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Genetic Information

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Genetic Information

Deoxyribonucleic acid, or DNA as we all know it, is a remarkable molecule that holds our genetic information. This genetic information carries the blueprint for an organism's development, its characteristics, and is the basis of inheritance - ever wondered why children share similar features to their parents? It is because of DNA!

Storage of genetic information

You can find DNA primarily in the nucleus as chromosomes, as DNA is an extremely long molecule. DNA is also found in the mitochondria and chloroplast of plants in the form of circular DNA. To make it easier to analyze DNA, we refer to short sections of DNA as genes and different versions of the same genes as alleles. It is the base sequence of these genes that we are interested in as it determines the amino acid sequence of proteins, as illustrated below in the diagram.

Base sequence of DNA and amino acid sequence of proteins, StudySmarterBase sequence of DNA and amino acid sequence of proteins

Transport of genetic information

The genetic information stored in the base sequence of genes is transferred through protein synthesis. This process requires transcription and translation and requires other molecules like RNA to be present.

This process of transferring genetic information is a little different in prokaryotic cells. Prokaryotic cells, such as bacteria, carry their genes in extrachromosomal DNA called plasmids. These are circular pieces of DNA that are transferred to other bacteria through processes called conjugation and transformation.

In the previous section, we discussed that DNA enables offspring to share similar features to their parents. So why then do children also have different features from their parents? This is where genetic variation comes in, and this describes the differences in DNA between individuals.

What is Genetic Variation?

Genetic variation explains the differences between individuals in a species caused by changes in the DNA. The main causes of this phenomenon are mutations, meiosis and random fertilization.

Mutations describe the changes to the base sequence of genes. Below, you will see an example of a section of mutated DNA. This has the ability to change an organism's characteristics; for example, a mutation in the gene coding for a moth's wing color can turn the original brown to a darker black color. Mutations can have a disadvantageous effect, an advantageous effect or no effect on an organism. When the allele is advantageous, the organism has an increased chance of survival and a phenomenon called natural selection occurs. We'll take a look at this in the next section.

Genetic Information, original and mutated dna base sequence, StudySmarterOriginal and mutated DNA sequence

Meiosis and sexual reproduction also introduce genetic variation into a population. Meiosis, a type of cell division, involves processes called crossing over and independent assortment. These describe the exchange of DNA between chromosomes and their alignment in the cell, both of which result in changes to the DNA.

All male sperm and female eggs (gametes) contain slightly different DNA (due to meiosis), and the fertilization between these gametes is a completely random process. This is great for genetic variation because it means the resulting offspring will also have its own unique set of DNA.

Natural selection

Natural selection describes the process whereby organisms that possess characteristics that improve their ability to survive will live on to reproduce. These characteristics are granted primarily through genetic mutations, which give these organisms advantageous alleles. For example, moths with a genetic mutation that grants them a darker wing color can camouflage from their prey and survive better than moths with a lighter wing color.

Predation is termed a selection pressure as it is a factor that affects the chances of an organism's survival. Availability of food and shelter are also selection pressures that drive natural selection.

Other forms of variation

Differences between individuals are not only caused by DNA changes. Environmental factors can also modify the characteristics of an organism. Different environments will have different living conditions.

For example, plants that are exposed to more sunlight have a better chance of growing larger than plants that are in the shade for most of the day.

Genetic variation and environmental variation intersect, and they both play a role in the resulting characteristics of an organism, also called the phenotype. Therefore, it is the combination of these factors which explains the variation in individuals.

How do we measure diversity in genetic variation?

The genetic variation found within a species can be quantified by:

  • Comparing the differences in the base sequence of DNA

  • Comparing the differences in the amino acid sequence of proteins

To do this, we have to extract DNA or proteins, which are then analysed.

Biodiversity describes the variation of species we see within a community. This can be quantified using species richness . Species richness measures the number of different species in a community, for example, the number of different species found in a waterfall. Another form of measurement is the index of diversity , a formula that describes the relationship between the number of different species in a community (species richness) to the number of organisms in each species (species evenness).

Genetic Information - Key takeaways

  • All genetic information is carried in DNA.
  • Genetic variation is caused by mutations, crossing over, independent assortment and random fertilization.
  • Natural selection is the process by which organisms that possess advantageous characteristics survive and reproduce. These advantageous traits are caused by genetic variation and environmental variation.
  • Diversity can be measured using species richness and the index of diversity.

Frequently Asked Questions about Genetic Information

Genetic variation is caused by mutations, meiosis and random fertilisation. Mutations are changes in the base sequence of DNA. Meiosis involves a process called crossing over, which describes the exchange of DNA between parental chromosomes. Meiosis also involves independent assortment, which is the random alignment of chromosomes in a cell before division. Fertilisation between sperm and an egg is also a random process, and this causes genetic variation as each gametic cell contains a unique set of DNA.  

Genetic information describes the DNA base sequence of genes that code for proteins.

DNA transfers genetic information during protein synthesis - transcription and translation. Transcription describes the process in which messenger RNA (mRNA) is created from DNA and is delivered to the ribosomes. Translation describes the process in which ribosomes 'read' the genetic code on the mRNA to make a chain of amino acids, resulting in a protein.

Prokaryotic cells contain structures called plasmids, which are circular molecules of DNA and can replicate independently. These plasmids can be transferred to other bacteria through conjugation and transformation.

The 3 types of genetic variation include mutations, crossing over and independent segregation. 


Mutations describe changes to the DNA base sequence. Crossing over is the exchange of genetic material between homologous chromosomes. Independent segregation involves the random alignment of non-identical chromosomes on the metaphase plate. 

Final Genetic Information Quiz

Question

Where is DNA found?

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Nucleus. Mitochondria. Chloroplast in plants.

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Where is circular DNA found?


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Mitochondria and chloroplast in plants.

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What do genes code for?


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The base sequence of genes code for the amino acid sequence of proteins.

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What are the main causes of genetic variation in organisms?


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Mutations, crossing over, independent assortment and random fertilisation.

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Both genetics and the ________  can influence an organism's phenotype.


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Environment.

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What are mutations?

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Changes to the base sequence of DNA.

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What is crossing over in meiosis?


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The exchange of DNA between chromosomes.

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What is independent assortment in meiosis?


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The random alignment of chromosomes in a cell.

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Natural selection describes the process by which organisms with _______ characteristics survive and _______.


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Answer

Advantageous. 


Reproduce.

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What are selection pressures? Give examples. 


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Selection pressures are factors that affect an organism's chances of survival. 


Examples include predation, availability of food and availability of shelter.

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What are the methods of measuring genetic diversity within a species?


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Comparing the differences in the base sequence of DNA and comparing the amino acid sequence of proteins.

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How is biodiversity quantified?


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Using species richness and index of diversity.

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What is species richness?


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The number of different species found in a community.

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What is the index of diversity?


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A formula that is used to measure diversity. The formula indicates the number of different species found in a community and the relative number of individuals of each species.

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What is the phenotype?


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The observable characteristics of an organism. This is influenced by genetic variation and environmental factors.

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How many amino acids are there in the human body?

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20 amino acids.

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What is transcription and where does it take place?

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Transcription describes the process of making a pre-mRNA molecule. This occurs inside the nucleus.

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What is the difference between introns and exons?


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Introns are non-coding regions of DNA whereas exons are coding regions of DNA.

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What kind of mRNA do eukaryotic and prokaryotic cells make?


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During transcription, eukaryotic cells make pre-mRNA while prokaryotic cells make mRNA.

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The sense strand runs ___ to ___.


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5 'to 3'.

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What is the difference between the sense strand and the antisense strand?

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The sense strand is the DNA strand containing the code for the protein. The antisense strand, also termed the template strand, is complementary to the sense strand.

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 What are the two enzymes involved in transcription? What are their functions?


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DNA helicase and RNA polymerase. 


DNA helicase unwinds DNA by breaking hydrogen bonds between complementary base pairs. 


RNA polymerase catalyses the formation of phosphodiester bonds between adjacent RNA nucleotides.

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In RNA, adenine pairs with what nucleotide?

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Uracil.

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In DNA, adenine pairs with what nucleotide?


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Thymine.

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What is mRNA splicing?


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The removal of introns from pre-mRNA in eukaryotic cells so the resulting mRNA strand contains just exons.

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What is translation and where does it take place?


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Translation describes the process of building the polypeptide chain by 'reading' the mRNA. This occurs at the ribosomes.

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What are the two most important features of tRNA?


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tRNA contains an anticodon that can bind to its complementary mRNA codon. 


tRNA contains an attachment site for an amino acid. 

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What is the main enzyme involved in translation? What is its function?

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Peptidyl transferase. This catalyses the formation of a peptide bond between amino acids using ATP.

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What is the start codon in mRNA? What amino acid does it code for?


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AUG. These codes for methionine.

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How many tRNA's can the ribosomes harbor at any given time?


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Two tRNAs.

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 What is the end product of transcription?

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pre-mRNA for eukaryotic cells. mRNA for prokaryotic cells.

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What does the mRNA contain?

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mRNA contains codons that are derived from the template strand of DNA. These codes for the protein/polypeptide to be synthesized.

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What is the main function of mRNA?


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mRNA transfers the codons for a gene from the nucleus to the ribosomes found in the cytoplasm.

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What process does pre-mRNA undergo before translation?


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pre-mRNA in eukaryotic cells undergo mRNA splicing. This is where unwanted introns are removed, catalysed by spliceosomes.

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Where does translation take place?


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Ribosomes.

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What is the main function of tRNA?


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tRNA delivers amino acids to the ribosomes to add to the polypeptide chain.

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What are the components that are common to both mRNA and tRNA?


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A phosphate group, a ribose pentose sugar and a nitrogenous base.

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What are the RNA nitrogenous bases?


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Adenine, uracil, cytosine and guanine.

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What is the structure of mRNA?


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mRNA is a short single-stranded structure that contains codons corresponding to a protein / polypeptide.

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What are the functionally important regions in tRNA? What role do these regions play?


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The anticodon loop. These bind to the complementary codons found on mRNA.


The amino acid attachment site. This is where the amino acid temporarily binds for transport. 

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What enzyme allows the binding of the correct amino acid to its corresponding tRNA?


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Aminoacyl-tRNA synthetase.

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What pentose sugar do DNA and RNA contain?


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DNA contains deoxyribose. RNA contains ribose.

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Which nucleic acid contains uracil? What is its complementary base pair?


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RNA. Uracil pairs with adenine.

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Compare the structure of mRNA and tRNA.


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mRNA is a single-stranded helical structure. tRNA is also a single-stranded structure and it is folded into a cloverleaf shape.

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mRNA contains codons while tRNA contains ______ anticodons. 


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Complementary.

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Where is linear and circular DNA located in eukaryotic cells?

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Linear DNA is found in the nucleus. Circular DNA is found in the mitochondria and chloroplast.

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Which type of cell contains introns?

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Eukaryotic cells.

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What kind of DNA is found in prokaryotic cells?


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Circular DNA.

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What bonds are found in DNA?


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Phosphodiester bonds are found between adjacent nucleotides. Hydrogen bonds are found between complementary base pairs.

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In what manner does DNA replicate?


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Answer

Semiconservatively

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