18.104.22.168 Genes & Proteins
Explain the relationships among DNA, genes and chromosomes.
In the context of a monohybrid cross, apply the terms phenotype, genotype, allele, homozygous and heterozygous.
Describe the process of DNA replication and the role of DNA and RNA in assembling protein molecules.
MN Standard in Lay Terms
The instructions for the making and working of organisms lie in the molecule called DNA. A length of DNA that codes for one protein (or in some cases - one RNA molecule) is called a gene. DNA makes up genes which are carried on chromosomes. There are thousands of genes on each chromosome.
During a monohybrid cross which involves the crossing of one specific gene, one of which is inherited from the mother and one from the father, the following terms will be identified and applied. Phenotype is a description of the physical manifestation of the outcome of the cross. Genotype is a description of the actual combination of genes involved. Allele is one of each of the individual "different" genes involved. Homozygous refers to the condition when both of the inherited genes are identical. Heterozygous refers to the condition when the inherited genes are different.
During cell division DNA is copied in a process called replication which uses the current strand of DNA as a pattern for assembling the new strand. DNA contains the directions for making a protein. In order to make a protein, the gene which is made of DNA must be copied to RNA in a process called transcription. In eukaryotes the RNA leaves the nucleus and joins with a ribosome in the cytoplasm. fIn prokaryotes it can join with a ribosome immediately as it is transcribed. Next the RNA is used as a pattern to line up amino acids which constitute a protein in a process called translation.
Genes are sequences of DNA, are carried on chromosomes and code for one protein. For each trait organisms have two genes one of which is inherited from the mother and one from the father. In order for these genes to be inherited they must be copied through the process of replication. In order for these genes to be expressed they must be transcribed into RNA and then translated at the ribosome into protein.
MN Standard Benchmarks
22.214.171.124.1 Explain the relationships among DNA, genes and chromosomes.
126.96.36.199.2 In the context of a monohybrid cross, apply the terms phenotype, genotype, allele, homozygous and heterozygous.
188.8.131.52.3 Describe the process of DNA replication and the role of DNA and RNA in assembling protein molecules.
See this page.
Cell store and use information to guide their functions. The genetic information stored in DNA is used to direct the synthesis of the thousands of proteins that each cell requires.
In all organisms, the instructions for specifying the characteristics of the organisms are carried in DNA, a large polymer formed from subunits of four kinds (A,G,C, and T) The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular "letters") and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosomes.
AAAS Atlas: See Benchmarks below
The information passed from parents to offspring is coded in DNA molecules. pg 108
The genetic information encoded in DNA moleculces provides instructions for assembling protein molecules. The code used is virtually the same for all life forms. Before a cell divides, the instructions are duplicated so that each of the two new cells gets all the necessary information for carrying on. pg 114
Framework for K-12 Science Education
In all organisms the genetic instructions for forming species’ characteristics are carried in the chromosomes. Each chromosome consists of a single very long DNA molecule, and each gene on the chromosome is a particular segment of that DNA. The instructions for forming species’ characteristics are carried in DNA. All cells in an organism have the same genetic content, but the genes used (expressed) by the cell may be regulated in different ways. Not all DNA codes for a protein; some segments of DNA are involved in regulatory or structural functions, and some have no as-yet known function. 12LS3.A
The information passed from parents to offspring is coded in the DNA molecules that form the chromosomes. In sexual reproduction, chromosomes can sometimes swap sections during the process of meiosis (cell division), thereby creating new genetic combinations and thus more genetic variation. Although DNA replication is tightly regulated and remarkably accurate, errors do occur and result in mutations, which are also a source of genetic variation. Environmental factors can also cause mutations in genes, and viable mutations are inherited. Environmental factors also affect expression of traits, and hence affect the probability of occurrences of traits in a population. Thus the variation and distribution of traits observed depend on both genetic and environmental factors. 12LS3.B
Systems of specialized cells within organisms help them perform the essential functions of life, which involve chemical reactions that take place between different types of molecules, such as water, proteins, carbohydrates, lipids, and nucleic acids. All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. Multicellular organisms have a hierarchical structural organization, in which any one system is made up of numerous parts and is itself a component of the next level. Feedback mechanisms maintain a living system’s internal conditions within certain limits and mediate behaviors, allowing it to remain alive and functional even as external conditions change within some range. Outside that range (e.g., at a too high or too low external temperature, with too little food or water available), the organism cannot survive. Feedback mechanisms can encourage (through positive feedback) or discourage (negative feedback) what is going on inside the living system. 12LS1.A
Common Core Standards
Common Core Standards (i.e. connections with Math, Social Studies or Language Arts Standards):
Math standards can be easily incorporated into this topic.
Math 184.108.40.206 Make reasonable estimates and judgments about the accuracy of values resulting from calculations involving measurements.
Students may do statistical analysis of crosses and determine the probability of the outcome of a genetic cross.
Math 220.127.116.11. Design simple experiments and explain the impact of sampling methods, bias and the phrasing of questions asked during data collection.
This standard can be addressed with all data collection methods. Statistical analysis and graphing can be done.
Common Core Language Arts: Students can write a laboratory report in the proper form and using their knowledge of technical writing skills. Common core standards addressed:
RST.9-10.1. Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
RST.9-10.2. Determine the central ideas or conclusions of a text; trace the text's explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
RST.9-10.3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
STATISTICS - meets MCA math standards from 18.104.22.168 to 22.214.171.124 (Data Analysis and Probability)
Gene technology is over simplified . The most common misunderstanding in a study done by ASHG was that students have an incomplete understanding of the complexity of genetic technology. They do not appreciate the limitations of the technology. (American Society of Human Genetics, 2008) Reference also NSE standards 126.96.36.199.
Single genes are always the cause of traits and inherited diseases. Students do not understand that even seeming simple inheritance is actually caused by multi-gene families and complex interactions between sequences of DNA and protein. (American Society of Human genetics, 2008)
Some students think a gene is a trait or that the DNA makes proteins (Elrod n.d.) Hard to Teach Biology Concepts pg 186. Students do not understand that genes code for specific proteins and that the production of these proteins results in the traits. (Friedrishsen and Stone, 2004) pg 186 Hard to Teach Biology Concepts
All of the chromosomes of an organism are the same (carry the same genes). Although true of homologues, this is clearly not true of non-homologous chromosomes.
The teacher has previously prepared 10 different long paper strips of colorful "DNA" of about 150 nucleotides long. The students were divided into groups of three and told that they were expected to both transcribe and then translate their DNA strand as they built a protein out of beads. The students were given a RNA codon to amino acid chart. On the back table were 20 different beads of 20 different colors each of which represented a different amino acid. Each bag (with it's unique pony bead color) was labeled with the name of one amino acid.
Working in groups, the students first transcribed the DNA into RNA. Using the "key" they then translated the RNA into the appropriate amino acid sequence. Once the amino acid sequence was obtained, the students went to the table in the back and chose their beads based on which amino acid came next. They returned to their desks and compared their beads. Surprisingly the chains were of different lengths. (NOTE: The teacher had hidden STOP codons in the original strand of DNA and if the students noticed it, their strand was only about 20 amino acids long.) Students were then asked to write a paragraph in their journal describing the use of the STOP codon in translation. What is a STOP codon, what does it look like and what happens when the ribosome tries to translate it?
(Covers benchmark 188.8.131.52.3)
Suggested Labs and Activities
184.108.40.206.1 DNA model using beads and/or paper followed by isolation of DNA.
Students begin this activity learning about the essential parts of a nucleotide (phosphate, ribose, and bases). They explore the double helix structure of DNA and then construct a model of a DNA model that they have previously planned using the "pony beads" to represent the parts of the molecule. One color is for the phosphates, one for the ribose and four different colors for the bases. The students then put the molecule together using wire (see photo) and form it into a double helix. The string of base pairs should be at least 21 long.
This project could be expanded to build a model of a whole gene (or code for one protein such as hemoglobin). The size the size of the chromosome could then be estimated based on the number of genes present on any one chromosome (see diagram).
National Human Genome Research Institute (NHGRI)
by artist Darryl Leja
DNA extraction Lab: Students choose a DNA source from various fruits and liver (works best for animal DNA). They choose a ("washing agent- soap)and add 3 mls. Two mls of salt solution is added. They can choose to add baking soda or meat tenderizer). After filtering and adding alcohol, students compare the amount of DNA based on the different ingredients they used. Students research what each of the agents do in the process of DNA extraction.
220.127.116.11.2 Statistical Interpretation of chromosome crosses (meets MCA math standards from 18.104.22.168 to 22.214.171.124)
Occasionally students have difficulty with basic statistics. Since DNA crosses involve simple statistics it can be worth the time to formally learn some basic statistics. One way to do this is to look at probability in coin flipping first with one coin, then with two and finally with four coins.
Punnett squares also follow the same laws of probability and are always an interesting way to start students understanding the statistics and probability of genetic inheritance. This is most effective when students are sent home with PTC paper or given a simple "Rolling the Tongue" phenotype test. The student then make punnet squares and statistical outcomes of genetic inheritance of their own families.
126.96.36.199.2 Rebops (also for 188.8.131.52.2)
This is a simulation type laboratory in which students drop genes in order to determine the traits of "marshmallow" animals that they created. The traits can then be crossed from the parents to make the "baby" rebops. Not only is it a very visual representation of genetic traits and crosses but it makes for a nice snack afterwards too.
184.108.40.206.3 Refer to Vignette
Use of a "Flow Map" to diagram what happens in replication, transcription and translation.
Modeling - Use beads and paper to represent the nucleotides and amino acids and then having students manipulate them in order to simulate replication, transcription and translation.
Relevancy - Use family pedigrees involving eye color, PTC tasting and tongue rolling among other traits. Caution should be used however, in the case of non-traditional family situations.
Special speakers - If students are in the class with traits they wish to share, this can be very effective. Also consider bringing in speakers with personal or family experience.
Diseases are not specifically addressed in the test specs. However, they do represent an interesting and very visual method for learning the basics of genetic inheritance, which are in the test specs. When discussing sex chromosome abnormalities and symptoms use discretion and mindful language.
Sample for "Drop your Genes":
Outstanding video. Very visual for transcription and translation. "DNA - the secret of Life" Morehead Planetarium and Science Center at the University of North Carolina at Chapel Hill., Windfall Films, 2003.
Meet the unsung heroine behind the dicovery of DNA's double helix in NOVA's "Secret of Photo 51"
Animation of protein synthesis great animations, user friendly
Protein synthesis "Junk Words" simulation. Students act out the steps of protein synthesis instructions are at this website.
Teacher's Domain - Cell Transcription and translation
- Allele: One of a number of different forms of a gene.
- Dominant Allele: The gene that prevents or covers up the expression of another gene.
- Gene: A sequence of DNA which codes for one protein
- Genotype: Genetic makeup of an organism.
- Heterozygous: Having two different alleles for a particular gene.
- Homozygous: Having two identical alleles for a particular gene.
- Monohybrid: A cross involving only one trait.
- Nucleotide: Building block of a nucleic acid.
- Phenotype: Physical characteristics of an organism.
- Protein (polypeptide): A sequence of amino acids.
- Punnett Square: A mathematical method for determining the probability of genotypes in the offspring of known parents.
- Recessive Allele: The gene that is covered up by the dominant gene and is not expressed. (Biochemically, this gene is usually absent or mutated and no longer able to express.)
- Replication: The semiconservative process of copying the DNA molecule.
- Transcription: The enzyme controlled process of making an RNA copy of the DNA gene sequence in the nucleus.
- Translation: The process of using the sequence of codons in the mRNA to sequence and connect the amino acids as a specific protein is created.
Technology can be used in a variety of ways - biotechnology
DNA isolation - This can be done using a variety of different cell types. Calf thymus works well but so do student cheek cells, bananas and onions. Woolite is a good detergent to break the cell membrane, Meat tenderizer works well to remove protein and heat then alcohol takes the DNA out of solution. Students can then spool their findings and see what "real" DNA looks like.
Electrophoresis is a method for examining the concept of DNA fingerprinting. This process separates DNA based on the length of the molecule, the sequence (cut restriction enzymes) and the charge on the phosphates. The process uses inexpensive plasticware(like Rubbermaid or Tupperware) and food coloring to simulate the process at a fraction of the cost of using DNA kits.
Assessment of Students
Include questions designed to probe student understanding of concepts, both formative and summative.
220.127.116.11.1 (Formative) Four friends were talking about human DNA, genes and chromososomes. They each had different ideas about where these structures were found. Which do you agree with and explain why you agree. Uncovering Student Ideas in Life Science, Keeley
DNA is found on genes
Chromosomes are found on genes
Genes are found on DNA
Chromosomes are found on DNA.
18.104.22.168.2 Formative - A pet mouse had babies. Five of the babies were black and two were white. The father mouse was black. The mother mouse was white. Why were the mice different colors? Uncovering Student Ideas in Life Science, Keeley
22.214.171.124.1 (Summative) Which is more devastating to the individual; a gene abnormality involving a deletion or a chromosome abnormality involving a deletion? why?
ANSWER: A Chromosome abnormality includes many genes so a chromosome abnormality would be more devastating to the individual.
Assessment of Teachers
Questions could be used as self-reflection or in professional development sessions.
1. How have you taught this topic in the past?
Based on student responses to formative assessments would you change your teaching?
2. You are doing a dihybrid cross of two traits in fruit flies and each individual is heterozygous for both traits. However, when you actually breed the fruit flies and count the offspring of the F2 generation, you find that you do not get a classic 9:3:3:1 split. What might be the explanation for this?
ANSWER: There are many possible explainations. One may be that they may involve both genes being on the same chromosome (linkage)
3. Chromosome mutations may involve translocations. When is a translocation a problem and when it it not?
ANSWER: A translocation is a problem when it is unbalanced. In a balanced translocation, assuming it does not cut a gene in two or interfere with the spacing and regulation, all genetic material is still available. However, these individuals often have difficulty in having normal children as segregation occurs in meiosis, only ½ of their gametes will receive the full complement of homologs.
Struggling and At-Risk
Many times at-risk students have difficulty with manipulation of small objects. For this reason students have the choices of using larger objects (pony beads) to make their DNA structures rather than small seed beads. Paper models the rotate around a shish-ka-bob stick set in a small bowl of plaster of paris is also effective.
Discussing syndromes, diseases and traits that are personal to students in that they themselves possess them or they have seen them in family or friends can be a very effective way of teaching. Caution must be taken however, that no one is offended and everything is in as positive a light as possible.
Vocabulary may be especially difficult in genetics. English speakers will have words that have similar meanings such as Homo for same and Hetero for different. ELL students may not have these connections so care must be taken to work on vocabulary in a more structured way (vocabulary lists and quizzes may help). A word wall can be a great asset as students see the words on a daily basis and can add to the wall as they learn new words without losing track of the ones that came before.
When working with gifted and talent students, advanced technology such as PCR. and electrophoresis can be added. In addition they may want to explore bioinformatic websites such as NCBI (National Center for Biological Information).
Advanced and/or gifted students really enjoy the puzzle element of more complicated genetic crosses such as dihybrid crosses. Some even try crosses involving more alleles than 4.
Some of the descriptions of syndromes may include some outdated analogies such as "Mongolism" when describing Down's syndrome. These should be removed if possible and explained for what they are if not.
Some monohybrid recessive genes have their roots in particular cultures. Examples include Sickle Cell Anemia and Tay-Sacs Disease. Discussing these diseases can open up some very interesting discussions on race and cultures.
The activities involving phenotypes such as " Reebops" can be modified to include fewer numbers of chromosomes. In situations where manual dexterity is an issue, this decreases the amount of time spent in constructing chromosomes. Then more time can be spent on the concept with the confusion of so very many genes and phenotypes.
When the study of DNA can be applied to real human traits that the students share it can add an additional element of interest.
Administrators may enter the classroom to see a silent group of beaders. The students are making models of DNA and they often find it very structurally stimulating and spatially enlightening. The next day the administrator may observe students excitedly stretching out their gooey white jello DNA and examining it under a microscope, feeling it's texture, stretching it to see how long it could be without breaking and generally experiencing the protein. The discussion then continues as to the moleculur level of the DNA from a molecule perspective, the properties of DNA and the macro structure of the substance.
Parents can share family histories and traits.
Students "survey" their family members of particular traits: tongue rolling, widow's peak, PTC tasting, attached earlobes, etc. The data can be compiled in class the next day. Students will find that dominant traits are not necessary the most common in a population. However, sensitivity must be shown for students who can't get the data from their biological family. When students learn that they have Grandma's eyes and Grandpa couldn't roll his tongue either, then genetics has deep meaning.
Doing DNA extraction at home will open conversations with parents about what they learned about DNA in their high school biology. Extraction has become very easy with common kitchen items.