during meiosis, alleles of a trait will separate into gametes independently of the other traits allowing for all variations to be present.

In this investigation you will count kernels in an ear of corn. A complete ear represents a compact population of offspring which may be counted to show Mendels principle. Mature corn plants produce ears that contain hundreds of seeds or kernels. Each seed is formed through fertilization of a different egg and sperm. Therefore, each kernel on an ear of corn can grow into a whole new plant.

Some grains are purple and others are yellow. The purple color is produced by a pigmented within the grains. If the pigment is not present then the corn is yellow. Sweet corn grains can be recognized because they wrinkle upon drying while starchy grains remain smooth. An individual grain may be purple and starchy, purple and sweet, yellow and starchy, or yellow and sweet. Answer the questions in the prelab.

For extra credit, read about why corn can be speckled on these websites and explain it on the prelab. DNA from the Beginning | Nobel Prize

Parent Generation

F1 generation

F2 generation

http://www.biology-online.org/dictionary.aspmailto:rholsinger@sayreschool.org,dwheeler@sayreschool.orghttp://www.dnaftb.org/dnaftb/32/concept/index.htmlhttp://nobelprize.org/medicine/laureates/1983/press.html

Lab 26 PreLab

Two Trait Corn Genetics

Name:

Pledge:

AUTHORIZED AID: You may discuss questions with classmates or other knowledgeable persons before

composing your OWN answer or you may use a source and cite it appropriately. (12 points)

Directions: Read the introduction in the pdf and pages 47 -48 and 61-64 in The Cartoon Guide to

Genetics. Try the multiple choice questions at the Biology Project. Then answer the questions below.

1. What is the phenotype of each of the labeled corn kernels? (2)

a. FORMDROPDOWN

b. FORMDROPDOWN

c. FORMDROPDOWN

d. FORMDROPDOWN

2. If the parents are homozygous purple and starchy and homozygous yellow and sweet, what are their genotypes? (1ea) FORMDROPDOWN and FORMDROPDOWN

3. Crossing the parent generation results in the first generation (F1). (1ea)

a. What would be the genotype for that first generation? FORMDROPDOWN

b. What would be the phenotype for that first generation? FORMDROPDOWN

4. Below is the F1 cross (self pollination of first generation flowers). Highlight the purple starchy individuals in violet. Highlight the purple sweet individuals in pink. Highlight the yellow starchy individuals in yellow. Highlight the yellow sweet individuals in bright green. The highlight key should be on the formatting toolbar. If yours is not expanded go to View: Toolbars: Formatting. (2)

PS

Ps

pS

ps

PS

PPSS

PPSs

PpSS

PpSs

Ps

PPSs

PPss

PpSs

Ppss

pS

PpSS

PpSs

ppSS

ppSs

ps

PpSs

Ppss

ppSs

ppss

5. Crossing the first generation in the Punnett Square above resulted in the second generation (F2). Count the number of individuals in each phenotypic group and write the expected phenotypic ratio of that second generation in the boxes below. Be sure to include the phenotypes. (2)

: : :

6. After completing the Wisconsin Fast Plant Lab you learned how fruits come from flowers. Is corn appropriately called a fruit or a vegetable?(2) FORMDROPDOWN How do you know?

7. Extra Credit: Why are some of the kernels speckled? To find the answer either check out the websites on the pdf or read pages 175 -178 in The Cartoon Guide to Genetics.

Lab 26 Pre Lab.doc

Lab 26 Corn Two Trait Genetics

glossary

26. 2email us

ProcedureTake a look at the pictures on the previous page. Can you tell if purple or yellow is dominant? How do you know? (hover your mouse over the question mark for the answer)

If you cross a homozygous starchy with a homozygous sweet corn plant, then all the offspring will be starchy. Is starchy or sweet dominant? How do you know?

The ear of corn below shows what you should expect to see during this lab. Count the number of each color and determine if it follows Mendels Principle of Independent Assortment by completing a chi square calculation. Hover over the question marks to see how many kernels counted, the expected numbers and the chi-square critical value. Does the data follow the hypothesis? How do you know?

yellow wrinkled

purple smooth

purple wrinkled

yellow smooth

http://www.biology-online.org/dictionary.aspmailto:rholsinger@sayreschool.org,dwheeler@sayreschool.orgSticky NotePurple is dominant. In the previous slide the parents are purple and yellow, and the offspring is purple. When a homozygous purple plant is crossed with a homozygous yellow plant, the recessive yellow allele disappears in the phenotype of the first generation. When the first generation is crossed, the recessive yellow allele reappears in the phenotype.

Sticky NoteStarchy.

Sticky NoteThe genotype of the offspring must be heterozygous: Ss. In the phenotype the starchy allele masks the sweet allele and therefore the starchy allele must be dominant.

Sticky Note115 are purple starchy, 43 are purple sweet, 40 are yellow starchy and 16 are yellow sweet. There are 214 kernels.

Sticky NoteYou would expect a 9/16 to 3/16 to 3/16 to 1/16 ratio and therefore expect 120 to be yellow starchy, 40 to be yellow starchy, 40 purple sweet, 14 yellow sweet.

Sticky Noteexperimental = 0.676694critcial= 7.82

Sticky Noteyes.

Sticky NoteYou would expect a 9/16 to 3/16 to 3/16 to 1/16 ratio and therefore expect 120 to be yellow starchy, 40 to be yellow starchy, 40 purple sweet, 14 yellow sweet.

Lab 26 Corn Two Trait Genetics

glossary

26. 3email us

Obtain an F2 generation ear of corn. One person should call out the phenotypes while the other tallies them in Table 1 on the answer sheet. Then switch to make sure that each of you know how to determine the phenotypes. Please be careful with the corn cobs as they are fragile; do not remove any of the kernels as you count.

Collect the class data. You will use this website to determine if there is a statistical difference between the observed and expected values. Enter the names of the categories into the first column: red and green. Enter the number of plants counted (observed data) in the second column. Then enter the expected data in the third column. Press the calculate now button.

The next screen will tell you the Chi-Square test statistic and the Degrees of Freedom that you will use to look up the Critical value. It also mentions whether or not the difference between the observed and expected is statistically significant. If the difference is not statistically significant then we have no evidence against Mendels Principle of Segregation; therefore our data follows our hypothesis. Be sure to record this information on your answer sheet and answer the questions.

Dont forget to complete your homework.

Count and record the number of kernels of each phenotype. An individual grain may be purple and starchy, purple and sweet, yellow and starchy, or yellow and sweet. If the kernel is speckled do not count the kernel.

http://www.biology-online.org/dictionary.aspmailto:rholsinger@sayreschool.org,dwheeler@sayreschool.orghttp://graphpad.com/quickcalcs/chisquared1.cfm

Lab 26 Answer Sheet

Two Trait Corn Genetics

Names:

Pledge:

Authorized Aid means you worked TOGETHER to complete this lab answers were discussed with one another before being typed, both participated in conducting the lab procedures, and any sources

or pictures are cited appropriately. (18 total points)

Take a look at this Genetics website to make sure that you understand Mendels Principle of

Independent Assortment. It is also an excellent source of information about many different types of genetics.

1. Assuming that corn follows the principle of independent assortment, what is the phenotypic ratio that you expect in the F2 generation?

: : :

2. After answering the questions in the prelab, and understanding Mendels Principle of Independent Assortment, state a hypothesis to answer the following question. Does corn color and flavor follow Mendels principle of independent assortment? (2)

Results:

Table 1: Tally the number of corn kernels in each category: (5)

Purple Starchy

Purple Sweet

Yellow Starchy

Yellow Sweet

Total kernels counted

Total Ear 1

Table 2: To determine expected values, multiply the total number of plants observed (by your class) by the expected fractions in number 1 above. (4)

Class data

Expected ratios or Statistical proportion

Expected totals

Purple Starchy

Purple Sweet

Yellow Starchy

Yellow Sweet

Total

Statistics:

3. Calculate the chi-square statistic for these data with the calculator program. (2)

In Biology, we use a significance level of 0.05, which is a standard cutoff in statistics. This means there is a 5% chance your experimental counts would differ from your expected counts by at least as much as they do, by chance alone, if your hypothesis is actually correct. The chart below allows you to look up a number, called a critical value, to compare your chi-square statistic to. Since we have 4 categories, there are 3 degrees of freedom.

Critical Values of the Chi-Square Distribution

Degrees of Freedom

Significance Level

1

2

3

4

5

0.05

3.84

5.99

7.82

9.49

11.1

a. Using a significance level of 0.05, the critical value is 7.82. If your calculated chi-square value is less than this number, you don't have evidence against Mendels claim. If your calculated chi-square value is greater than or equal to this number, then there is evidence that Mendels claim is not correct, and you would reject your hypothesis. Can you reject the hypothesis or do you fail to reject t? Explain why. (2)

b. State three experimental errors that could have occurred. (3)

i.

ii.

iii.

Lab 26 Answer Sheet.doc

Lab 26 Homework

Two Trait Corn Genetics

Name:

Pledge:

AUTHORIZED AID: You may discuss questions with classmates or other knowledgeable persons before

composing your OWN answer or you may use a source and cite it appropriately. (13 total points)

Directions: Using your login name and password, access www.explorelearning.com and go to

the "Mouse Genetics (Two Traits).

On the left hand side of the Gizmo are four homozygous mice. You will be looking at two different genes. Black is dominant (F) and white is recessive (f). Black eyes are dominant (E) and red eyes are recessive (e).

Check the box next to Show genotype. Drag a black furred/ black eyed mouse and a white furred/ red eyed mouse into the parent boxes and click Breed. (1 ea)

1. What is the genotype Parent 1? FORMDROPDOWN What gamete can this parent make? FORMDROPDOWN

2. What is the genotype Parent 2? FORMDROPDOWN What gamete can this parent make? FORMDROPDOWN

3. What is the genotype of the offspring? FORMDROPDOWN If you were to use these offspring in an F1 cross what are the four different gametes that they could make? , , ,

Drag three of the children down into the holding cages, and click Clear. Check the box next to Show Statistics. Fill out the following Punnett Square to predict the outcome of your cross. (2)

FE

fE

Fe

fe

4. How many of your offspring do you expect to be the following phenotypes? (1)

a. black furred/ black eyed? FORMDROPDOWN

b. black furred/ red eyed? FORMDROPDOWN

c. white furred/ black eyed? FORMDROPDOWN

d. white furred/ red eyed? FORMDROPDOWN

Now breed the two hybrid mice from the holding cages by dragging them up to the parent boxes and clicking Breed. Breed 1,000 offspring before answer the following questions. (1)

5. What percentage of mice who are

a. black furred and black eyed?

b. black furred and red eyed?

c. white furred and black eyed?

d. white furred and red eyed?

6. How do your results compare to the predicted percentages? (.5)

Drag the remaining hybrid mouse you placed in the holding cage to the parent box. Drag a homozygous white furred, red eyed mice to the other parent box. Fill out the following Punnett Square. (2)

7. From the information in the Punnett Square, how many of your offspring do you expect to be in the following phenotypes. (1)

a. black furred and black eyed?

b. black furred and red eyed?

c. white furred and black eyed?

d. white furred and red eyed?

Now breed the two mice by clicking Breed.

8. How many of the 5 offspring are in the following phenotypes? (1)

a. black furred and black eyed?

b. black furred and red eyed?

c. white furred and black eyed?

d. white furred and red eyed?

9. How do you results compare to the predicted percentages? (.5)

10. What could you do to get results closer to the outcome seen from the Punnett Square? (1)

Lab 26 Homework.doc

Lab 26 Corn Two Trait Genetics

glossary

26. 4email us

References

Corn Dihybrid Genetics. Carolina Biological Supply. Burlington, NC.

Holsinger, Rachel and Debbie Wheeler. Lab 26: Corn Two Trait Genetics. Sayre School: Lexington, KY. April 5, 2015.

Muskopf, Shannan. Corn Genetics and Chi Square Analysis. 2001. The Biology Corner. April 22, 2007. http://www.biologycorner.com/

http://www.biology-online.org/dictionary.aspmailto:rholsinger@sayreschool.org,dwheeler@sayreschool.org

back: Page 1: Page 21: Page 32: Page 43:

forward: Page 1: Page 21: Page 32: Page 43:

Start: Page 1: Page 21: Page 32: Page 43:

bibliography: Page 1: Page 21: Page 32: Page 43: