GENES
Nature of science:
Developments in scientific Research follow improvements in technology—gene sequencers are used for the sequencing of genes. (1.8)
Understandings:
• A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.
• A gene occupies a specific position on a chromosome.
• The various specific forms of a gene are alleles.
• Alleles differ from each other by one or only a few bases.
• New alleles are formed by mutation.
• The genome is the whole of the genetic information of an organism.
• The entire base sequence of human genes was sequenced in the Human Genome Project.
Applications and skills:
• Application: The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin.
• Application: Comparison of the number of genes in humans with other species.
• Skill: Use of a database to determine differences in the base sequence of a gene in two species.
Developments in scientific Research follow improvements in technology—gene sequencers are used for the sequencing of genes. (1.8)
Understandings:
• A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.
• A gene occupies a specific position on a chromosome.
• The various specific forms of a gene are alleles.
• Alleles differ from each other by one or only a few bases.
• New alleles are formed by mutation.
• The genome is the whole of the genetic information of an organism.
• The entire base sequence of human genes was sequenced in the Human Genome Project.
Applications and skills:
• Application: The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin.
• Application: Comparison of the number of genes in humans with other species.
• Skill: Use of a database to determine differences in the base sequence of a gene in two species.
genes
A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. “Heritable” means passed on from parent to offspring, and “ characteristic” refers to genetic traits such as your hair color or your blood type. The estimated 21000 genes that you possess are organized into chromosomes.
A gene is found at a particular locus on a chromosome
A gene for a specific trait occupies a corresponding place, called a locus, on a chromosome. When geneticist map out the sequences of DNA, they carefully map the locus of each sequence. When further research reveals that a particular sequence controls a certain heritable factor, the locus of the gene is noted for further reference.
The locus of the gene controls a protein called transducing that enables color vision and it is found on chromosome 1.
The locus of the gene controls a protein called transducing that enables color vision and it is found on chromosome 1.
You will recall that you possess 2 copies of each gene in your body, one from your mother and one from your father. As a result, if you could look at the locus of the transducing gene on one of the 2 copies of your first chromosome, you will find the same gene at the same locus on the other copy of chromosome 1. One copy would be the one your mother gave you and the other your father.
Alleles: version of genes
Variations or versions of a gene are called alleles. An allele is one specific form of a gene, differing from other alleles by one or few bases. The different forms of alleles allow for a single trait, such as the trait for the ability to see in color to have variants.
cystic Fibrosis
Maintaining a proper balance of fluids in the body is essential for good health. One such fluid is mucus, a thick slippery, substance used in many parts of the body, including the lungs and intestines. A gene called CFTR found on chromosome 7 plays a key role in the production of the mucus. The standard version fo this gene allows a person’s mucus-producing cells to function properly whereas an allele generated by a mutation of the CFTR gene causes cystic fibrosis. People with this condition produce abnormally excessive quantities of mucus in various organs and have difficulties to breath, among others.
One base can make a big difference
From the sections on transcription and translation of DNA, you will remember how important it is for each letter in the genetic code to be in a specific place. If one of the bases is misplaced or substituted for a different base, the results can be dramatic. As we have seen with cystic fribosis, the difference between one version of a gene and another can mean the difference between healthy organs and organs with mucus.
mutations
A mutation is a random change in genetic material. One type involves a change of the sequence of bases in DNA. If DNA replication works correctly this shouldn’t happen. But nature sometimes makes mistakes. A mutation can happen when a base is paired with the incorrect base.
Are mutations good or bad for us?
LRP5 is a gene that helps immune system cells make a certain type of protein tht acts as a receptor on their surfaces. Research indicates that this receptor is used by the human immunodeficiency virus to enfect the cells. People with a mutation of LRP5 cannot make this receptor protein on their immune system’s cells and as a result HIV cannot infect them. This means that people with a mutted allele of LRP5 are immune to HIV. Such a mutation is very rare.
A mutation that provides an individual or a species with a better chnce for survival is considered to be a beneficial mutation and ther is a good chance that it will be passed on to the next generation. In contrast the mutations that cause disease or death are detrimental muttions and they are less likely to be passed on to future generatiosn, because they decrease the chances of an individual survival. There is also neutral mutation that do not have an effect I a species survival.
When a mutation is successfully passed on from one generation to the next, it becomes a new allele: it is a new version of the original gene. This is how new alleles are produced,
A mutation that provides an individual or a species with a better chnce for survival is considered to be a beneficial mutation and ther is a good chance that it will be passed on to the next generation. In contrast the mutations that cause disease or death are detrimental muttions and they are less likely to be passed on to future generatiosn, because they decrease the chances of an individual survival. There is also neutral mutation that do not have an effect I a species survival.
When a mutation is successfully passed on from one generation to the next, it becomes a new allele: it is a new version of the original gene. This is how new alleles are produced,
A gene to help digestion
For most of our existence humans have been hunter-gatherers and our genes are generally well adapter for this lifestyle. Originally as for all mammals the only age at which we drnk milk was were when we were infacts. By the time our ancestors reached adulthood their bodies had stopped being able to digest milk, more precisely they cant break down the disaccharide in milk called factose. This continues to be the case for most of the humans today more than half of the humans has lactose intolerant.
base substitution mutation
The type of mutation that results in a single letter being changed is a called base substitution mutation. The consequence of changing one base could mean that a different aminoacids is placed in the growing polypeptide chain. This may have little or no effect on the organism, or may have a major influence on the organisms physical characteristics.
Sickle cell disease
In humans, a mutation is sometimes found in the gene that codes for haemoglobin in red blood cells. This mutation gives a differente shape to the hemoglobin molecule. The difference leads to red bloods cells that look very different from the usual flattened disc with a hollow in the middle.
The mutated red blood cell, with a characteristic served shape, made its discoverers think of a sickle. The condition results from this mutation is therefore called sickle cell disease or sickle cell anaemia.
The kind of mutation that causes sickle cells is a base substitution mutation. In this case one base is substituted for another so that the sixth codon in this sequence of hemoglobin, GAG becomes GTG. As a result during translation instead of adding glumatic acids, the valine is added instead. Because valine has a different shape and different properties compared with glumatic acid, the shape of the resulting polypeptide chain is modified.
The symptoms of the sickle cell disease are weakness, fatigue, shortness of breath Oxygen cannot be carried as efficiently by the irregularly shaped blood cells.
The mutated red blood cell, with a characteristic served shape, made its discoverers think of a sickle. The condition results from this mutation is therefore called sickle cell disease or sickle cell anaemia.
The kind of mutation that causes sickle cells is a base substitution mutation. In this case one base is substituted for another so that the sixth codon in this sequence of hemoglobin, GAG becomes GTG. As a result during translation instead of adding glumatic acids, the valine is added instead. Because valine has a different shape and different properties compared with glumatic acid, the shape of the resulting polypeptide chain is modified.
The symptoms of the sickle cell disease are weakness, fatigue, shortness of breath Oxygen cannot be carried as efficiently by the irregularly shaped blood cells.
The advantages of sickle cell disease
Although sickle cell disease is a debilitating condition, those who have it are very resisting to malaria infection Malaria is an infections disease that occurs in tropical regions. A parasite called Plasmodium is transmitted to human blood by an infected female Anopheles mosquito feeding on the bloos. The parasite attacks the person;s red blood cells and produces symptoms of high fever and chills, and can result in death.
People who have one gene that is disc-shaped cells and one sickle-shaped cells have what is called sickle cell trait. They have some sickle-shaped cells and some normal cells in their bloodstream but in most cases they do not suffer from anemia. Anaemia is the results of low red blood cells levels characterized by a paleness of skin and low energy.
People who have one gene that is disc-shaped cells and one sickle-shaped cells have what is called sickle cell trait. They have some sickle-shaped cells and some normal cells in their bloodstream but in most cases they do not suffer from anemia. Anaemia is the results of low red blood cells levels characterized by a paleness of skin and low energy.
genomes
Sequencing DNA
In order to find out which gene does what, a list must be made showing the order of all nucleotides in the DNA code. Researchers use highly specialized laboratory equipment including sequencers to locate and identify sequence of bases. The complete set of an organism’s base sequence is called its genome.
A short fragment of a sequence look like this: GTGGACCTGACTCCTGAGGAG. Each letter represents one of the 4 bases in the DNA code. This fragment contains seven codons with a total of 21 bases. Now imagine 3 billion of those letter. That is an impressive quantity of information specially considering that you can keep it all in the nucleus of a typical cell.
In order to find out which gene does what, a list must be made showing the order of all nucleotides in the DNA code. Researchers use highly specialized laboratory equipment including sequencers to locate and identify sequence of bases. The complete set of an organism’s base sequence is called its genome.
A short fragment of a sequence look like this: GTGGACCTGACTCCTGAGGAG. Each letter represents one of the 4 bases in the DNA code. This fragment contains seven codons with a total of 21 bases. Now imagine 3 billion of those letter. That is an impressive quantity of information specially considering that you can keep it all in the nucleus of a typical cell.
How do geneticists work out the complete genome?
Many steps are necessary:
- Once DNA sampe has been taken it is chooped into fragments and copies are made of the fragments.
- To determine the sequence a DNA polymerase enzyme attaches to one copy of the first fragment. Then it will start to add free nucleotides following the principle of complementary base pairing.
- Two kinds of nucleotides will be added, some free which are standard ones and others are speial dideoxynucleotide triphosphates added as DNA chain terminators, meaning when one is reached the elongation of the strand stops.
- The result is a series of new strands some dozen of bases long, others only a handful of bases long
- Now everything is ready for the sequencing: the multiple chins of varying lengths are placed in order from the longest to the shortest. This is done using a technique called gel electrophoresis.
- To recognize each letter, a laser activates the fluorescent markers on the nucleotides as they go through the process. A sensor hooked up to a computer analyzes the wavelength of the light and determines which base they are.
- The process id repeated many times. Repetitions make sure there are no mistakes.
- Once fragment 1 is done, the lab technicians must process to fragment 2, 3 and so on.
- Once DNA sampe has been taken it is chooped into fragments and copies are made of the fragments.
- To determine the sequence a DNA polymerase enzyme attaches to one copy of the first fragment. Then it will start to add free nucleotides following the principle of complementary base pairing.
- Two kinds of nucleotides will be added, some free which are standard ones and others are speial dideoxynucleotide triphosphates added as DNA chain terminators, meaning when one is reached the elongation of the strand stops.
- The result is a series of new strands some dozen of bases long, others only a handful of bases long
- Now everything is ready for the sequencing: the multiple chins of varying lengths are placed in order from the longest to the shortest. This is done using a technique called gel electrophoresis.
- To recognize each letter, a laser activates the fluorescent markers on the nucleotides as they go through the process. A sensor hooked up to a computer analyzes the wavelength of the light and determines which base they are.
- The process id repeated many times. Repetitions make sure there are no mistakes.
- Once fragment 1 is done, the lab technicians must process to fragment 2, 3 and so on.
Advantages of genomes
An advantage of using human genome is the production of new medications. This process involves:
- Find beneficial molecules that are reproduced naturally in healthy people
- Find out which gene controls the synthesis of a desirable molecule
- Copy that gene and use it as instructions to synthesize the molecule in a lab
- Distribute the beneficial therapeutic protein as a new treatment
- Find beneficial molecules that are reproduced naturally in healthy people
- Find out which gene controls the synthesis of a desirable molecule
- Copy that gene and use it as instructions to synthesize the molecule in a lab
- Distribute the beneficial therapeutic protein as a new treatment
The human genome project
In 1990 an international cooperative venture called the Human Genome project set out to sequence the complete human genome. Because the genome of an organism is a catalogue of all bases it possesses, the Human Genome Project hoped to determine the order of all bases A,T, C and G. In 2003 the project announced that it had succeeded in achieving the goal. Now scientist are working on deciphering which sequences represent genes and which genes do what. The human genome can be though use as a map that can be used to show the locus of any gene on any one of the 23 pairs of chromosomes.
International-mindedness:
• Sequencing of the human genome shows that all humans share the vast majority of their base sequences but also that there are many single nucleotide polymorphisms that contribute to human diversity.
Theory of knowledge:
• There is a link between sickle cell anemia and prevalence of malaria. How can we know whether there is a causal link in such cases or simply a correlation?
If its because of a sickle cell then the blood cells on the body of the person infected should be different than the normal ones, if they are different then the prevalence of malaria is given because of the sickle cells. If the cell bloods are normal then the prevalence to malaria is a casual link.
Aims:
• Aim 7: The use of a database to compare DNA base sequences.
• Aim 8: Ethics of patenting human genes.
GUIDANCE
Students should be able to recall one specific base substitution that causes glutamic acid to be substituted by valine as the sixth amino acid in the hemoglobin polypeptidE.
• The number of genes in a species should not be referred to as genome size as this term is used for the total amount of DNA. At least one plant and one bacterium should be included in the comparison and at least one species with more genes and one with fewer genes than a human.
• The Genbank® database can be used to search for DNA base sequences. The cytochrome C gene sequence is available for many different organisms and is of particular interest because of its use in reclassifying organisms into three domains.
• Deletions, insertions and frame shift mutations do not need to be included.