Me n d e l s P e a s Exer c i se 1 - Par t 1

Transcription

1 !! Me n d e l s P e a s Exer c i se 1 - Par t 1 TR UE - BR E E D I N G O R G A N I S M S Go a l In this exercise you will use StarGenetics, a genetics experiment simulator, to understand the concept of true breeding in genetics by examining a specific genetic trait, flower color, in pea plants. Le a r ni ng obj e c t i ve s After completing this exercise, you will be able to: 1. Perform genetics experiments in the genetics cross simulator, StarGenetics. 2. Explain what it means for an organism to be true breeding. 3. Determine if an organism is true breeding through the analysis of results from genetic crosses. 4. Determine if individual organisms are homozygous or heterozygous for a given trait through the analysis of results from genetic crosses. Ge t t i n g s t a r t e d w i t h S t a r Ge n e t i c s To access StarGenetics, please navigate to: ht t p: / / st a r.m i t.e d u / g e n e t i c s /. Click on the St a r t button to launch the application. Click Tr us t when a prompt appears asking if you trust the certificate. Click on Fi l e! Ne w in the drop-down menu in the upper left hand corner. Click on the Me n d e l s P e a s Ex er ci se 1 Pa r t 1 file. You are working in a company that produces strains of pea plants and ships them out all over the world to research labs. Your company prides itself on supplying only true-breeding pea plants that produce identical pea plant offspring for many generations. Your co-worker has developed two new lines of pea plants that he believes are true breeding: one with wh i t e f l o we r s and one with pur pl e f l ow e r s. Your current project is to confirm that the white- and purple-flowered pea plants are true breeding before the pea plants are shipped to researchers around the world. To conduct this project, you have been given two pea plants in the St r a i ns box of StarGenetics: Wh it e P a r e n t 1 and Pur pl e Pa r e nt 1. 1 You will begin this project by determining whether Wh i t e P a r e n t 1 is true breeding through an analysis of its offspring. Some plants, including the pea plants you are working with, have the ability to self-cross. This means that a single plant can generate offspring all on its own by producing both the sperm (pollen in plants) and the eggs (ovum) within each flower or within separate flowers on the same plant. a) What is/are the flower color phenotype(s) of the F1 offspring resulting from the self-cross of Wh i t e Pa r e nt 1? Self-cross Wh i t e P a r e n t 1 by dragging Wh i t e P a r e n t 1 to the Ma t i n g s it e twice, to act as both the ovum and pollen donor, and then click on the Ma t e button to generate F1 offspring. Each resulting offspring can be viewed within the In d iv id u a l tab. A summary of the results is available in the Sum m a r y tab. The flower color of individual offspring can be visually observed or obtained by selecting an offspring of interest and looking in the Pr ope r t i e s window. Ver. 17 L. Weingarten 1

2 Phe not y pe ( s ) : White flower b ) What is/are the flower color phenotype(s) of the F1 offspring from the previous cross when you analyze an additional 72 F1 progeny (for a total of 80)? Analyze a total of 80 F1 offspring by performing an additional 9 self-crosses. To add additional offspring to a cross, click on the Ad d m o r e m at i n gs button and select the appropriate number of matings (or crosses) you would like to perform in the pop-up window to add the appropriate number of additional offspring. Rename this experiment by clicking the box with the current experiment name at the top of the A ct i ve e xp er i m en t window and enter the new experiment name, WP S e l f, when prompted. This will allow you to more easily keep track of your multiple experiments. Phe not y pe ( s ) : White flower c ) When a plant is true breeding, all subsequent generations will also have the same, identical phenotype as the parent plant. Because it is incredibly important to guarantee that the plants your company is selling are true breeding, you decide to generate subsequent generations of Wh i t e P a r e n t 1 by self-crossing the offspring of each subsequent cross. i. What is/are the flower color phenotype(s) of the F2 progeny when you self-cross two F1 plants? To start a new mating experiment, click on the Ne w e xp er i m en t button. Your current experiment will automatically be saved for you. You can cross individual pea plants that you have generated in a previous saved experiment by dragging them from the appropriate Sa ve d e xp er i m en t s window to the M at i n g si t e. Self-cross an F1 individual of your choice from the WP S e l f experiment in the Sa ve d e xp er i m en t s Rename this experiment WP F Self-cross a second F1 individual of your choice from the WP S e l f experiment in the Sa ve d e xp er i m en t s Rename this second experiment WP F Na m e o f 1 s t F1 p l an t s el f ed : WP S e l f -1 F2 P h en o t yp e( s ) : White flower Na m e o f 2 n d F1 p l an t s el f ed : WP S e l f -2 F2 P h en o t yp e( s ) : White flower ii. What is/are the flower color phenotype(s) of the F3 progeny when you self-cross two F2 plants? Self-cross an F2 individual of your choice from the WP F 1. 1 experiment in the Sa ve d e xp er i m en t s Rename this experiment WP F Self-cross an F2 individual of your choice from the WP F 1. 2 experiment in the Sa ve d e xp er i m en t s Rename this second experiment WP F Ver. 17 L. Weingarten 2

3 Na m e o f 1 s t F2 p l an t s el f ed : WP F1.1-1 F3 P h en o t yp e( s ): White flower Na m e o f 2 n d F2 p l an t s el f ed : WP F1.2-1 F3 P h en o t yp e( s ): White flower d ) Is Wh i t e P a r e n t 1 true breeding? Why or why not? ( C i r c l e o n e ) Ye s No Wh y o r w h y not? Because after we had done the self- cross in both white flower parent 1 and its offsprings (first F1 and second F1 and also first F2 and second F2) for 80 times in each, the offsprings of each generation are still be white flower. These show that in the next and next generation of crossing, we will get only the phenotype of white flower so the white parent 1 is true breeding. 2 Next, you would like to determine whether the Pur pl e Pa r e nt 1 plant is true breeding. a) What is/are the flower color phenotype(s) of the F1 offspring resulting from a self-cross of Pur pl e Pa r e nt 1? Perform a self-cross of Pur pl e Pa r e nt 1 producing a total of 80 offspring. Rename this experiment PP 1 S el f. Phe not y pe ( s ) : Purple flower b) To determine if the Pur pl e Pa r e nt 1 plant is true breeding, you also need to test the flower color phenotypes of subsequent generations of offspring. i. What is/are the flower color phenotype(s) of the F2 progeny when you self-cross two F1 plants? Self-cross an F1 individual of your choice from the PP 1 Se l f experiment in the Sa ve d e xp er i m en t s Rename this experiment PP 1 F1. 1. Self-cross a second F1 individual of your choice from the PP 1 Se l f experiment in the Sa ve d e xp er i m en t s Rename this second experiment PP 1 F1. 2. Na m e o f 1 s t F1 p l an t s el f ed : PP 1 Self-1 F2 P h en o t yp e( s ) : Purple flower Na m e o f 2 n d F1 p l an t s el f ed : PP 1 Self-2 F2 P h en o t yp e( s ) : Purple flower Ver. 17 L. Weingarten 3

4 ii. What is/are the flower color phenotype(s) of the F3 progeny when you self-cross two F2 plants? Name: Thaksaporn (May) Self-cross an F1 individual of your choice from the PP1 F 1. 1 experiment in the Sa ve d e xp er i m en t s Rename this experiment PP1 F Self-cross an F1 individual of your choice from the PP1 F 1. 2 experiment in the Sa ve d e xp er i m en t s Rename this second experiment PP1 F Na m e o f 1 s t F2 p l an t s el f ed : PP 1 F1.1-1 F3 P h en o t yp e( s ) : Purple flower Na m e o f 2 n d F2 p l an t s el f ed : PP 1 F1.2-1 F3 P h en o t yp e( s ) : Purple flower c) Is Pur pl e Pa r e nt 1 true breeding? Why or why not? ( C i r c l e o n e ) Ye s No Wh y o r w h y n o t? Because after we had done the self- cross in both purple flower parent 1 and its offsprings (first F1 and second F1 and also first F2 and second F2) for 80 times in each, the offsprings of each generation are still be purple flower. These show that in the next and next generation of crossing, we will get only the phenotype of purple flower so the purple parent 1 is true breeding. 3 Assuming that flower color is determined by a single gene in pea plants: - Is Wh i t e P a r e n t 1 homozygous or heterozygous with regard to the flower color gene? - Is Pur pl e Pa r e nt 1 homozygous or heterozygous with regard to the flower color gene? Note: You do not need to indicate the exact genotype for either plant, just think about whether the two alleles are the same or different for flower color. Hom o z y g o u s means the organism has two copies of the same genetic variation, or allele, for a given trait. Therefore, a homozygous organism for a given trait can only pass on this one allele to its offspring. Het e r o z y g o u s means the organism has two different variations, or alleles, for a given trait. It can pass on either allele of the trait to its offspring. ( c i r c l e t h e a p p r o p r i a t e a n s w e r s ) Is t h e g e n o t y p e o f Pur pl e Pa r e nt 1 : Ho m o z y g o u s He t e r o z y g o u s Bo t h Is t h e g e n o t y p e o f Wh i t e P a r e n t 1 : Ho m o z y g o u s He t e r o z y g o u s Bo t h 4 Another pea plant with purple flowers (Pur pl e Pa r e nt 2 ) is mysteriously left on your desk from a secret admirer. The first thing you want to do with this plant, of course, is to determine whether this plant can be added to a collection of true-breeding plants. Ver. 17 L. Weingarten 4

5 a) To determine if the plant is true breeding, you must analyze the F1, F2, and F3 offspring. i) What is/are the flower color phenotype(s) of the F1 offspring resulting from a self-cross of the Pur pl e Pa r e nt 2 plant? Self-cross Pur pl e Pa r e nt 2 and record the flower color phenotype(s) of 80 F1 progeny. Rename this experiment PP2 S el f. F1 P h en o t yp e( s ) : 59 progeny flowers (74%) are purple but 21 progeny are white (26%) ii. What is/are the flower color phenotype(s) of the F2 progeny when you self-cross two F1 plants? Self-cross an F1 individual of your choice from the PP2 S el f experiment in the Sa ve d e xp er i m en t s Rename this experiment PP2 F Self-cross a second F1 individual of your choice from the PP2 s e l f experiment in the Sa ve d e xp er i m en t s Rename this second experiment PP2 F Na m e o f 1 s t F1 p l an t s el f ed : PP2 Self-1 F2 P h en o t yp e( s ) : 64 progeny flowers (80%) are purple but 16 progeny are white (20%) Na m e o f 2 n d F1 p l an t s el f ed : PP2 Self-2 F2 P h en o t yp e( s ) : all of them are white flowers iii. What flower color phenotype(s) do you observe for the F3 progeny of this Pur pl e Pa r e nt 2 plant? Self-cross an F1 individual of your choice from the PP2 F 1. 1 experiment in the Sa ve d e xp er i m en t s Rename this experiment PP2 F Self-cross an F1 individual of your choice from the PP2 F 1. 2 experiment in the Sa ve d e x pe r i m e nt s Rename this second experiment PP2 F Na m e o f 1 s t F2 p l an t s el f ed : PP2 F F3 P h en o t yp e( s ) : all of them are purple flowers Na m e o f 2 n d F2 p l an t s el f ed : PP2 F F3 P h en o t yp e( s ) : all of them are white flowers Ver. 17 L. Weingarten 5

6 b) Is Pur pl e Pa r e nt 2 true breeding? Why or why not? ( C i r c l e o n e ) Ye s No Wh y o r w h y n o t? Because after self- cross the purple parent 2 and get F1 progeny, not all if the progeny are purple but 59 flowers (74%) are purple and 21 progeny are white (26%) so it has already showed that the purple parent 2 is not true breeding. 5 Based on your results from Question 4, is Pur pl e P ar e nt 2 homozygous or heterozygous with regard to the flower color gene? Do the Pur pl e Pa r e nt 1 and Pur pl e Pa r e nt 2 pea plants have the same genotype? Explain. Ver. 17 L. Weingarten 6

7 No t e : You do not need to indicate the actual genotype of the parents. Instead, think about whether the alleles are the same or different in each parent. ( c i r c l e t h e a p p r o p r i a t e a n s w e r s ) The g e no t y p e o f Pur pl e Pa r e nt 2 is : Ho m o z y g o u s He t e r o z y g o u s The g e no t y p e s o f t he Pur pl e Pa r e nt 1 an d Pur pl e Pa r e nt 2 pe a pl a nt s a r e : The S a m e Di f f e r e n t Wh y? Because the two copy alleles of the purple parent 1are the same genetic variation so the allele of a same trait (homozygous organism) is given to its offspring and the phenotype of its subsequence generations will still be purple. In contrast, the genotype of purple parent 2 is heterozygous which means it will has two different alleles which are white and purple and when the alleles are passed through its offspring, it can pass on either allele of the trait to its offspring. Therefore, the phenotypes of the subsequence generation are both white flowers and purple flowers. Ver. 17 L. Weingarten 7