biology 121 lab
Mendelian Genetics – Dragon Genes In chapter one, we covered the Cell Theory and Evolution and established these as two of the basic foundations of biology. A third mainstay of modern biology is the Chromosome Theory of inheritance. The modern science of genetics traces its roots to Gregor Johann Mendel, a German-‐-‐-‐Czech Augustinian monk and scientist who studied the nature of inheritance in plants. Mendel first noted that certain traits were passed from parent to offspring in a predictable manner. Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that heredity was particulate, not acquired, and that the inheritance patterns of many traits could be explained through simple rules and ratios. The experiments that led to his well-‐known theory began with the testing of thirty-‐four varieties of the edible pea (Pisum), followed by eight years of hybridization (crossing; 1856–1863). Considering seven traits, he followed the hereditary transmission of each. The scale of the research was unprecedented, the size of his progeny populations being such that clear statistical regularities emerged. It was not simply that he noted the separate behavior of the seven traits he studied, or that there was a marked difference between the population sizes of those carrying two contrasting characters, but that they approximated to the ratio 3:1. Thus, for the trait seed color, Mendel harvested 6,022 green seeds and 2,001 yellow from his hybrid progeny, offering the most striking example among his seven traits of a predictable 3:1 ratio. Further research revealed that two-‐thirds of the larger class did not breed true, while the other third bred true. Hence, the 3:1 ratio was really constituted of three classes in a 1:2:1 ratio. His experiments led him to make two generalizations: the Law of Segregation and the Law of Independent Assortment, which later came to be known as Mendel's Laws of Inheritance. We will use dragons as a model to illustrate Mendel’s model and the exceptions to his predictions.
Introduction -‐ Dragon Genes Getting started – In the download folder locate the modern genetics folder Double click on the link. Follow each modules instructions and answer the questions in the program AND the questions on your handout. Complete all four modules: Intro & rules Meiosis Pedigree and Genes The Plates Problem
Intro & rules What do dragons look like and why? Goals • learn to use the software. • make connections between the physical traits of each dragon, the genetic make-‐-‐-‐up of each dragon, and also identify particular chromosomes, genes, and alleles. • identify male and female sex chromosomes. • learn that specific combinations of alleles produce specific traits, learn that some combinations of alleles are deadly Follow this segment in order to learn BioLogica’s Chromosome Model and its representations of chromosomes, genes and alleles. It stresses the connection between genotype and phenotype.
Step One: Introduction to the BioLogica dragons and characteristics. Step Two: Become acquainted with dragon characteristics and answer questions pertaining to on screen activities. Step Three: Become acquainted with the Chromosome model. Note the differences between male & female chromosomes. Step Four: Manipulate the dragon chromosomes in order to change the alleles and traits of dragons (remember; genotype determines phenotype). Note which traits are dominant and which are recessive.
Meiosis Why don't members of a family look more alike? Meiosis introduces gamete formation by modeling the random distribution of chromosomes. Inspect, in an enlarged window, the alleles in each gamete and choose particular gametes for fertilization to produce a dragon with a specific trait. Goals • develop an understanding of the process of meiosis. Understand meiosis as a process of reduction and
division. • manipulate the gametes in the model. • Know the stages of meiosis. • Be able to describe the main results of meiosis. Part One: Introduction to Meiosis focuses on learning to use the Meiosis Model, understanding how chromosomes and alleles participate in meiosis, and linking the Meiosis Model’s representations of gametes and chromosomes with the Chromosome Model introduced previously. The Meiosis Model simulates the process of meiosis comparable to the diagrams of the phases of meiosis found in textbooks. Part Two: Designer Dragons challenges you to create specific offspring by examining the chromosomes in the gametes of each parent and selecting those that will produce the desired phenotype in the offspring. Pedigree and Genes Now that you know how to breed dragons, let's try some selective breeding. This is the pedigree view. Use the cross tool to breed a new generation of dragons. Then breed two of the dragons from this new (F1) generation together. Repeat this as far as you wish. What do you notice about the dragons as you continue to breed more generations this way? Use the chromosome tool to examine the genes of the dragons more closely. If you had trouble answering the sex-‐ linked question above, now you can observe and compare the X and Y chromosomes. Can you find any genes that are different among the members of your F8 generation? How many generations do you have to breed until all the dragons are exactly the same? You are creating an inbred strain of dragons in the last generations of this process. Write a note describing your strain, and explain what is special about all individuals in an inbred strain of organisms. Goals • develop an understanding of how genes and chromosomes separate (principal of segregation) • develop an understanding of how these relate to one another during meiosis (principal of independent
assortment) • be able to predict the phenotype based on the genes you see as you develop your pedigree. • Be able to determine the results of different generations and the loss of fixing of certain traits.
The Plates Problem Try breeding some offspring to see what crosses between these strains produce. Does the inheritance of the plates tell you anything useful? Goals • Develop an understanding of how genes relate to one another • Gain a better understanding of linked genes and how this relates to the phenotype.