3.C Genetic Variation

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Catherine French
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3.C Genetic Variation Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to life processes. EU 3.

EU 3.D: Cells communicate by generating, transmitting and receiving chemical signals. EU 3.E: Transmission of information results in changes within and between biological systems. A.

DNA mutations can be positive, negative or neutral based on the effect or the lack of effect they have on the resulting nucleic acid or protein and the phenotypes that are conferred

1. Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context. (Remember-Mutations are the primary source of genetic variation). C.

1 3.C Genetic Variation Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to life processes. EU 3.A: Heritable information provides for continuity of life. EU 3.B: Expression of genetic information involves cellular and molecular mechanisms. EU 3.C: The processing of genetic information is imperfect and is a source of genetic variation. EU 3.D: Cells communicate by generating, transmitting and receiving chemical signals. EU 3.E: Transmission of information results in changes within and between biological systems. A. Alterations in a DNA sequence can lead to changes in the type or amount of the protein produced and the consequent phenotype. 1. DNA mutations can be positive, negative or neutral based on the effect or the lack of effect they have on the resulting nucleic acid or protein and the phenotypes that are conferred by the protein. B. Errors in DNA replication or DNA repair mechanisms, and external factors, including radiation and reactive chemicals, can cause random changes, e.g., mutations in the DNA. 1. Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context. (Remember-Mutations are the primary source of genetic variation). C. Errors in mitosis or meiosis can result in changes in phenotype. 1. Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids. [See also 3.A.2] 1

2. Changes in chromosome number often result in human disorders with developmental limitations, including Trisomy 21 (Down syndrome) and XO

Genetic changes that enhance survival and reproduction can be selected by environmental conditions. [See also 1.A.2, 1.C.3] 1.

Sickle cell disorder and heterozygote advantage (Remember- Selection results in evolutionary change.) EK 3.C.

The imperfect nature of DNA replication and repair increases variation. EK 3.C.

in prokaryotes via transformation (uptake of naked DNA), transduction (viral transmission of genetic information), conjugation (cell-to-cell

2: Biological systems have multiple processes that increase genetic variation. C.

2 2. Changes in chromosome number often result in human disorders with developmental limitations, including Trisomy 21 (Down syndrome) and XO (Turner syndrome). [See also 3.A.2, 3.A.3] D. Changes in genotype may affect phenotypes that are subject to natural selection. Genetic changes that enhance survival and reproduction can be selected by environmental conditions. [See also 1.A.2, 1.C.3] 1. Antibiotic resistance mutations 2. Pesticide resistance mutations 3. Sickle cell disorder and heterozygote advantage (Remember- Selection results in evolutionary change.) EK 3.C.2: Biological systems have multiple processes that increase genetic variation. A. The imperfect nature of DNA replication and repair increases variation. EK 3.C.2: Biological systems have multiple processes that increase genetic variation. B. The horizontal acquisitions of genetic information primarily in prokaryotes via transformation (uptake of naked DNA), transduction (viral transmission of genetic information), conjugation (cell-to-cell transfer) and transposition (movement of DNA segments within and between DNA molecules) increase variation. [See also 1.B.3] EK 3.C.2: Biological systems have multiple processes that increase genetic variation. C. Sexual reproduction in eukaryotes involving gamete formation, including crossing-over during meiosis and the random assortment of chromosomes during meiosis, and fertilization serve to increase variation. Reproduction processes that increase genetic variation are evolutionarily conserved and are shared by various organisms. [See also 1.B.1, 3.A.2, 4.C.2, 4. C3] A. Viral replication differs from other reproductive strategies and generates genetic variation via various mechanisms. [See also 1.B.3] 2

1. Viruses have highly efficient replicative

model allowing one virus to produce many

Virus replication allows for mutations to occur

RNA viruses lack replication error-checking

information if they infect the same host cell.

3 1. Viruses have highly efficient replicative capabilities that allow for rapid evolution and acquisition of new phenotypes. 2. Viruses replicate via a component assembly model allowing one virus to produce many progeny simultaneously via the lytic cycle. 3. Virus replication allows for mutations to occur through usual host pathways. 4. RNA viruses lack replication error-checking mechanisms, and thus have higher rates of mutation. 5. Related viruses can combine/recombine information if they infect the same host cell. 6. HIV is a well-studied system where the rapid evolution of a virus within the host contributes to the pathogenicity of viral infection. 3

B. The reproductive cycles of viruses facilitate transfer of genetic

Viruses transmit DNA or RNA when they infect a host cell. [See also 1.

host such as increased pathogenicity in bacteria. Gene Mutations A.

Frameshift Mutations a) Base-pair insertion or deletion b) The result

Base-pair substitutions a) Silent mutations 1) Changes to codons that

4 B. The reproductive cycles of viruses facilitate transfer of genetic information. 1. Viruses transmit DNA or RNA when they infect a host cell. [See also 1.B.3] a) Transduction in bacteria b) Transposons present in incoming DNA 2. Some viruses are able to integrate into the host DNA and establish a latent (lysogenic) infection. These latent viral END genomes can result in new properties for the host such as increased pathogenicity in bacteria. Gene Mutations A. Changes in DNA nucleotides B. Point Mutations 1. Frameshift Mutations a) Base-pair insertion or deletion b) The result is frequently a nonfunctional protein. 2. Base-pair substitutions a) Silent mutations 1) Changes to codons that have same effect 2) ACC to ACA both code threonine. Gene Mutations Gene Mutations b) Nonsense mutation 1) A change that terminates the protein 2) CAG to TAG (a stop codon) c) Missense mutation 1) A change that changes the amino acid 2) CAT to CCT incorporates proline instead of histidine Back 4

5 Replication Errors A. Ability to mutate is requirement for genetic material B. Base changes during replication are one way mutations occur. C. A mismatched nucleotide may occur once per 100,000 base pairs. DNA Repair A. Mismatch repair corrects mistakes when DNA is synthesized. B. Excision repair corrects accidental changes that occur in existing DNA. C. Incorrect base pairs that survive the proofreading process contribute to gene mutations A. Environmental substances that cause mutations. B. Common mutagens are radiation, chemical, and organic carcinogens. Mutagens Antibiotic Resitance A. Original population exposed to antibiotic. B. Individual variation allows survivors. C. Survivors create greater average resistance. Pesticide Resistance A. Original population exposed to antibiotic. B. Individual variation allows survivors. C. Survivors create greater average resistance Heterzygote Advantage A. Malaria is transmitted by Anopheles mosquito B. Plasmodium (protozoan) is vector that attacks red blood cells C. Sickle cell heterozygotes have higher reproductive success where malaria exists (balanced polymorphism) 5

6 Transposons A. Barbara McClintock (nobel prize in 1983) B. Jumping genes C. Insert and excise themselves D. Most are silent 6

Molecular Genetics Student Objectives

Molecular Genetics Student Objectives Exam 1: Enduring understanding 3.A: Heritable information provides for continuity of life. Essential knowledge 3.A.1: DNA, and in some cases RNA, is the primary source