D1.3 Mutations and Gene editing Flashcards
[D1.3.1/ D1.3.2/ D1.3.3] Describe the 3 types of gene mutation
- Substitution: one base in the coding sequence of a gene is replaced by a different base
- Insertion: an extra nucleotide is inserted in the coding gene sequence
- Deletion: a nucleotide is removed from the coding gene sequence
Both insertion and deletion causes a frameshift mutation, which is a change in the reading frame of each codon
[D1.3.1/ D1.3.2/ D1.3.3] Describe the 3 types of substitution mutation
○ Silence mutation: substituted base develops a codon that codes for the same amino acid, therefore, the polypeptide does not change
○ Non-sense mutation: substituted base develops a stop codon
○ Mis-sense mutation: substituted base develops a codon that codes for a different amino acid, therefore, the polypeptide is changed
Sickle cell anemia is caused by this mutation
[D1.3.1/ D1.3.2/ D1.3.3] Describe single-nucleotide polymorphism
○ Single Nucleotide Polymorphism (SNP) is a variation of a single nucleotide that is present among more than 1% of the population
§ SNP can be used to predict if a gene mutation will result into the formation of specific diseases
§ Due to the degeneracy of the genetic code (multiple codons code for same amino acid), there may or may not change the amino acid
[D1.3.4] Describe the cause of gene mutation
DNA gene mutations can be caused by errors in DNA replication and by mutagens such as:
1. Radiation
○ Increases mutation rate if it has enough energy to cause chemical changes in DNA
○ Includes UV radiation, x-rays, gamma rays, cosmic rays, infrared radiation
2. Chemicals
○ Cause chemical changes in DNA
[D1.3.5] Describe the randomness of gene mutation
Mutations are random changes that occur unpredictably anywhere in the base sequence of a genome. However, some bases have a higher probability of mutating than others, depending on their position within the genome and their chemical composition. Consequences of randomness is that it is unlikely to cause a beneficial change. Thus, no natural mechanism is known for making a deliberate change to a particular base with he purpose of changing a trait.
[D1.3.6] Distinguish between mutations in germ cells vs somatic cells. Mention proto-oncogenes.
If a mutation occurs in somatic cells, the mutation is not passed to the offspring, meaning that the mutated gene is eliminated with the organism dies. When there is a mutation in the genes that control cell cycle and cell division, this mutation gene is called proto-oncogenes, which can turn into cancer causing genes.
On the other hand, mutations in germ cells is passed on to the offspring. The new allele produced by the gene mutation is inherited, leading to a genetic disease.
[D1.3.7] Explain how mutations lead to genetic variation
An allele is a variant of a gene, differing in one or more bases from other alleles of the gene. Mutation changes the base sequences of a gene, thus increasing genetic variations. Even though meiosis and sexual reproduction increase variations by generating new combination of alleles, genetic mutation is the original source of all genetic variation.
[D1.3.7] Explain how mutations lead to natural selection
Although mutations are usually harmful or neutral, mutation is still required because natural selection uses genetic variation for the evolution of species. Especially when the environment is rapidly changing, a small proportion of alleles produced by mutation would be beneficial for the adaption to new conditions.
[D1.3.8/ D1.3.7] Describe gene knockout, in reference to its purpose and how it is achieved
Gene knockout is a genetic engineering technique that includes the intentional alternation of the sequences of a gene. This technique is used to determine the function of a specific gene by making a gene inactive. There is an entire library of knockout organisms, which is an collection of organisms with specific gene sequences removed, allowing researchers to observe the phenotypic change that occur due to the deletion of the target gene.
[D1.3.8/ D1.3.9] Describe CRISPR and an application example with its ethical considerations
In earlier periods, animals such as mice were used for gene knockout, however, the introduction of CRISPR made gene knockout available to more researchers. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a section of a DNA that contains a small number of base pairs that are repeated in a cluster. Cas9 enzyme and CRISPR forms Cas9-CRISPR system, which can be used to find a target gene sequence and modify the gene. For example, it can be used to edit genes for haemoglobin if the person has sickle cell anemia. However, by using this gene editing tool, there are also ethical considerations such as to what extent the genes can be edited. Furthermore, scientists across the world use different regulatory systems when using CRISPR, which there should be an effort to harmonise the regulations when using this gene editing tool.
[D1.3.10] Distinguish conserved and highly conserved sequences. Outline a trait of conserved sequences in general and a hypothesis for the reason of conservation
Conserved sequences are identical or nearly identical across a species or a group of species. Highly conserved sequences are identical or similar over long periods of evolution. Sequences that are often conserved includes protein-coding elements, elements that are transcribed to make rRNA or tRNA, and sequences to regulate gene expression. A hypothesis for the reason of conservation is due to the functional requirement of these sequences and these remain unchanged over long periods.
[D1.3.10] Discuss hypothesis surrounding the conservation of non-coding elements
Non-coding elements are also conserved in the genomes. Although the function of these elements are widely unknown, the conservation suggests that they do have functions. However, there is an alternative hypothesis based on the study that mutation rates vary throughout the genome, that conserved non-coding elements might be in regions of the genome where there are slower rates of mutation.
