Investigating Mendelian Genetics with Wisconsin Fast Plants Lab, Lab Reports of Biology

Download Investigating Mendelian Genetics with Wisconsin Fast Plants Lab and more Lab Reports Biology in PDF only on Docsity!

Investigating Mendelian Genetics

with Wisconsin Fast Plants™

Investigating Mendelian Genetics with Wisconsin Fast Plants™

Table of Contents

Introduction to Investigating Mendelian Genetics with Wisconsin Fast Plants™ 4

Wisconsin Fast Plants™ Genetics Background Information 4

Growing Tips (See Growing Instructions for complete guide) 5

Terminology 5

Genetics Activities Overview 6

Monohybrid Activity Overview 6

Monohybrid Activity 8

Genetics Investigation Procedure 8

Discussion Questions 9

Dihybrid Genetics Activity 10

Chi-Square Test 13

For additional activities, student pages and related resources, please visit the Wisconsin Fast Plants’ website at www.fastplants.org

Investigating Mendelian

Genetics with Wisconsin

Fast Plants™

Welcome to the wonderful world of Wisconsin Fast Plants™ and investigations to engage students in studying Mendelian genetics with hands-on experimentation. Originating from decades of innovative research by Professor Paul Williams at the University of Wisconsin- Madison, Wisconsin Fast Plants™, Brassica rapa, are now used by millions of students worldwide.

The investigations in this booklet were designed for students to develop understanding of the following biological concepts and skills:

• Mendel’s law of segregation and law of independent assortment
• Inheritance of 2 traits
• How genotypes influence phenotypes
• Scientific inquiry, including interpretation of evidence

Wisconsin Fast Plants™ Genetics Background Information

Phenotypes and Genotypes

Rapid-cycling Brassica rapa has been designated the cultivar name “RCBr.” Anthocyanin is a purple pigment found in many plants, including Wisconsin Fast Plants™. Anthocyanin is best observed when the plants are 4-7 days old. Look on the stems and hypocotyls, under the cotyledons, and at the leaf tips. A single gene, the anthocyaninless gene (anl), in Wisconsin Fast Plants™ regulates whether or not anthocyanin will be expressed. In the homozygous, recessive form (anl/anl), anthocyanin expression is completely suppressed, and the plants appear a bright green color (which is the “non-purple stem ”

phenotype). If the genotype is anl/ANL or ANL/ ANL, then anthocyanin is expressed at varying levels and the plants are the “purple stem” phenotype. The genotype of the wild type is ANL/ANL.

The yellow-green gene (ygr) in Wisconsin Fast Plants™ determines whether the leaves will be yellow-green or green in color. In the homozygous, recessive form (ygr/ygr), the leaves appear a pale, yellow-green color (which is the “yellow-green leaf” phenotype). If the genotype is ygr/YGR or YGR/YGR, then the leaves appear green (which is the “green leaf” phenotype). The genotype of the wild type is YGR/YGR.

The rosette mutant stock is Wisconsin Fast Plants™ stock that is homozygous for the recessive mutant gene, ros, a conditioning deficiency in gibberellin that results in a short, rosette plant form. In the homozygous, recessive form (ros/ros), the plants have the rosette form. If the genotype is ros/ROS or ROS/ROS, then the plants have the standard form. The genotype of the wild type is ROS/ ROS.

(Note: The rosette phenotype can be induced to grow normally by applying exogenous gibberellin in the form of gibberellic acid.)

Growing Tips

(See Growing Instructions for complete guide)

• To ensure high seed yields and to optimize expression of the genetic traits used in this investigation, follow the Growing Instructions carefully
• It is easiest to observe the purple color on the hypocotyls (stems) when the plants are 4-7 days old
• The intensity of purple color is affected by the environment More light yields a deeper purple color, as does reduced fertilizer
• Do not germinate Yellow-Green Leaf plants in Petri plates The yellow-green color is virtually indistinguishable from the green color when seeds are germinated in Petri plates Use a soil medium instead
• Expect an approximate 9:3:3:1 ratio of plants in the F 2 generation Due to the random nature of gamete segregation, an exact 9:3:3:1 ratio is unlikely to be observed Use the ratio as a foundation for understanding the Law of Segregation

Terminology

P 1 = maternal parent

P 2 = paternal parent

F 1 = first-generation offspring, the result of crossing P 1 and P 2 plants

F 2 = second- generation offspring, the result of intermating the F 1 plants

Genetics

Monohybrid Activity Overview

In this activity, students will observe three generations of Wisconsin Fast Plants™; students will investigate paternity by observing phenotype and inferring genotype.

This investigation spans the entire life cycle of the mother and father (parent) generation (P 1 and P 2 ) and the first-generation offspring (F 1 ) of plants; and an additional nine days allow students to observe the second generation offspring (F 2 ). This activity is designed for students to investigate the inheritance of a single gene in Wisconsin Fast Plants™.

Note: To ensure success of the plants — and to optimize conditions for expression of the genetic traits used in this investigation — it is important that you carefully follow the enclosed Wisconsin Fast Plants™ Growing Instructions flyer.

Materials

Wisconsin Fast Plants™ seeds - Seeds of two generations are included: wild-type RCBr seeds (P 1 ) (non-purple stem, green, standard) mutant-type seeds (P 2 ) (purple stem [anl/anl], yellow-green [ygr/ygr], or rosette [ros/ros]) F 1 non-purple stem, yellow-green leaf growing systems

Each growing system includes:

• 1 circular watermat
• 1 long watermat wick
• 1 small container
• 1 large container (reservoir)
• 4 pots
• 4 small blue watermat wicks
• potting mix
• fertilizer
• stakes and ties
• labels

Three Possible Mutants

1. Anthocyaninless - mutant gene anl in the homozygous condition, anl/anl, blocks the expression of anthocyanin (results in completely green seedlings). 2. Yellow-green - mutant gene ygr in the homozygous condition, ygr/ygr, produces yellow-green cotyledons and leaves. 3. Rosette - mutant gene ros in the homozygous condition, ros/ros, results in gibberellin deficiency and leads to lack of stem elongation.

Genetics

Monohybrid Activity

Genetics Investigation Procedure

In this investigation, you and your classmates will be given the seeds from one generation of Wisconsin Fast Plants™: the first-generation offspring (F 1 ). Four days after planting, you will be able to make observations about the phenotype of the young plants. Your teacher will plant seeds from the previous generation, the mother (P 1 ) and father (P 2 ) generation. How will you distinguish whether the mutant trait you are using is inheritable?

First Generation (F 1 Hybrid)

Day 1 Follow the “Growing Instructions” and plant F 1 seeds in all four cells of your quad. Be sure to label your quad.

Your teacher will plant a quad of each of the parental seed types (wild type and mutant type) for comparison.

Day 4 to 5 Compare the F 1 plants and both parental types. Record the number of wild-type and mutant plants that you observe among the F 1 plants in a data table. Thin to the most vigorous plant in each cell.

Day 14 to 18 Pollinate plants. Gather pollen on a bee stick from one of your F 1 plants and use it to pollinate another F 1 plant (there should be two or three flowers open on most plants when you start pollinating). Pollen may be exchanged among as many of the F 1 plants as you wish (within your quad or among all plants in the class; the more, the better at this stage). Do not worry about removing the anthers from a plant being pollinated; because the wild-type RCBrs are self-incompatible , little self-pollination will occur. Be sure that pollen from the parental-type demonstration plants is not used for these pollinations.

After pollinating, insert the bee stick in the potting mix at the base of one of your plants.

Pollinate plants about 2 and 4 days later. It is best to pollinate six to eight flowers. After your last pollination, pinch or cut off all un-opened buds and shoots so that uncontrolled pollinations cannot occur.

Day 20 to 45 Continue to remove new buds and shoots for the next 2 weeks. Keep plants watered and growing for 3 weeks after you finish pollinating to allow the seeds to ripen. Dry plants and harvest seeds as described in the “Growing Instructions.” Seeds from your plants may be combined.

Genetics

Dihybrid Genetics Activity

This activity follows the same basic procedure as the monohybrid activity; however, the P 1 and P (^2) plants are homozygous for two traits, one recessive and one dominant.

There are four phenotypes used for this dihybrid genetics investigation:

• Non-Purple - (green) no purple anthocyanin pigment is expressed in the plant (anthocyaninless). The genotype for this single gene recessive mutant is anl/anl
• Purple - a pigment known as purple anthocyanin is visible on the hypocotyl. This trait is wild- type (dominant) for anthocyaninless and is referred to as ANL/ANL Note: Anthocyanin is best observed when the plants are 4–7 days old. Look for anthocyanin expression on the stems and hypocotyls, under the cotyledons, and at the leaf tips.
• Yellow Green - this genotype, ygr, when homozygous (ygr/ygr) produces a plant that is lighter green than the normal green Fast Plant
• Normal Green - this genotype is ild-type (dominant) for yellow green and is referred to as YGR

Genetics

Test Cross

The test cross is the essential cross in genetic analyses that provides the most informative indications of independent assortment or linkage between two traits being tested. In the test cross, F 1 progeny are crossed to a stock that is homozygous for the mutant alleles being examined for linkage.

The power of the test cross in linkage mapping is that the combined recombinant frequency (recombinant class count/total) is equal to genetic map units separating the two traits.

m.u.= recombinant class count/total

In testing two unlinked recessive mutants the frequency of each parental class and each of the two expected recombinant classes is 0.25. Consider recovering the recombinant mutant class from your F2 to be used as a tester.

Genetics

Put Your Results to the Test!

Put your claims to a test! Was the ratio of the phenotypes in the F 2 generation what you predicted it would be? Was it even close? A x^2 will compare your observations with your hypothesis.

The x^2 test calculates (1) the deviation between your observed numbers and your expected numbers and (2) the probability that the deviation is due to chance or that the deviation is significant. If the deviation is merely due to chance, then the results do not disprove your hypothesis. If the deviation is significant , then your results do not support your hypothesis and you reject your hypothesis. In either case, a scientist would then run more tests to see if the results were repeatable.

Genetics