SB2. Students will analyze how biological traits are passed on to successive generations.


Learning Tasks



Key Terms:

Click here to download a list of key terms for this module.  




Pre-Assessment DNA and RNA

This activity is not for a grade and will not be considered as part of your course requirement. However, it will give you an idea of what you already know and topics where you need additional instruction. Please choose true or false for the following statements.


Go to the navigation bar for the course and click on QUIZZES. Choose the quiz titled Pre-Assessment DNA and RNA.


Notes: DNA (DeoxyriboNucleic Acid)

Illustration showing how DNA comprises chromosomes in the nucleus of a cell

Image source

DeoxyriboNucleic Acid

a complex molecule (polymer) found in all living things.

Animated image of DNA

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Historical Background on discovery of DNA

In 1928 scientist Frederick Griffith conducted experiments with two related strains of bacteria, one of which has a smooth coat and caused pneumonia in mice and the other with a rough coat that did not cause pneumonia. His procedure was as follows: (see illustration below)


Image detailing Griffith experiment on mice

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Griffith proposed an explanation: Transformation;  some unknown chemical component of the dead cells was used to transform the harmless rough cells into harmful smooth ones; 

Griffith's Experiment Animation

Narrated animation of Griffith's experiment


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1944  Avery, McCloud and McCarty first purified and then tested all the chemical components of the smooth bacteria with the rough ones to determine what component caused the transformation;  the only component that transformed the bacteria was DNA, but little was known about the composition or functions of DNA.

1947  Chargaff performed chemical tests on DNA and determined that there was always the same amount of Adenine as Thymine and there was always the same amount of Cytosine as Guanine.  Conclusion:  Adenine and Thymine were paired only with each other, while cytosine and Guanine were paired only with each other as well.  As a result of his findings, he proposed Chargaff's Rules, known more commonly as 'base pairing rules.' 

1952  Hershey & Chase conducted experiments to determine conclusively whether the transforming chemical components were genetic material, DNA or some type of proteins. 

Hershey and Chase used a virus, called a bacteriophage, that infects bacteria to get DNA into cells 

Since the protein coat of viruses contains sulfur, the viruses were treated with radioactive sulfur that would bind to the protein, but not DNA, and be easily detected with special equipment 

Since DNA has phosphate molecules, but not sulfur, the viruses were also treated with radioactive phosphate that would bind to the DNA but not the protein. 

After mixing the treated viruses with untreated bacteria, special techniques were used to track the location of the radioactive isotopes of sulfur and phosphate. 

Radioactive sulfur was found on the surface of bacterial cells and radioactive phosphate was found inside the bacterial cells.

Hershey and Chase concluded that it was only the genetic material, DNA, that entered cells and caused transformations. 

For a better understanding of this critical experiment, access the link below. Select the Narrated option.  After viewing, go back and try the quiz!

Hershey-Chase Experiment Animated

Screenshot of and link to narrated description of Hershey-Chase experiment  

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In 1953 James Watson, Francis Crick and Maurice Wilkins examined an amazing photograph made by Rosalind Franklin using a technique that she developed called X-ray crystallography. 

Rosalind Franklin Photo 51 that led to the discovery of the structure of DNA

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This is Franklin's photo that led to the discovery of the structure of DNA.

With what they had discovered about the composition of DNA and Franklin's photographs, Watson & Crick developed and proposed the first model for the structure of DNA. The PBS program The Secret of Photo 51 reveals more about this intriguing story.


Watson and Crick with their model of DNA

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Watson & Crick with their model


Watch the short Discovery Education video clip Double Helix: Discovery of the DNA Structure to get a better understanding of this amazing discovery.

Video source

Their model for the DNA molecule consisted of two nucleotide chains that wrap around each other to form a double spiral. This shape is called a double helix. (The picture at the top of this page represents a double helix.) 

The primary function of DNA is to:

The monomers that make up DNA and RNA are called nucleotides. A structural formula for a sample nucleotide is shown below.

Structural formula for sample nucleotide

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Each nucleotide is composed of a sugar, a nitrogen base and a phosphate group:

A Sugar: Deoxyribose - a 5-carbon sugar in DNA Ribose - a 5-carbon sugar in RNA. This sugar has more oxygen than the sugar in DNA.

A nitrogen base:

Purines - have a double ring of carbon and nitrogen atoms.

Images of purine molecules

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 Pyrimidines - have a single ring of carbon and nitrogen atoms.

Images of pryimidine molecules

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A phosphate group: - PO4

The phosphate group is attached to the sugar, and the sugar is attached to the nitrogen base 

Two nucleotides pair to form one of the "rungs" of the ladder in a DNA double helix. 

The sugar and phosphate groups form the "backbone" or outer support of the DNA ladder-like double helix.


Base-pairing Rules

These rules describe the behavior of the bases.


  1. Cytosine always bonds with guanine by forming three hydrogen bonds. (C - G)
  2. Adenine always bonds with thymine by forming two hydrogen bonds. (A - T) In the RNA nucleotide, thymine is replaced by Uracil.
  3. A pair of bases that always bond together is known as a complementary base pair.



Replication: the process of duplicating the DNA molecule.

Watch the following Teacher's Domain video animation and explanation for the process of replication. It's a fascinating narrated animation from Interactive NOVA: The Secret of Life. It shows the double helix structure of DNA and how the molecule replicates. The segment illustrates how the DNA molecule chemically "unzips" to form templates for the new strands. The presentation also explains how complementary nucleotides bind together like the rungs of a ladder.

Video source

 After watching the animation, continue with the following notes for a more detailed discussion of the process.  

The replication or duplication of DNA depends on one main idea, namely that the nitrogen bases of the nucleotides are complementary to each other on opposite sides of the molecule as shown below. 

This pairing is due to the shapes of the nucleotide bases, which allow weak hydrogen bonds to form between the complementary bases, holding the two halves of the DNA molecule together.

Image of DNA unwinding

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The double helix unwinds, unzips, and new nucleotides are added.

Replication occurs as follows:

  1. The parent DNA molecule unwinds and unzips (an enzyme called Helicase does this) exposing the two halves of the DNA molecule
  2. Each half of the parent DNA molecule serves as a template (model) for the complementary bases to be brought into their appropriate positions.
  3. Enzymes, (DNA Polymerase), attach free nucleotides to the open complementary positions.
  4. Additional enzymes, (Ligase), connect sugars to phosphates along the sides of the newly created ladder-like helix.
  5. Another enzyme checks for errors in base pair matching and corrects the majority of mistakes, which could result in mutations. A mutation is any change in the DNA.


Image of DNA replication

 Image source

An idea about DNA size:


An average cell nucleus is about 6 micrometers in diameter. The total length of the DNA in the human genome is 1.8 meters.


There are several levels of coiling and supercoiling in DNA with strands wrapped around special protein molecules called histones.


DNA Workshop

Use the information you find in the DNA Workshop to answer the questions below. Download and use this copy of the questions to collect the information you are responsible for locating. When you have completed the assignment, place your work in your notebook. You will need this information to take the DNA Workshop and Fingerprinting Assignment Check.

Here are the important ideas you will need to know:

DNA Replication:

Protein Synthesis:



Now, go to the DNA Workshop.

Screnshot of and link to the DNA Workshop

Read the questions and directions below.

Collect the answers as you work your way through the DNA Workshop web activity.

If you need a written transcript of the workshop, visit the links below:

If you would like a hardcopy/offline version of the following instructions, click here to download the DNA Workshop Activity Guide.

DNA Replication:

1. What is DNA replication?

2. In a real cell, the molecule unwinds from spools made of _____________.

3. What helps to unzip the DNA ladder?

4. What is the base pair rule?

5. How many bases are in the DNA chain?

6. What is the base sequence from top to bottom of the DNA molecule on the right?

7. What is the base sequence from top to bottom of the DNA molecule on the left?

8. Are the 2 sequences identical?

9. How many base pairs does each human chromosome contain?

10. All 46 chromosomes contain _______________ pairs.

11. Where are you in the cell during DNA replication? Nucleus or cytoplasm?


Protein Synthesis:

12. What happens during protein synthesis?

13. At this point, DNA resembles a ___________.

14. What moves up the ladder breaking the rungs?

15. What is the base pair rule for RNA?

16. What is the base sequence from the top to the bottom of the molecule?

17. Which side is the RNA molecule? How do you know?

18. In a real cell, how long would the RNA molecule be?

19. An RNA molecule transcribed from DNA is called ___________.

20. Where will the new RNA molecule go now?

 21. Where are you in the cell now?

22. What is the function of ribosomes?

23. What is a codon?

24. What is an anticodons?

25. What is attached to the tRNA molecule?

26. What is the first amino acid in this sequence?

27. What is the first codon sequence and its compliment?

28. What is the second codon sequence and its compliment (anticodon).

29. What is the name of the second amino acid in this sequence?

30. Where will the ribosome go next? 

31. What will happen to the first tRNA?

32. What is the third codon sequence and its compliment (anticodon).

33. What is the name of the third amino acid in this sequence?

34. How long is the protein now?

35. How long can the protein chain get?

36. When will protein synthesis end?

37. What will the ribosome do when the end is reached?

38. What is the correct amino acid sequence of your protein that you just made?



DNA and Ethics Discussion

Many times doctors use DNA analysis to determine if there is some concern with the health of the fetus before it is born or fully developed. They can determine to what extent the child will have problems or disabilities.

Read this short essay before answering the questions below.

"As technology continues to advance, we are constantly presented with new and innovative methods of better understanding humankind. We now have the ability to map out our DNA down to the last A, T, C, or G, trace our ancestry based on genetic similarities and with the help of genetic testing and counseling, we can even predict our own futures with reasonable accuracy. Genetic testing and counseling make it possible to better estimate any particular health risks and indicate any preventative measures that might help lessen (or eliminate) illness. However, with this movement forward in technology, we are also faced with ethical and moral dilemmas; how to effectively use information resulting from genetic testing in a fair, just, and principled manner.

Working in conjunction with biologists an doctors, genetic counselors can provide essential information to help predict potential illness in families with a history of hereditary disease. Using human tissue samples, biologists can extract and sequence DNA to determine any abnormalities, or mutations. Genetic counselors and biologists come together when analyzing this information, and as a team, they can predict with stunning accuracy susceptibility to genetic conditions, such as certain types of cancer, mental illnesses, cystic fibrosis, Down Syndrome, and other inherited diseases. Anyone with a history of disease in their family can consider working with a genetic counselor, to discuss potential health risks. Depending on the patients situation, the genetic counselor may suggest more frequent check-ups with their doctor, additional testing, drug therapy, or possible preemptive surgery.

The ethical issues of counseling are tied closely to the ethics of the very science that provides us with information in the first place. Cost, potential insurance repercussions, and the decision of what to do with the information presented can each be potential roadblocks. Counseling and testing can cost upwards of $3500.00 for those without insurance coverage. Because of the possibility of discrimination or loss of coverage some have chosen to pay the full amount of testing themselves, rather than disclose their information to insurance companies. For many who are aware of their familial histories, or have cared for family members as they suffered, the decision to take advantage of genetic information is immensely difficult." 

View the following Teacher's Domain video DNA Detective.

Video source  

Think about what you have read and what you have seen in the video. Read the questions below and be prepared to submit your response to each.

  1. Do you think that parents should be able to use science to determine whether or not an unborn child will have a genetic disorder? 
  2. Is this taking science too far? 
  3. Should taxpayer dollars be used to do additional research into detecting genetic diseases that could be determined before birth?


Discussion icon  

Post your opinions about these questions to the discussion titled DNA and Ethics. Then respond to at least two other classmates.


DNA Fingerprinting Lab


Go to the the PBS NOVA Killer's Trail: It Takes a Lickin' webpage.

Screenshot of and link to NOVA Killers Trail: It Takes a Lickin DNA Fingerprint webpage

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Use the information you find in this link to answer the questions below. If you want a hardcopy/offline version of the questions, click here to download a copy. When you are finished, place your work in your notebook.


Image of our main character Jimmy

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**Read the background information under The Crime.

Jimmy discovered that his _________ had been disturbed.

What had happened to it?

Who are the suspects?

Explain how Jimmy will discover who disturbed his belongings.


**Proceed to Part II.

Screenshot of DNA Fingerprinting Lab

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Follow the procedures (in the correct order) to complete the DNA fingerprinting. Move the icons to the appropriate places. After each step, write a description of what you did and why

Be careful! Complete the steps in the correct order because if you make a mistake, you will have to start over again.










Compare the DNA fingerprint samples. Who was the culprit?


Now, click on Science in the Courtroom at the bottom of the page.

Judge Chernoff  

Image source

What are the 4 reasons why Judge Chernoff thinks judges should be informed about DNA fingerprinting techniques?






What does Judge Chernoff think will be the biggest problem judges and the law will face?


Go the Cleared by DNA webpage to see how use of DNA fingerprinting has affected people who had been convicted and were serving jail time for the crime.  You may be surprised!

Screenshot of and link to Cleared By DNA webpage

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DNA Workshop and Fingerprinting Assignment Check

You should have your DNA Workshop and DNA Fingerprinting Lab finished and with you as you complete the assignment check.

You will have 10 minutes to complete this assignment check. 

Quiz icon

Go to the navigation bar, proceed to QUIZZES and choose the quiz entitled DNA Workshop and Fingerprinting AC.


Study Guide DNA

Answer the following questions. If you'd like a hardcopy/offline version of the study guide, click here to download them. Use your notes to help you complete the questions for this worksheet. DNA This section tells about the experiments that helped scientists discover the relationship between genes and DNA. It also describes the chemical structure of the DNA molecule.


Griffith and Transformation

1. What did Frederick Griffith want to learn about bacteria?


Avery and DNA

2. Briefly describe how Avery and his group determined which molecule was most important for transformation

3. What was the conclusion from Avery's experiments?


The Hershey-Chase Experiment

4. What is a bacteriophage

5. What results did Hershey and Chase observe? 

6. Hershey and Chase concluded that the genetic material of the bacteriophage was _________________________ .


The Structure of DNA 

7. List the three critical things that genes were known to do





8. Adenine, guanine, cytosine, and thymine are four kinds of _______________ bases in DNA. 

9. What forms the backbone of a DNA chain?

10. Is the following sentence true or false? The nucleotides must be joined together in a specific order.

11. Rosalind Franklin's work with X-ray diffraction showed that the DNA molecule is shaped like a(an)_______________________ and contains _______________ (Matching) strands. 

12. How did Watson and Crick describe the structure of DNA? 

13. Is the following sentence true or false? According to the principle of base pairing, hydrogen bonds could form only between adenine and cytosine.


Chromosomes and DNA Replication

14. Indicate the letter of the location of DNA in prokaryotic cells.

a. nucleus

b. mitochondria

c. cytoplasm

d. vacuole


15. Is the following sentence true or false? Most prokaryotes contain a single, circular DNA molecule.

16. Is the following sentence true or false? All organisms have the same number of chromosomes.

17. Is the following sentence true or false? The E. coli chromosome is longer than the diameter of an individual E. coli bacterium.


18. Indicate the letter of each sentence that is true about chromosome structure.

a. The DNA in eukaryotic cells is very loosely packed.

b. Prokaryotic cells contain more DNA than eukaryotic cells.

c. A human cell contains more than 1 meter of DNA.

d. The DNA of the smallest human chromosome is nearly 10 times as long as many bacterial chromosomes.


DNA Replication 

19. What occurs during the process of replication?

20. What occurs when a molecule of DNA is "unzipped"?

21. What is the complimentary strand of bases for a strand with the bases TACGTT?

22. Is the following sentence true or false? Each DNA molecule resulting from replication has one original strand and one new strand.



Protein Synthesis Video Clip

Protein Synthesis

Watch the following video about protein synthesis

Screenshot of and link to animated movie about protien sythesis

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Take notes as you listen!  You will need to know information from this presentation for future quizzes or tests.



Notes: Ribonucleic Acid

RNA is a copy of a gene in DNA that is responsible for delivering genetic information from the DNA in the cell nucleus to the ribosome in the cytoplasm and the completion of the process of protein synthesis (also known as translation.)  There are several distinctive differences between DNA and RNA.

RNA and DNA comparison



Its sugar molecule is ribose.

DNA has the deoxyribose sugar

Is single stranded

Is double stranded

Uses Uracil

Uses Thymine

Is smaller and leaves the nucleus

Remain in the nucleus

Has 3 basic types

There is only one kind of DNA

Is a copy of the genetic code

Is THE genetic code


Common Types of RNA:


  1. Messenger RNA - mRNA - a single uncoiled strand that transmits information from DNA to the ribosomes during protein synthesis; a sequence of three bases that codes for one amino acid is called a codon.
  2. Transfer RNA - tRNA - a single folded strand that bonds with a specific amino acid. A sequence of three bases on one end of a tRNA molecule is called an anti-codon.
  3. Ribosomal RNA - rRNA - a globular form that is the major constituent of the ribosomes.



Transcription - the process of forming a mRNA strand from a DNA strand.

Step 1: DNA Transcription

The image below is a mRNA table for determining which codons will code for each amino acid. You may download the table for offline reference as a .pdf, .rtf, or .doc file.

A detailed codon chart



Transcription of mRNA from DNA.

transcription of mRNA from DNA

Image source

Protein synthesis - the formation of proteins using information coded on DNA and carried out by RNA.

Watch the Teacher's Domain From DNA to Protein video and animation of transcription and translation at the link below. It is a narrated presentation that illustrates the process of protein synthesis, starting with chromosomal DNA inside the cell's nucleus. You'll learn how a gene is transcribed into messenger RNA and leaves the nucleus.


Now, read the rest of the notes detailing the process of translation.

Translation - the assembling of protein molecules from information encoded in mRNA.

Now watch the short Protein Synthesis video clip. Pay close attention to references to codons.

Afterward, think about what you've learned about how proteins are assembled. In what ways are RNA and DNA similar? Different?


The three essential processes involving nucleic acids are:

  • DNA duplicates itself in replication.
  • DNA produces RNA in transcription.
  • RNA produces proteins in translation.



Replication Transcription or Translation Errors can result in Mutations: any change in the DNA of an organism. Truths about mutations:

Mutations by cell type:

Mutations within chromosomes:

Deletion - a piece of a chromosome breaks off and is lost.

Image of deletion

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Inversion - a piece of a chromosome breaks off and reattaches itself in reverse order.

Image of inversion

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Translocation - a broken piece attaches to a nonhomologous chromosome.

Image of translocation

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Nondisjunction - a pair of chromosomes fail to separate during Anaphase I of meiotic cell division; results in trisomy (three of one kind in a diploid cell) or monosomy.(one of one kind in a diploid cell)

Image of nondisjunction

Image source

This karyotype shows three of the 21st chromosome; this results in the condition known as Down Syndrome


Gene mutations:

Point mutations - a change in a single nitrogen base in DNA. If the last letter is changed it may not cause a change in the amino acid (see table); however if the first letter is changed, it could result in a "nonsense" mutation;

This example shows a normal sequence:

Normal sequence of DNA


This shows what could happen if the first letter is changed:

Another sequence of DNA


The third codon now code for the Stop sequence instead of Arginine; the protein would be severely deformed. Cystic Fibrosis disease is caused by this type of mutation.

Adapted from the Wikipedia entry, Nonsense Mutation.


Frame-shift mutation - the addition or deletion of a nitrogen base, causing a shift in the sequence of codons so that the amino acid sequence is nonsense, coding for all the wrong amino acids.

This is the normal sequence:

3rd DNA sequence


This shows the deletion of the C-G pair in the DNA:

4th DNA sequence

A deletion of the C - G in the DNA here caused the first letters in the next codon to be included in this codon...all codons from here on have their first letter shifted to the previous codon and now code for different amino acids.


Mutagen: anything that causes a mutation. Some well known environmental examples are:


Here is a short video clip that covers additional information about mutations.

Video source

Transcription and Translation Interactive Animation

 Assignment icon

Go to the Teachers' Domain animated Cell Transcription and Translation presentation webpage

Screenshot of and link to Teachers Domain transcription and translation animation

Image source

Once you made it to the site, follow these instructions:



When you have completed your work, submit it to the DROPBOX titled Transcription and Translation.


DNA to Amino Acids-Translation

Go to the Finding the DNA Structure, Copying, Reading, & Controlling DNA Code webpage.

Screenshot of and link to DNA website

On the home page, select Copying the Code at the bottom of the window.

Screenshot of copy code button

Next, choose Putting it Together at the top of the window.

Screenshot of putting it together button

Watch the video clips tutorial by clicking on Transcription or Replication at the bottom left.

Screenshot of Transcription and Replication buttons

When you are ready to try your skill at transcription, select Interactive and follow the instructions.

Screenshot of Interactive button

When finished, select Reading the Code at the bottom of the window.

Screenshot of Reading the Code button

Next, select Putting it Together at the top of the window.

Screenshot of putting it together button

You may then watch the tutorial video clip or choose Interactive or Translation.

Screenshot of Interactive and Translation buttons

Afterward, complete the assignment below:

Use an mRNA Codon/Amino Acid chart to complete the following columns. Use the information given to work forward or backward to determine left and right sides of the DNA that would match the mRNA that would match the tRNA that would carry the amino acid. Remember that a mRNA code chart determines which amino acid is specified. You may download a printable version of the columns to be completed.

The RNA Codons

The Second Nucleotide

mRNA codon to Amino Acid Chart

Incomplete chart to be solved by students

Dropbox icon

When you have completed the assignment, submit it to the DROPBOX entitled DNA to Amino Acids.

RNA Study Guide

The Structure of RNA

1. List at least three main differences between RNA and DNA.





2. What is the one job in which most RNA molecules are involved?


3. Complete the table about the common types of RNA.




Carries copies of the instructions for assembling amino acids from DNA to the rest of the cell

Ribosomal RNA



Transfers each amino acid to the ribosome to help assemble proteins


Types of RNA 

4. Indicate the letter of each sentence that is true about transcription.

a. codons are composed of four amino acids

b. both sides of DNA are copied in transcription

c.  transcription begins at a start codon and ends at a stop codon

d.  transcription utilizes uracil in place of thymine

5. Proteins are made by joining _______________ into long chains called polypeptides. 

6. How can only four bases in RNA carry instructions for 20 different amino acids? 

7. What is a codon? (Hint: Click here to look back in your notes)


8.  Indicate the letter of the number of possible three-base codons.

a. 4

b. 12

c. 64

d. 128 


9. Is the following sentence true or false? All amino acids are specified by only one codon. 



10. What occurs during the process of translation? 

11. Where does translation occur? 


Genes and Proteins

12. Many proteins are____________________ , which catalyze and regulate chemical reactions. 

13. Is the following sentence true or false? Genes are the keys to almost everything that living cells do. 



14. What are mutations?  

15. Mutations that occur at a single point in the DNA sequence are ______________________ mutations.



DNA and RNA Study Guides Assignment Check

You should have your DNA and RNA study guides finished and with you as you complete this assignment check. You will have 20 minutes to complete this assignment check. 

Quiz icon

Go to the navigation bar, proceed to QUIZZES and choose the quiz titled DNA and RNA Study Guides AC


RNA Recorded Lecture Notes


The following links give you access to the audio notes provided in this unit. 

DNA audio notes:

Screenshot of and link to audio lecture notes


RNA audio notes:

Screenshot of and link to RNA audio notes


Chromosomes and Genes Activity

At the link below you will see exactly where many of the known human genes are located on each chromosome. Take a few minutes to look at several of the chromosomes. You might even find out where some of your own unique traits originated! 

Teachers' Domain Chromosome Viewer

Screenshot of and link to chromosome viewer

Image source

At about 3 billion letters long, reading and finding anything meaningful in the human genome is a daunting task. But that's just what genome researchers do. This interactive feature provides a microscopic view of some of what they've found on our 24 chromosomes, including the locations of about 200 different genes, especially those that have been associated with disease.



Before continuing on to the Unit Test, be sure the following graded items have been completed. Click on a link below to return to the page in the module containing the assignment.

discussion icon

DNA and Ethics

quiz icon

DNA Workshop and Fingerprinting AC

dropbox icon

Transcription and Translation (counts as lab)

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DNA to Amino Acids

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DNA and RNA Study Guides AC



DNA and RNA Unit Test

quiz icon

Go to the navigation bar and click on QUIZZES. Choose the selection titled DNA and RNA Unit Test.