Modern Genetics
Life Science - Middle School
Chromosomes, Genes and DNA
Multimedia Lesson
Chromosomes
Presentation
Genes
Presentation
DNA
Presentation
Overview: From DNA to Protein
Presentation
DNA Transcription: DNA to RNA
Presentation
Translation: RNA to Protein
Presentation
The Genetic Code
Presentation
Mutations
Presentation
Building DNA and RNA
Virtual Lab
Chromosome and DNA Structure
Interactive
From DNA to Protein
Interactive
Deciphering the DNA Code
Interactive
Modern Genetics
Study Guide
Modern Genetics
Quiz
Modern Genetics
Flash Cards
Modern Genetics
Worksheet
Modern Genetics
Game
Modern Genetics
Vocabulary List
How Genes Work
Flip Chart
Human Genetic Disorders
Flip Chart
Study Guide Modern Genetics
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MODERN GENETICS The Genetic Code Through the years of research with DNA it has been discovered that the main function of a gene is to regulate the production of proteins within cells. What Do Proteins Do? Proteins establish the phenotype, physical characteristics, and many other traits of a particular organism. Recall from Topic 5 that DNA is made up of 4 different nitrogen bases, Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). One gene can be made up of anywhere from a few hundred nitrogen bases to well over a million. It is the order in which the nitrogen bases are arranged down a gene that forms a specific genetic code. The specific genetic code determines the type of protein that will be produced within a cell. The genetic code is based on the number three, meaning that there are a total of three bases that code for the specific type of amino acid that needs to be produced. As we learned in Topic 4, amino acids are the building blocks of protein molecules. It is the order of the genetic code that produces specific amino acids that make up a protein. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
How Cells Make Proteins Amino acids are determined by the three nitrogen base genetic code and proteins are determined by the order of amino acid. This process is known as protein synthesis. Throughout protein synthesis, the cell reads the information that is located on the DNA and produces a very specific protein. This process takes place in the cell ribosomes that are located in the cytoplasm. As we learned in Topic 3, the chromosomes are located in the nucleus and the ribosomes are located in the cytoplasm. Before the process of protein synthesis can take place the genetic code needs to be taken from the nucleus and delivered to the cytoplasm by “messenger” otherwise known as the RNA (ribonucleic acid). RNA is different from DNA in that the RNA is made up of only half of the double helix that makes up the DNA. RNA uses the nitrogen bases Adenine (A), Guanine (G), and Cytosine (C). Thymine (T) does not appear in RNA; rather Uracil (U) is used and partners up with Adenine (A). Messenger and Transfer RNA There is more than one type of RNA. The two that we will talk about are the messenger RNA (mRNA) and the transfer RNA (tRNA). Messenger RNA’s job is to copy the genetic code from the DNA in the nucleus and bring that message into the cytoplasm and attach it to the ribosome. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Transfer RNA’s job is to pick up the amino acids and attach them to the growing protein. Lesson Checkpoint: Is there one type of RNA? Mutations Mistakes occur in every process at some point. If a mistake occurs during the process of protein synthesis, it is called a mutation. A mutation is a change that takes place on a gene or a chromosome. If a mutation occurs then the cell will make the wrong protein during protein synthesis. This does not sound to be of any concern, but a single mutation of a nitrogen base can cause a drastic change in the phenotype of an organism. Other mutations could be the failure of chromosomal separation during meiosis. This can leave a cell with too few or too many chromosomes. Are mutations good or bad? Mutations can be helpful, harmful or neither. • A mutation is helpful when it increases an organism’s ability to survive and reproduce. For example, if a moth lives in a dark environment and its phenotype mutates to blend in with environment so that it can hide from predators more effectively. • A mutation is harmful when it decreases an organism’s ability to survive and reproduce. For example, if a moth lived in a dark environment and its phenotype mutates and makes it more noticeable by lightening its color against its environment. The organism’s predators will be able to find it easier and its survival and reproduction will decrease. Human Inheritance In his research, Gregor Mendel found that traits in pea plants are controlled by a single gene that has two different alleles. Most of the time there is a dominant and a recessive allele that is passed down to the offspring. This is also true for humans with some traits. The different alleles will generally have two drastically different phenotypes. For example, if you smile and you have dimples then you have the dominant allele for this gene. If you had the recessive allele then you would not have dimples at all. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Patterns of Inheritance Traits are also known to have multiple alleles for a single gene. If a trait has multiple alleles, then there can be three or more forms of a gene that are possible to have for a single trait. You can think of this as similar to ice cream, in that there are more than the traditional two flavors of vanilla and chocolate. A person is still only able to carry two forms of the gene in their DNA. Eye color is an example of a gene with multiple alleles. As we all know, there are more than two different human eye colors. There are a total of eight different colors that a human eye could be. The trait is controlled by multiple alleles. A trait can also be controlled by many different genes. For example, there are a large number of different phenotypes for human height. A number of genes can be involved with a trait giving it large variation spectrum. An organism’s environment can alter the genes that are being represented. A lack of nutrition can affect the height of an individual. Without the proper nutrients you may not be able to grow to the height that your DNA has determined. The Sex Chromosomes Human offspring receives two sets of 23 chromosomes (totaling 46) from their parents. Each parent supplies one sex chromosome that is within that set. The sex chromosomes will determine if the offspring is a male or a female and they are the only pair of chromosomes that do not always match. A female’s sex chromosomes match, but a male’s do not. A female will have two matching X chromosomes, while a male will have an X and a Y chromosome. The Y chromosome is a lot smaller than X chromosome. If you were to complete a Punnett square you would notice that the male sex cells determine the sex of the offspring. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Human Genetic Disorders A genetic disorder is a disorder that is caused by inheriting abnormal genes from the parents. They are caused by mutations in a person’s DNA either before or after meiosis. The following are genetic disorders and how they are passed to offspring: Cystic fibrosis – recessive allele Sickle-cell disease – carried on a co-dominant allele with the normal allele Hemophilia - carried on a recessive X sex chromosome Huntington’s disease – dominant allele Down syndrome – extra copy of chromosome 21 Doctors are able to diagnose genetic disorders by using amniocentesis and karyotype. An amniocentesis is a procedure that a doctor uses to take some of the fluid that surrounds a fetus while still in the womb. This allows the doctors to create a karyotype. What Is a Karyotype? A karyotype is a picture of the actual chromosomes of the organism. It can be used to see if there is a problem with the chromosomes. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Advances in Genetics Ever since the discovery of heredity and genetics people have been working to find ways to use that knowledge to develop organisms that have desirable traits. These methods are selective breeding, genetic engineering, and cloning. Selective Breeding Selective breeding is choosing organisms as the parents that have desirable traits to produce offspring. The oldest of the methods started over 5,000 years ago with the Native Americans. There was a wild grass that produced a very small amount of food. The Native Americans started saving the seeds of the plants that produced more and better food. After selectively breeding this plant species over many generations it developed into the food that is commonly known today as corn. There are two different techniques of selective breeding. Two Selective Breeding Techniques One technique is inbreeding where you breed organisms that have the same or very similar traits to produce offspring. The other technique is hybridization where you breed genetically different organisms to produce offspring. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
What is Genetic Engineering? Genetic engineering is when you transfer desirable genes into the DNA of a living organism. This method may someday be used to cure genetic disorders, make better food, and help develop better medicines. A clone is a genetically identical organism reproduced from an original organism. DNA is in every cell of every living organism and it is just as unique as the fingerprints that are on all ten of your fingers. Your DNA is different than the DNA of every other person in your school, town, state, country, and planet. DNA fingerprinting is a method used by scientists to solve crimes. If a criminal were to leave cells from their body at the crime scene like blood, hair, or skin, then the scientists can use those cells to determine a DNA fingerprint and if it was a the criminals or not. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Table Of Contents: Chromosomes, Genes and DNA
1. Chromosomes
2.1. Chromosome Location
Pairs of chromosomes are found in the nucleus of a cell. One chromosome from each pair is inherited from each parent.
2.2. Composition of Chromosomes
Chromosomes are made up of DNA (deoxyribonucleic acid), the hereditary material in humans and most other organisms.
2.3. Four Nitrogen Bases
The hereditary information in DNA is stored as a code of four nitrogen bases: adenine, guanine, cytosine, and thymine.
2.4. What Is a Gene?
Specific sections of the DNA are called genes. Each gene provides the cell with different information.
2.5. Number of Human Genes
Each chromosome is made up of many genes. There are about 100,000 genes found on human chromosomes.
2.6. Chromosome Number in Humans
In each human body cell, there are 46 chromosomes, existing in 23 pairs.
2. Genes
3.1. Function of a Gene
Each gene along a strand of DNA has the information to tell the cell to produce a specific protein.
3.2. DNA Sequence
A gene is made up of a particular sequence of DNA bases. This sequence acts as a code for a protein.
3.3. What Is a Trait?
The production of different proteins determines the traits of an organism. A trait is an inherited characteristic.
3.4. Alleles
Genes that exist in alternate forms are called alleles. The gene that determines earlobe shape exists in two alleles—one results in an attached earlobe and the other a free earlobe.
3.5. Multiple Alleles
Some genes have more than two, or multiple alleles. The human ABO blood group gene has three alleles that can combine to four types of blood groups.
3. DNA
4.1. DNA Shape and Composition
Double-stranded DNA (deoxyribonucleic acid) has a twisted ladder-like shape called a double helix. Each DNA strand is composed of a series of nucleotides.
4.2. Parts of a Nucleotide
A nucleotide contains a sugar, phosphate, and nitrogen base—adenine (A), guanine(G), cytosine(C), or thymine(T).
4.3. Complementary Base Pairs
The nitrogen bases pair with each other, adenine with thymine and cytosine with guanine. These are called complementary base pairs.
4.4. Role of DNA in Replication
The sequence of these DNA nitrogen bases provides a code. The code serves as a template when DNA is copied in a process called replication.
4.5. Role of DNA in Transcription
In a similar process called transcription, the DNA code is used to make RNA (ribonucleic acid).
4. Pause and Interact
5.1. Review
Use the whiteboard tools to complete the activity.
5.2. Chromosome and DNA Structure
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.
5. Overview: From DNA to Protein
6.1. Protein Formation
To make a protein, a gene's DNA sequence is transcribed to a strand of RNA. Then the RNA is translated into a chain of amino acids by a ribosome, and a protein is formed.
6. Pause and Interact
7.1. From DNA to Protein
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.
7. DNA Transcription: DNA to RNA
8.1. Process of Transcription
During the process of transcription a DNA gene sequence is copied to a single RNA (ribonucleic acid) strand called a messenger RNA, or mRNA.
8.2. DNA Unwinds
Transcription starts when double-stranded DNA unwinds and exposes a sequence of nitrogen bases.
8.3. Formation of RNA
A new strand of complementary bases forms to create RNA.
8.4. RNA Contains Uracil, Not Thymine
The structure of RNA is similar to DNA, but it uses the nitrogen base uracil instead of thymine.
8.5. RNA Travels to the Cytoplasm
The messenger RNA carries the code to the ribosomes in the cytoplasm.
8. Translation: RNA to Protein
9.1. What Is Translation?
The process of converting the coded information on the messenger RNA to a protein is called translation.
9.2. Messenger RNA Attaches to a Ribosome
The mRNA travels through a nuclear pore to the cytoplasm and attaches to a ribosome. The ribosome moves along the mRNA strand, translating the code.
9.3. Messenger RNA Codons
Three sequential mRNA bases form a triplet code for a particular amino acid. Each triplet is called a codon.
9.4. Transfer RNA
Another type of RNA called transfer RNA (tRNA) carries specific amino acids.
9.5. Anticodons
Every tRNA has an anticodon region that is complementary to a specific codon on the mRNA.
9.6. Amino Acid Chain
Each time a tRNA anticodon and codon pair, an amino acid is added to a chain that eventually forms a specific protein.
9.7. Transfer RNA Molecules Work Together
Many tRNA molecules and ribosomes work together at the same time along one strand mRNA.
9. The Genetic Code
10.1. What Is the Genetic Code?
The correspondence between the RNA triplets or codons and specific amino acids that are used to form a particular protein is called the genetic code.
10.2. UUC Codes for Phenylalanine
For example, the triplet code UUC on a messenger RNA always pairs with the transfer RNA that carries the amino acid phenylalanine.
10.3. Genetic Code Table
This is the Genetic Code table. Find the codon UUC by starting with the left column, then going across the top, and then down the right column. UUC corresponds to the amino acid phenylalanine.
10.4. Universal Nature of the Genetic Code
The genetic code is the same in nearly all organisms.
10. Pause and Interact
11.1. Review
Use the whiteboard tools to complete the activity.
11.2. Deciphering the DNA Code
Follow the onscreen instructions.
11. Mutations
12.1. What Is a Mutation?
A mutation is a change that occurs in a gene or chromosome that can cause incorrect or different proteins to be made and alter an organism's normal trait.
12.2. Types of Mutations
A mutation in the DNA can occur when a single base pair is changed, removed, or added. Mutations can also happen when large sections of DNA are altered.
12.3. Mutations During Meiosis
Other mutations happen when the chromosomes don't separate properly during meiosis. Sex cells can end up with more or less than the normal number of chromosomes.
12.4. Harmful and Helpful Mutations
Mutations are harmful if they decrease an organism's ability to survive or reproduce. Other mutations can be helpful. Mutations are often inherited and introduce changes in a species.
12. Vocabulary Review
13.1. Chromosomes, Genes and DNA Vocabulary Matching
Use the whiteboard tools to complete the activity.
13. Virtual Investigation
14.1. Building DNA and RNA
Before mitosis begins, a cell doubles its amount of chromosomes by replicating, or copying all of its DNA. During replication, double-stranded DNA unwinds and each strand acts as a template for a new strand. DNA transcription is a similar process except only a part of the DNA sequence is copied to form a messenger RNA (mRNA) strand. In this investigation you will build new strands of DNA and RNA using nitrogen bases, sugars and phospates to create the nucleotide sequence. Remember, during replication when you are copying DNA, you must build two new strands of DNA, but during transcription only a single strand of RNA is built. Choose Build DNA or Build RNA to begin the investigation.
14. Assessment
15.1. Chromosomes, Genes, and DNA
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