PART FISH Genetics A Teacher’s Instructions: 1) This is the Part A of a three-part (A, B and C) project about fish genetics. Even If you do not wish to complete the entire project, you may still use Part A as a stand-alone activity. 2) Activate students’ prior knowledge by asking them the following questions: “Have you ever been told that you... A) have your mother’s/father’s eyes/nose? B) look like your mother/father? C) are tall like your grandmother/grandfather? “Do you think fish look like their parents?” 3) Explain to students that they will complete a project (if you have decided to do so) about Fish Genetics. This project is separated into Parts A, B and C. This hand out contains the project details for Part A. Below is a summary of the entire project. Details for Parts B and C can be found in PartB.pdf and PartC.pdf respectively (visit http://www.gov.mb.ca/conservation/sustain/12.html). Part A: Genes, Peas! Students will learn about Mendel’s principles and genetic terminology. Part B: Square Dance (grab your partner!) Students will learn how to use Punnett squares and pedigree charts to illustrate inheritance and solve problems. Part C: Create a Fish Students will use the knowledge they gained from parts A and B to create a fish (an offspring fish from two parent fish). 4) To complete Part A, hand out pages 2 to 12 to each student. 5) Students will read the background information on pages 2 to 6. 6) Students will use the background information and references listed on page 7 to answer the questions on pages 7 to 12. 7) Assessment: you may collect the question sheets or correct them in class. Answer keys are provided on pages 13 to 15. You may also wish to display the genetics time lines around the classroom. white sucker 1 PART FISH Genetics A PART A: Genes, Peas! Objectives: 1) To be able to outline Mendel’s principles of inheritance, describing their importance to the understanding of heredity. 2) To explain what is meant by the terms heterozygous and homozygous. 3) To distinguish between genotype and phenotype and use these terms appropriately when discussing the outcomes of genetic crosses. Tasks: 1) Read pages 2 to 6. 2) Complete the questions on pages 7 to 12 (use the resources listed on page 7). Key Terms: - allele: one of two (or more) alternative forms of a gene that give rise to alternative characteristics for a specific hereditary trait (see diagram below). - chromosome: a strand of DNA that carries genes (the genetic information of an organism). Chromosomes are capable of replicating themselves with each cell division (see diagram below). - gene: a hereditary unit (made up of DNA) that occupies a specific location on a chromosome. A gene determines a particular characteristic in an organism (see diagram below). - genetics: a branch of biology that deals with heredity and variation of organisms. - genotype: the genetic makeup of an organism or a group of organisms (the actual alleles). - heredity: the transmission of characteristics from parent to offspring. - heterozygous: having 2 different alleles for a trait (e.g. Rr). - hybrid: heterozygous or mixed. - homozygous: having 2 identical alleles for a trait (e.g. RR or rr). - phenotype: the expression of characteristics for a specific trait, the observable physical or biochemical characteristics of an organism. - purebred: homozygous. Cell Gene DNA R r Alleles Nucleus Chromosomes 2 PART FISH Genetics A Background: Gregor Mendel was born in 1822. His parents farmed but were very poor; they could not afford to send Gregor to university. So, in 1843, Gregor decided to join a monastery. Monastery life afforded Mendel time for his two passions: studying and gardening. Thus, Mendel began to experiment with plant breeding. First, Mendel studied pea plants and their characteristics. He noticed several characteristics of traits in pea plants: 1) seed colour: yellow or green, 2) seed shape: round or wrinkled, 3) flower colour: white or coloured, 4) form of ripe pod: smooth or wrinkled, 5) colour of unripe pods: green or yellow, 6) position of flowers: side or end, 7) length of stem: long or short. For his first experiment, he decided to crossbreed pea plants with round and wrinkled seeds. He used purebred plants as “parent” plants. Mendel knew that the plants were purebred because he grew them over several generations and they always produced offspring with the same characteristic for the trait of seed shape. After crossing 2 purebred plants and observing the offspring (seeds), he noticed that all of the seeds were round - he could not find one wrinkled seed! Purebred Purebred Parents Round Wrinkled Offspring Round first generation He noticed that one of the characteristics (round) appeared and the other character- istic (wrinkled) disappeared. He performed experiments with characteristics of other traits and observed the same results. For example, when tall and short plants were crossed, all the offspring were tall. Mendel used the term “dominant” for the characteristic that appeared and the term “recessive” for the characteristic that did not appear. For pea plants, round seeds and tall plants (long stem) are dominant characteristics while wrinkled seeds and short plants (short stem) are recessive characteristics for stem length and seed shape traits. x = 3 PART FISH Genetics A These results sparked Mendel’s curiosity. He decided to perform another experiment which involved crossbreeding the plants from the first generation to see which character- istic would appear in the second generation offspring. Mendel discovered that the second generation offspring had both round AND wrinkled seeds! The recessive charac- teristic had somehow reappeared. Mendel noticed that the ratio of round to wrinkled seeds was 3:1. First Generation First Generation Parents Round Round Offspring Round : Wrinkled (3:1) second generation Mendel performed this experiment again with the second generation offspring and obtained the following results. Second Generation Second Generation Parents Wrinkled Wrinkled Offspring All Wrinkled third generation Second Generation Second Generation Parents Round Round Offspring Round : Wrinkled (3:1) third generation Mendel continued to conduct similar experiments. During each experiment, he chose only one trait to study. He collected data for thousands of pea plants. During the winter he analyzed the data and made some conclusions: - Since each trait can be expressed in different ways, there must be two factors (alleles) that affect the expression of the characteristics for that trait. - One of the alleles is dominant (appears in heterozygotes/hybrids) and one allele is recessive (is ‘masked’ or ‘hidden’ in heterozygotes/ hybrids) - Each individual contains two alleles (either both dominant, both recessive, or one of each) for each trait. - The alleles must come from the parents. Offspring receive one allele from each parent. 4 PART FISH Genetics A Mendel also diagramed the results. Note: R = round (dominant), r = wrinkled (recessive). RR rr Parents Purebred Round X Purebred Wrinkled RR X rr First Generation All Round Rr Rr Rr Rr Offspring Rr Rr x Rr Parents First Generation Round X First Generation Round Rr X Rr Second Generation Round : Wrinkled (3:1) RR Rr Rr rr Offspring RR Rr rR : rr Finally, Mendel formulated 3 principles of heredity: 1) Principle of Segregation: each trait is made up of two factors. Each parent provides one factor of a characteristic for a trait. Trait = shape of seed Factors = round and wrinkled 2) Principle of Dominance: in a heterozygous/hybrid pairing, the allele that is expressed in the phenotype is dominant. The allele that is not expressed is recessive. Trait = shape of seed Expressed = round or wrinkled Dominant = round Recessive = wrinkled 3) Principle of Independent Assortment: each trait is determined separately from other traits because chromosomes sort independently. The shape of the seed (a trait) does not affect the colour of the seed (another trait). 5 PART FISH Genetics A Today we use terms such as genotype, phenotype, homozygous and heterozygous when discussing genetics. Genotype refers to the genes inherited by an offspring from its parents. For example, the genotype for a pea plant with round seeds could be RR. The genotype could also be Rr (or rR). The genotype for a pea plant with wrinkled seeds would be rr. Phenotype refers to the appearance of a trait in an offspring. For example, you may see a pea plant that has round seeds but you would be unable to tell (by observation alone) what the genetic makeup (genotype) of that plant would be. Since round is dominant, it would be impossible to tell if this particular pea plant had two dominant alleles (RR), or a dominant allele and a recessive allele (Rr). The expression of a recessive characteristic for a trait is the only case where the phenotype can be used to determine the genotype. For example, if a pea plant has wrinkled seeds and it is known that wrinkled seeds is recessive, then you would know that the genotype must be rr. SEEDS ROUND WRINKLED PHENOTYPE GENOTYPE RR r R R r r r A genotype that has two like alleles is called homozygous. For example, the genotype for wrinkled seeds is homozygous because it is rr. The genotype for round seeds is homozygous only if it is RR. If the genotype for round seeds is rR or rR, then it is called heterozygous - meaning that the alleles are different. HOMOZYGOUS HETEROZYGOUS RR r r R r r R 6 PART FISH Genetics A References: History of Genetics Timeline by Jo Ann Lane. Available at: http://www.accessexcellence.org/AE/AEPC/WWC/1994/geneticstln.html Genetics in Context. Available at: http://www.esp.org/timeline/ Time line of the History of Genetics.