BIOLOGY III - Mutation and Gene Function 1



BIOLOGY III - Mutation and Gene Function 1

In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses, or can be induced by the organism, itself, by cellular processes such as hypermutation. In multicellular organisms with dedicated reproductive cells, mutations can be subdivided into germ line mutations, which can be passed on to descendants through the reproductive cells, and somatic mutations, which involve cells outside the dedicated reproductive group and which are not usually transmitted to descendants. If the organism can reproduce asexually through mechanisms such as cuttings or budding the distinction can become blurred. For example, plants can sometimes transmit somatic mutations to their descendants asexually or sexually where flower buds develop in somatically mutated parts of plants. A new mutation that was not inherited from either parent is called a de novo mutation. The source of the mutation is unrelated to the consequence, although the consequences are related to which cells are affected.

Mutations create variation within the gene pool. Less favorable (or deleterious)

mutations can be reduced in frequency in the gene pool by natural selection, while more favorable (beneficial or advantageous) mutations may accumulate and result in adaptive evolutionary changes. For example, a butterfly may produce offspring with new mutations. The majority of these mutations will have no effect; but one might change the color of one of the butterfly's offspring, making it harder (or easier) for predators to see. If this color change is advantageous, the chance of this butterfly surviving and producing its own offspring are a little better, and over time the number of butterflies with this mutation may form a larger percentage of the population.

Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can accumulate over time due to genetic drift. It is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. Also, DNA repair mechanisms are able to mend most changes before they become permanent mutations, and many organisms have mechanisms for eliminating otherwise permanently mutated somatic cells.

Mutation is generally accepted by the scientific community as the mechanism upon which natural selection acts, providing the advantageous new traits that survive and multiply in offspring or disadvantageous traits that die out with weaker organisms.

SOURCE:

Mutation and Gene Function

1. Define genetic screening

2. Discuss three advantages and disadvantages of genetic screening

3. Define the Human Genome Project:

4. State that the Human Genome project is an international cooperative venture to sequence the complete human genome

5. Discuss two possible advantages of this project

6. Define clone

7. Outline a technique used in the cloning of farm animals

8. Discuss the ethical issues of cloning human embryos

9. Discuss the results of crop plant and animal breeding

10. Define Gene Mutation

11. Outline the difference between an insertion and a deletion

12. Explain the consequence of a base substitution mutation in relation to the process of transcription and translation (You may use the example of sickle cell anaemia)

Gene Mutation

Read the text and choose an appropriate word to complete the gaps:

Mutations are changes to the ……….sequence of the genetic material of an organism.

a. chromosome b. nucleotide c. base d. protein

Due to copying errors in the genetic material during cell ………. and by exposure to ultraviolet or ionizing radiation, chemical mutagens, or carcinogens, mutations can occur deliberately during processes such as hypermutation,

a. distinction b. division c. separation d. isolation

In multicellular organisms, mutations can be subdivided into germ line mutations, , and somatic mutations. ……………….. mutations can be passed on to descendants.

a. germ line b. somatic c. asomatic d. genetic line

Plants sometimes can transmit somatic mutations to their descendants sexually or ………

a. with union b. unsexually c.without union d. asexually

A new mutation that was not inherited from either parent is called a de ……mutation.

A. novel b. novo c. new d. anew

Mutations create variation within the gene pool. Deleterious mutations can be reduced in frequency in the gene pool by natural selection, while more beneficial mutations may accumulate and result in adaptive ………..changes.

a. evolved b. evolution c. evolutionary d. evolving

Match the types of mutation with their description: frameshift, adaptive, silence, nonsense, missence, back, neutral, point.

• ……………………. mutation is what renders mutagenesis non-random in many ways and increases the rate of beneficial mutations arising.

• ……………………. or reversion is a change in a nucleotide pair of a point-mutated DNA sequence that restores the original sequence and hence the original phenotype.

• …………………….. is a mutation caused by indels, ie. inserts or deletes a number of nucleotides that is not evenly divisible by three from a DNA sequence. Due to the triplet nature of gene expression by codons, the insertion or deletion can disrupt the reading frame, or the grouping of the codons, resulting in a completely different translation from the original. The earlier in the sequence the deletion or insertion occurs, the more altered the protein produced is.

• ………………………or non-synonymous mutations are types of point mutations where a single nucleotide is changed to cause substitution of a different amino acid. This in turn can render the resulting protein non-functional. Such mutations are responsible for diseases such as epidermolysis bullosa and sickle-cell disease.

• ……………………….. is a mutation that occurs in an amino acid codon (presumably within an mRNA molecule) which results in the use of a different, but chemically similar, amino acid. This is similar to a silent mutation, where a codon mutation may encode the same amino acid (see Wobble Hypothesis); for example, a change from AUU to AUC will still encode leucine, so no discernible change occurs.

• …………………………is a point mutation in a sequence of DNA that results in a premature stop codon.

• ……………………..or substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide. Often the term point mutation also includes insertions or deletions of a single base pair (which have more of an adverse effect on the synthesized protein due to nucleotides still being read in triplets, but in different frames- a mutation called a frameshift mutation).

• …………………..mutations are DNA mutations that do not result in a change to the amino acid sequence of a protein. They may occur in a non-coding region (outside of a gene or within an intron), or they may occur within an exon in a manner that does not alter the final amino acid sequence.

Gaucher disease as a paradigm of current issues regarding single gene mutations of humans

E Beutler, Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.

Gaucher disease is a glycolytic storage disease caused by a deficiency in activity of the catabolic enzyme glucocerebrosidase. Over 35 different mutations have been documented, including missense and nonsense point mutations, splicing mutations, deletions and insertions, a fusion gene, and examples of gene conversion. Gaucher disease is most common in the Ashkenazi Jewish population, in which just five of the mutations in this population account for 98% of the disease-producing alleles. Each of these mutations is found in the context of a single haplotype, a finding consistent with a single origin of each mutation. Although it is clear that these mutations provide a selective advantage in the Jewish population and thus constitute a balanced polymorphism, the nature of the advantage is unknown. Gaucher disease can be treated symptomatically, by administration of the missing enzyme, by allogeneic bone marrow transplantation, and potentially by gene transfer into hematopoietic stem cells. Increasing understanding of this disease has, as in other genetic disorders, created a host of social and ethical dilemmas regarding matters such as the cost of treatment for rare diseases and the advantages and disadvantages of population-targeted genetic screening.

Taking into account the points raised in the abstract, write an essay discussing the advantages and disadvantages of genetic screening. (200-250 words)

You may use some of the following words:

Genetic defects recognition identification of pregnancy complications

May prevent premature death invasion of personal privacy

epidermolysis bullosa disease sickle-cell anaemia disease

blood relatives participate in clinical trials inconclusive results

for insurance purposes insurance premiums family history

for the defective breast cancer alleles ramifications of test results

insurance discrimination social discrimination mandatory testing

breast and ovaries surgically removed the sickle cell anaemia screening

likelihood of a disease change of lifestyle kept confidential

limited to life threatening diseases family relationships change

opportunity to seek medical help stigmatization loss of employment

reduction in cancer-related mortality cost-ineffective

advantages outweigh the disadvantages a feeling of relief or anxiety

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