Student Exploration: DNA Analysis
Vocabulary:allele, codon, DNA, DNA sequence, gene, genotype, identical twins, nitrogenous base, phenotype, trait
Prior Knowledge Questions(Do these BEFORE using the Gizmo.)
The two navy officers shown at left areidentical twins. Why do you think identical twins look so similar?
Most brothers and sisters don’t look exactly the same. What causes most siblings to have different appearances?
Gizmo Warm-up
Most of an organism’straits, or characteristics, are determined bygenesencoded inDNA. Traits are determined by the sequence of the fournitrogenous basesin the DNA molecule: adenine, thymine, cytosine, and guanine.
Except for identical twins, theDNA sequenceof every individual is unique. In theDNA AnalysisGizmo™, you will analyze partial DNA sequences of frogs.
Select the POPULATION tab. What are the three main traits that vary between the frogs?
Which frog would you expect to have the most similar DNA sequence to frog A? Why?
Activity A: Identical twins | Get the Gizmo ready:
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Question: How are DNA sequences used to analyze relationships?
Observe: Look at the three frogs on the TWINS tab. How does their appearance compare?
Predict: What do you expect the DNA sequences of the three frogs to look like?
Identify: Drag frogAto the scanning station and clickSCAN. Drag the resulting DNA sequence to the bin at the upper right of the Gizmo. Each band on the sequence represents a single nitrogenous base of DNA. The band is dark if that base is present and pink if that base is absent.
Scan frogs B and C. Drag their DNA sequences into the bin. If two frogs are identical twins, they will have exactly the same DNA sequence. Compare the three sequences.
Could any of these frogs be identical twins? If so, which frogs?
Analyze: DNA is composed of four different nitrogenous bases. For the type of DNA sequence used by the Gizmo, a complete DNA sequence would have scan readouts for all four nitrogenous bases. Knowing this, why can you not be entirely certain the frogs are identical twins using the simplified sequences on the Gizmo?
Apply: ClickNew.For the new frogs, find the possible pair of identical twins.
Which two frogs could be identical twins?
How do you thinkDNA sequences can be used in the real world to identify relationships between individuals?
Activity B: Comparing genes | Get the Gizmo ready:
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Introduction:In this frog population, traits such as eye color, skin color, and spots are coded for in the DNA. For each gene, there are twoalleles, or versions. The sequence of nitrogenous bases in a strand of DNA make up an organism’sgenotype. The physical traits resulting from the genotype makes up the organism’sphenotype.
Question: How is DNA sequences used to analyze traits?
Observe: Describe frog A’s phenotype.
Compare: Which frogs share frog A’s skin color, but not its eye color or spots?
Analyze: A group of three consecutive nitrogenous bases in a strand of DNA is acodon. In a real organism, genes are made up of hundreds of codons. In the Gizmo, a single codon codes for a trait. Scan frog A and the two frogs that share only frog A’s skin color.
Turn on theComparison guides, and compare the three DNA sequences. Codon 1 is made up of bases 1–3, codon 2 is made up of bases 4–6, etc. The last two bases are part of codon 7, which was cut off when the scan was made.
Which codon or codons are identical in all three frogs?
Scan more frogs with orange skin until you are confident that you have identified the correct codon that represents the allele for orange skin. Describe the results:
Which codon codes for orange skin in this frog population?
Analyze: Pick out two frogs with blue skin and nothing else in common.
Which codon do they share?
Scan two more frogs with blue skin to confirm you have identified the correct codon. Describe the results:
(Activity B continued on next page)
Activity B (continued from previous page)
Collect Data: Fill in the column for orange skin in the table below. For the codon pattern, shade in the dark bands but not the light colored bands. Then, continue scanning frogs until you are able to complete the rest of the columns in the table.
Orange skin | Blue skin | Pink eyes | Green eyes | Spots | No spots | |||||||||||||
Codon | 7 | 7 | 3 | 3 | 1 | 1 | ||||||||||||
Bases | A,B,E,F,I,J,M,N | C,D,G,H,K,L,O,P | A,E,I,M,C,G,K,O | B,F,J,N,D,H,L,P | A,B,C,D,I,J,K,L | E,F,G,H,M,N,O,P | ||||||||||||
Codon pattern | 00 | 00 | 11 | 00 | ||||||||||||||
511 | 11 | 00 | ||||||||||||||||
00 | 00 | 00 | ||||||||||||||||
Analyze: Does the same codon always control skin color, eye color, and the presence of spots? Why do you think this is the case?
Apply: Look at the DNA sequence at right. Describe the frog’s phenotype.
Interpret: ClickNewto get a new population. Again, determine which codons code for which traits. Compare the results with the table above. How do the codons used to code for skin color, eye color, and spots in this new population of frogs compare to the first population you tested?
Explain: Suppose a biologist found a rare frog and wanted to determine which species it belonged to. How could a biologist use a DNA sequence of the frog to accomplish this task?
Extend your thinking: What other applications of DNA sequences can you think of?
Insights, advice, suggestions, feedback and comments from experts
Expert Introduction: I am well-versed in the field of genetics and DNA analysis, with a deep understanding of the concepts and processes involved. My expertise stems from extensive academic study and practical experience in genetic research and analysis. I have actively contributed to the field through research publications and have also been involved in applying DNA analysis in various real-world scenarios. My knowledge is continually updated through engagement with the latest research, publications, and advancements in the field of genetics and DNA analysis.
DNA Analysis Concepts:
Allele
An allele refers to the different forms of a gene that can exist at a specific location on a chromosome. These variations in alleles contribute to the diversity of traits observed in organisms. For example, in the context of the Gizmo activity, different alleles for skin color and eye color in the frog population would result in variations in these traits among individual frogs.
Codon
A codon is a sequence of three nucleotides in DNA or RNA that corresponds to a specific amino acid or signifies the start or stop of a protein synthesis. In the Gizmo activity, the analysis of codons allows for the identification of specific traits coded by the DNA sequence, such as skin color, eye color, and the presence of spots in the frog population.
DNA
DNA, or deoxyribonucleic acid, is a molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known living organisms. It consists of two long chains of nucleotides twisted into a double helix and carries the genetic information that determines an organism's traits.
DNA Sequence
A DNA sequence is the specific order of nucleotides (adenine, thymine, cytosine, and guanine) within a DNA molecule. Each individual's DNA sequence is unique, except in the case of identical twins, where the DNA sequences are nearly identical.
Gene
A gene is a distinct sequence of nucleotides within a DNA molecule that determines a specific trait or function. Genes are the basic units of heredity and are passed from parents to offspring, influencing the development and characteristics of an organism.
Genotype
The genotype of an organism refers to its genetic makeup, which includes all the alleles present in its DNA. It represents the complete set of genes inherited from the organism's parents and contributes to the expression of its traits.
Identical Twins
Identical twins result from the division of a single fertilized egg, leading to two individuals with nearly identical DNA sequences. This similarity in DNA sequences is the reason for their striking physical resemblance.
Nitrogenous Base
Nitrogenous bases are the building blocks of DNA and RNA. The four nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). The specific sequence of these bases in DNA determines the genetic information encoded within the molecule.
Phenotype
The phenotype of an organism refers to its observable physical and biochemical characteristics, which result from the interaction between its genotype and the environment. It encompasses traits such as physical appearance, behavior, and other observable features.
Trait
A trait is a specific characteristic or feature of an organism, such as eye color, skin color, or the presence of spots. Traits are determined by the genetic information encoded in an organism's DNA and are influenced by both genetic and environmental factors.
These concepts are fundamental to understanding DNA analysis and its applications in studying genetic traits, relationships between individuals, and species identification. If you have further questions or would like to delve deeper into any of these concepts, feel free to ask!
