Picture from "Mendel's experiments: Figure 3," by Robert Bear et al

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1 Plant Genetics Learning Objectives: Understand the basics o genetics Understand how genetics is used in Plant Science today Learn the basics o extracting DNA Learn how to make crosses between plants and understand phenotypic and genotypic ratios Background: Genetics is a branch o biology that deals with heredity o genetic properties and variation o organisms. Gregor Johann Mendel is called the ather o genetics because he discovered how traits were inherited. Previously, heredity was regarded as a blending theory and ospring were a blended mix o both parents. Mendel was an Austrian Monk who attended the University o Vienna and studied botany. He worked with peas or eight years and looked at seven dierent traits describing seed texture and color, lower color, pod texture and color, lower position and stem length: Picture rom "Mendel's experiments: igure 3," by Robert Bear et al Mendel was the irst botanist to use math to explain his results quantitatively. He discovered principles o heredity that are the oundation or genetics today. Genetics is a powerul tool used in many dierent ields, including Plant Science. Plant scientists use genetics to create new strains o plants with traits o interest (e.g. lower color or seed

2 yield). Plant scientists also change the expression o genes to create mutants which alter biological processes and enable discovery o genes control a biological process. Understanding genetics is extremely important to understanding plants and plant unction. DNA (deoxyribonucleic acid) contains the genetic material that make up an organism. DNA is made up o two chains with dierent arrangements o nucleotides. How nucleotides are arranged determines the genetic inormation. Genes are a section o the DNA sequence that describe various traits ound in an organism. All genes are located on chromosomes, which contain the organized genetic material. Pictures rom standord.edu and warwick.ac.uk Alleles are versions o genes that occupy the same position on homologous chromosomes and express variations o a trait. When an organism has identical alleles or a speciic trait is called homozygous (ex: TT). An organism having two dierent alleles or a particular trait is called heterozygous (ex: Tt). The complete genetic make up o an organism is called a genotype, whereas the phenotype is the observable physical appearance o an organism. I an allele is dominant, then that allele o the gene masks or suppresses the expression o an alternate allele. I an allele is recessive, then that allele is masked by a dominant allele and does not appear in the heterozygous condition but rather in the homozygous condition. Example with lower color: P = Parental generation Parental genotype x Purple White lowers lowers = purple (dominant) = white (recessive) 1 generation: 1 phenotype All purple lowers

3 We can use a Punnett square to understand the genotypes and phenotypes o the ospring between two parents. Genotypes: 4 purple lowers Phenotypes: 4 purple lowers When 1 plants are crossed: x 2 generation ( x ) Genotypes: 1 purple 2 purple 1 white Phenotypes: 3 purple 1 white = purple (dominant) = white (recessive) We ultimately end up with a genotypic ratio o 1 : 2 : 1 and the phenotypic ratio is 3 purple lowers : 1 white lower. Using Punnett squares, we can predict the phenotype o the ospring. Plant breeders use genetic inormation to make combinations to improve plants. They select plants with desirable traits to be parents and cross them to create progeny with improved characteristics. Norman Borlaug is the most well-known plant breeder who won the 1970 Nobel Peace Prize or his contribution through breeding o high-yielding semi-dwar varieties o wheat and maize. He is credited or saving 1 billion people worldwide. In activity A, we are going to extract DNA rom strawberries. Strawberries are ideal to extract DNA rom because they are octoploid (have 8 o each type o chromosome in each cell). Scientists extract DNA to determine the genotypes o species they are working with. In activity B, we are going to make hybridizations between two ast plants to look at the genotypes and phenotypes o the 1 progeny. Then we are going to sel the ospring to look at the phenotypic and genotypic ratio o the 2 generation. Activity A: Extracting DNA rom Strawberries Materials: plastic bag, strawberries, dish detergent, water, salt, plastic cups, coee ilter, cold ethanol, coee stirrer

4 Procedure: 1. Remove leaves rom the strawberry 2. Place strawberries into a plastic bag, seal, and gently mash berries (this breaks the cells open) 3. In a plastic cup, mix 2 teaspoons o detergent, 1 teaspoon o salt, and ½ cup o water to create the DNA extraction buer 4. Once berries are crushed, add 2 teaspoons o the DNA extraction buer into the bag o berries (this continues to break apart proteins and dissolve cell membranes) 5. Continue to mash berries but avoid making too many bubbles 6. Place a coee ilter inside a plastic cup and pour the strawberry liquid into the coee ilter 7. Slowly pour cold ethanol into the strawberry liquid, do not stir solution (this is isolating the DNA) 8. Observe as a white cloudy substance appears in the top layer (this is DNA). 9. Pick up the DNA using the stirrer Discussion questions: 1) Why do scientists extract DNA? 2) What is so important about DNA? Activity B: Understanding genetics with Wisconsin ast Plant Hybridizations Materials: ast plant seeds, 12 small planting pots, soil, 8 labeling sticks, 6 small stakes/popsicle sticks, twisty ties, planting lat with 96 cells Procedure: 1. Obtain seeds rom the teacher 2. Plant 4 pots o each o the parents with 3 seeds per pot 3. Ater a ew days, remove 2 plants so only one plant per pot 4. Use stakes to tie up plants i needed 5. Keep parents separated 6. Once ready, cross parent A by parent B Use a paint brush and brush pollen rom the male parent onto the stigma on the emale parent. Make 4 crosses on 4 dierent lowers on each plant Remove lowers that were not crossed. Use the parent with the dominant allele as male Record the phenotypes o parents and predict phenotype o ospring 7. Once ready, harvest crossed seed (1 generation) 8. Plant 3 seeds rom the 1 generation into 4 pots 9. Once ready, sel-pollinate the 1 generation Use a paint brush and brush pollen rom another lower on the same plant

5 Pollinate 4 lowers per plant Remove lowers that were not crossed. Record the phenotype o the 1 generation 10. When the plants are ready, harvest the seed rom the 2 generation. 11. Plant the 2 generation in the planting lat with 96 cells, plant 2 seeds per cell 12. Phenotype the 2 generation ater two weeks. Calculate the phenotypic ratio Picture rom Discussion questions: 3) A monster with one eye is crossed with a monster with two eyes. All their ospring have two eyes. What trait is the trait being assessed? What trait is dominant? 4) Use the letter E or the gene or number o eyes. What would happen i you crossed these parents: EE x ee? What would be the genotype o the ospring? What would be the phenotype? 5) I you crossed the ospring monsters with each other, what would be the genotypes and phenotypes produced? How many o the new ospring would you expect to have two eyes? Glossary: Allele one o two or more alternative orms o a gene that can arise by mutation, ound on the same place on a chromosome Chromosomes threadlike structures ound in every living cell, that carries the genetic inormation in the orm o genes. DNA (deoxyribonucleic acid) a material present in all living organisms that makes up chromosomes, contains all the genetic inormation o an organism Dominant reers to an allele that is expressed when it is homozygous or heterozygous

6 Gene a unit o heredity that is transerred rom parent to ospring and determines traits o the ospring Genotype genetic makeup o an organism Genotypic ratio describes the number o times a genotype could appear in the ospring ater a cross Heterozygous having dierent alleles o one or more genes and producing gametes o dierent genotypes Homologous chromosomes a pair o chromosomes that are identical in their arrangement o genes Homozygous having identical pairs o genes or a trait, having the same alleles o genes and producing gametes o identical genotypes (ex: AA or bb). Mutant has a detectable change in the genetic material that is not commonly ound, arises rom a mutation (an alteration o the DNA sequence or chromosome o an organism). Nucleotide basic building block o DNA, orm the basic structural unit o DNA Phenotype observable properties o an organism, produced by genotype and its interaction with the environment Phenotypic ratio relative number o ospring rom a particular trait Recessive reers to an allele that is expressed when it is in the homozygous state, Trait a distinguishing characteristic that can be determined by genetics.