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Unlocking Life's Code: A Comprehensive Guide to Molecular Genetics and Heredity in BIOL 2, Exams of Biology

Unlocking Life's Code: A Comprehensive Guide to Molecular Genetics and Heredity in BIOL 207. Ultimate Exam Study Guide Latest Updated 2025/2026. Top Score Grade A+ Guaranteed.

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Unlocking Life's Code: A Comprehensive Guide to Molecular
Genetics and Heredity in BIOL 207.
Ultimate Exam Study Guide Latest Updated 2025/2026.
Top Score Grade A+ Guaranteed.
Typical definition of Genetics - ansThe study of genes, heredity, and genetic variation
What is a gene? - ans•Basic unit of heredity
•Sequence of DNA that codes for a product (RNA or protein) and it's regulatory regions
•Located on chromosomes
What is an allele? - ansOne of two or more versions of a gene
What is a genome? - ans•The complete set of genetic material in a cell (including
mitochondrial, chloroplast, plasmid DNA)
•Includes genes as well as non-coding DNA regions
Genes vs Traits/phenotypes - ans•Genes are inherited
•Traits/phenotype are not directly inherited
•Traits/phenotype
•Observable characteristic
•Manifest as a result of the genes an individual carries, and the environment that influences
the expression of the genes
•Heritable trait - when a particular trait can be passed genetically
Central dogma - ansDNA -> RNA -> Protein
Since all organisms are thought to have evolved from a common ancestor this implies? -
ansthe coding system for genetic information is the same in all living organisms
ATCG
Model Genetic Organisms - ansOrganisms with characteristics that make them useful for
genetic analysis
-six have been the most intensively studied genetically
Six most intensively studied organisms - ansFruit fly, E. coli (bacterium), Nematode,
Arabidopsis thaliana, house mouse, bakers yeast
Common characteristics of model organisms - ans1. Short generation time
2. Production of numerous progeny
3. The ability to carry out controlled genetic crosses
4. The ability to be reared in a laboratory environment
5. The availability of numerous genetic variants
6. An accumulated body of knowledge about their genetic systems
How have model organisms advanced our knowledge of human genetics? - ansHelped
identified that certain alleles/genes are responsibly for certain phenotypes.
Example of early genetics - ansdomestication of plants and animals
Pangenesis - ans-each part of the body contains genetic information for that particular part
-specific particles called gemmules carry info from parts of the body to the reproductive
organs (via blood) then passed to the embryo at the moment of conception
Inheritance of Acquired Characteristics / Lamarckian Inheritance - ans-traits acquired in a
person's lifetime become incorporated onto the person's hereditary info and are passed onto
offspring
ex. those who develop musical abilities may pass it done to there children
Preformationism - ans-inside egg or sperm is a tiny version of an adult (homunculus)
-this little man simple enlarges in the course of development
-offspring is genetically solely of the mother or of the father
Blending inheritance - ans-each traits of offspring are a blend or mixture of parental traits
-suggested genetic material blends like colored traits
What led to the proposal of the Weismann : Germ-plasm theory - ans-tested the idea of
acquired inheritance of acquired traits by cutting of the tails of mice for 22 generations
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Genetics and Heredity in BIOL 207.

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Typical definition of Genetics - ansThe study of genes, heredity, and genetic variation What is a gene? - ans•Basic unit of heredity •Sequence of DNA that codes for a product (RNA or protein) and it's regulatory regions •Located on chromosomes What is an allele? - ansOne of two or more versions of a gene What is a genome? - ans•The complete set of genetic material in a cell (including mitochondrial, chloroplast, plasmid DNA) •Includes genes as well as non-coding DNA regions Genes vs Traits/phenotypes - ans•Genes are inherited •Traits/phenotype are not directly inherited •Traits/phenotype •Observable characteristic •Manifest as a result of the genes an individual carries, and the environment that influences the expression of the genes •Heritable trait - when a particular trait can be passed genetically Central dogma - ansDNA - > RNA - > Protein Since all organisms are thought to have evolved from a common ancestor this implies? - ansthe coding system for genetic information is the same in all living organisms ATCG Model Genetic Organisms - ansOrganisms with characteristics that make them useful for genetic analysis

  • six have been the most intensively studied genetically Six most intensively studied organisms - ansFruit fly, E. coli (bacterium), Nematode, Arabidopsis thaliana, house mouse, bakers yeast Common characteristics of model organisms - ans1. Short generation time
  1. Production of numerous progeny
  2. The ability to carry out controlled genetic crosses
  3. The ability to be reared in a laboratory environment
  4. The availability of numerous genetic variants
  5. An accumulated body of knowledge about their genetic systems How have model organisms advanced our knowledge of human genetics? - ansHelped identified that certain alleles/genes are responsibly for certain phenotypes. Example of early genetics - ansdomestication of plants and animals Pangenesis - ans-each part of the body contains genetic information for that particular part
  • specific particles called gemmules carry info from parts of the body to the reproductive organs (via blood) then passed to the embryo at the moment of conception Inheritance of Acquired Characteristics / Lamarckian Inheritance - ans-traits acquired in a person's lifetime become incorporated onto the person's hereditary info and are passed onto offspring ex. those who develop musical abilities may pass it done to there children Preformationism - ans-inside egg or sperm is a tiny version of an adult (homunculus)
  • this little man simple enlarges in the course of development
  • offspring is genetically solely of the mother or of the father Blending inheritance - ans-each traits of offspring are a blend or mixture of parental traits
  • suggested genetic material blends like colored traits What led to the proposal of the Weismann : Germ-plasm theory - ans-tested the idea of acquired inheritance of acquired traits by cutting of the tails of mice for 22 generations

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  • this did not alter their tail length thus no evidence to support inheritance of acquired characteristics Weismann : Germ-plasm theory - anscells in reproductive organs carry a complete set of genetic info that is passed to the egg and sperm Schleiden and Schwann - ansThe Unified Cell Theory
  • Q: What are living things made of?
  • all life composed of cells and the cell is the fundamental unit of structure and function in living organisms Abiognesis - ans-cells arise spontaneously
  • disproved: cells arise only from pre-existing cells Darwin - ans-put forth the theory of evolution through natural selection
  • recognized the weakness in his theory: lack of understanding of heredity Key Ideas of Darwin - ans-variation of traits within populations
  • traits are inherited
  • offspring with traits that increase their probability of survival survive to reproduce Gregor Mendel - ans-principles of heredity
  • discovered basic principles of heredity
  • conclusions not widely known in the scientific community until 35 yrs after their publication
  • laid the foundation for our modern understanding of heredity
  • generally recognized today as the father of genetics

3 Laws of Heredity - ans1. The law of independent segregation: Each individual carries two copies of an inherited trait (e.g., alleles), which segregate equally in the following generation.

  1. The law of independent assortment: Different inherited traits sort independently of one another (e.g., pea plant height and flower colour)
  2. The law of dominance: For a trait, one allele is dominant and appears in a 3:1 ratio. Identification of dominant and recessive genes. Walther Flemming: chromosomes - ans-Examined salamander embryos
  • First to publish on the movement of chromosomes during cell division in 1879
  • Published description of mitosis
  • "Solved" the separation of chromosomes from mother to daughter cells
  • His observations that chromosomes double is significant to the later-discovered theory of inheritance Theodor Boveri & Walter Sutton - ans•Sperm and eggs contribute the same number of chromosomes •Behaviour of chromosomes during cell division (highly organized, appear the same in daughter cells, and doubles before cell division) can explain Mendel's laws of inheritance •The Boveri-Sutton Chromosome Theory: Heritable units are located on chromosomes •A heavily debated and controversial theory at the time Thomas Hunt Morgan - ans-Bred millions of Drosophila in his lab, hoping to study emergence of new traits and speciation
  • Discovered the first mutant fruit fly in 1910 with white eyes
  • Sex-linked trait (red dominant, white recessive)
  • Sex chromosomes in Drosophila are different sizes (observable)
  • Linked the heritable information for eye colour to X sex chromosome What did the studies of Thomas Hunt Morgan confirm? - ans1.Mendel's laws of inheritance

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  1. Type IIR mutated to be virulent. This was disproved by the fact the bacteria would need several generational mutation and we would then recover the bacteria type IIS. Avery, Macleod, and McCarty experiment - ansQuestion to be answered : What is the chemical nature of the transforming substance? Used the heat killed IIIS sample and mixed it with RNase (destroys RNA), Protease (destroys proteins) and DNase (destroys DNA). These were then mixed with type IIR and observed if the virulent bacteria was present or not in each solution. Conclusion of Avery, Macleod, and McCarty experiment - ansThe only solution to not contain IIIS was the one with DNase meaning that the transforming substance is DNA
  • nature of transforming principle Bacteriophage - ansA virus that infects bacteria
  • hereditary material is contained in its bulb and transferred into a bacteria to force replicate
  • the rest is made up of protiens Hershey and Chase experiment - ansQuestion to be answered : Which part of the phage (its DNA or protein) serves as the genetic material and is transmitted to phage progeny? Infected bacteria with a T2 phage that had isotope 35S (taken up in the protein) and 32P (taken up in the DNA). They were then blended (sheared off protein coats) and put in a centrifuge. The results showed in the 35S solution that the isotope was present in the fluid containing the virus coats (not in the/with the infected bacteria) and the 32P solution had the isotope present with the infected bacteria in the pellet at the bottom of the tube. Conclusion of Hershey and Chase experiment - ansDNA is the genetic material in bacteriophages Conrat and Singer experiment - ansTook two two types of a virus in tobacco leaves and mixed the RNA of one with the protein coat of the other to create hybrid viruses. These viruses were allowed to infect the tobacco and what was found was that the proteins that were produced were based off the RNA and not the protein coat. Conclusion of Conrat and Singer experiment - ans-revealed RNA is sometimes the genetic material for some viruses
  • nucleic acids encode hereditary info of organisms Who discovered the 3 dimensional shape of DNA? - ansROSALIND FRANKLIN and Watson and Crick Rosalind Franklin described in her laboratory notes that... - ans-structure of DNA as a double helix
  • implications of the complementary nucleotide base pairings for replications
  • variable sequences of DNA nucleotides allowing for coding of complex genetic info X-ray crystallography - ans-the golden standard technique to resolve the 3D structures of molecules
  • crystals of a substance are bombarded with x-rays which are diffracted and the spacing of the atoms within the crystal determines the diffraction pattern.
  • this will appear as spots on a photographic film which provides info about the structure
  • is incredibly difficult technique--takes years to work out the conditions necessary to crystalize a molecule ex. protein or DNA Properties of DNA - ans-bases are complimentary (AT & CG)
  • composed of two, nucleotide polymer antiparallel strands, phosphate sugar back bone to the outside
  • base pairs held together with hydrogen bonds on the inside -- allows separation
  • sequence of bases free to vary

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How did DNA meet the requirement for genetic info:

  1. Contains large amounts of complex info - ans-genetic instructions can be encoded in the DNA sequence
  • the only variable component of DNA How did DNA meet the requirement for genetic info:
  1. Replicate Faithfully - ans-complementary nucleotide pairs, held together with hydrogen bonds allow for replication How did DNA meet the requirement for genetic info:
  2. Encode the phenotype - ans-base sequence can be read into RNA and then from RNA into protein
  • central dogma How did DNA meet the requirement for genetic info:
  1. Have the capacity to vary - ans-differences in base sequences allow for genetic material to vary Sugars in RNA vs DNA - ansRNA has an OH bonded to the 2' C DNA has a H bonded to the 2' C Nucleotide bases in DNA and RNA - ans-purines and pyrimidines
  • purines bases only pair with pyrimidines bases in DNA A (Adenine - purine) to T (Thymine - pyrimidine) and G (Guanine - purine) to C (Cytosine - pyrimidine) in RNA A (purine) to U (Uracil - pyrimidine) and G to C
  • form hydrogen bonds Adenine and thymine pair with __ H bonds - ans Cytosine and Guanine pair with __ H bond - ans Nucleotides has a ___ group bonded to the ___ carbon of deoxyribose sugar - ansphosphate 5' What happens to the phosphate group in nucleotides during DNA synthesis - ans-phosphate group of one nucleotide is covalently bonded to the 3' carbon of deoxyribose sugar of another nucleotide DNA runs... - ans-Antiparallel.
  • 5' end phosphate to 3' end hydroxyl Exceptions to the Central Dogma - ansviruses with RNA genomes
  • one DNA molecule to another hairpin structure - ans-in single strands of nucleotides, when sequences of nucleotides on the same strand are inverted complements, a hairpin structure will be formed
  • when the complementary sequences are contiguous the hairpin has a stem but no loop
  • RNA molecules may contain numerous hairpins allowing them to fold up into complex structures RNA molecules with enzymatic activity - ansribozymes Ribozymes - ans-complex secondary structures in RNA allow it to take on catalytic activity ex. RNA splicing to alter gene expression, cleavage and ligation of RNA, DNA or proteins, ribosomes How come RNA may be considered the original genetic material? - ans-because RNA can be both genetic material as well as catalyze enzymatic rxns
  • RNA world hypothesis All DNA replication needs to be... - ans-fast and accurate

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  • leading strand vs lagging strand
  • has 3' to 5' exonuclease activity -- corrects errors
  • high processivity Elongation - Polymerase I - ans-large multiprotein complex
  • synthesizes DNA strand in 5' to 3' direction has 3' to 5' exonuclease activity
  • has 5' to 3' exonuclease activity - removes RNA primers and replace them with DNA nucleotides
  • low processivity Elongation - DNA ligase - ans-after replacement of the RNA primers, there remains a break in the DNA strand that DNA Pol I cannot fuse
  • DNA ligase does this job
  • joins okazaki fragments together to make a continuous strand of DNA Termination - ans-DNA replication ends when two replication forks meet
  • some organisms contain a specific termination sequence (Ter) that stops DNA replication Termination in E.coli - ans-in E.coli, a protein called Tus binds to Ter to terminate replication Theta replication - ansDNA replication in prokaryotes, so named because as replication proceeds around the single, circular chromosome, it takes on the appearance of the Greek letter theta.
  • double stranded DNA unwinds at origin, starts producing single stranded templates resulting in a replication bubble, fork proceeds around circle, and eventually two circular DNA molecules are produced Fidelity of DNA replication - ans-base pair error rate is <1 mistake/billion bp
  1. Errors in base pair selection by DNA polymerase =1/100,
  2. Proofreading by DNA polymerase
  3. Mismatch repair occurs soon after DNA replication How is Eukaryote DNA replication different from prokaryote? - ans-eukaryotic DNA genome is much larger
  • eukaryotic DNA associated with histones
  • eukaryotic DNA is linear Eukaryote DNA replication - Initiation - ans-thousands of origins
  • origins of replication vary in sequence
  • origin replication complex (ORC)
  • during s-phase helicase is activated
  • breaking dsDNA>ssDNA What does origin replication complex (ORC) do in replication - ans- loads complex helicase onto dsDNA (G1 stage of cell cycle Genome must be replicated.... - ansonly once ARS - ans-autonomously replicating sequences - yeast The licensing of DNA replication - ans-to make sure each piece of each chromosome is replicated once and only once per cell division in eukaryotic cells
  • ORC attaches to each origin of replication
  • MCM : minichromosomal maintenance MCM - ansminichromosomal maintenance Eukaryote DNA replication - Elongation (The DNA polymerases) - ans-DNA polymerase (has many)
  • DNA polymerase α

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DNA polymerase α - anshas primase activity and initiates nuclear DNA synthesis by synthesizing an RNA primer, followed by a short string of DNA nucleotides DNA polymerase δ - ans-DNA synthesis on lagging strand

  • delta DNA polymerase Ɛ - ans-DNA synthesis on leading strand
  • epsilon Gaps in Okazaki fragments filled by... - ansDNA polymerase δ DNA ligase function - ansseals the gaps between primer DNA and the rest of the DNA in the strand (Okazaki fragments) Eukaryote DNA replication Termination - answhen forks meet it terminates
  • there will be a section of DNA that was not replicated (overhang) How is DNA organized and condensed into chromosome? - ans-histones proteins help
  • nucleosome : 2 turns of DNA around a histone octamer
  • DNA wraps around nucleosomes with help of histones and then condense into chromosome Creation of nucleosomes requires - ans‒Disruption of original nucleosomes on the parental DNA ‒Redistribution of preexisting histones on the new DNA ‒The addition of newly synthesized histones to complete the formation of new nucleosomes Telomeres - ansRepeated DNA sequences at the ends of eukaryotic chromosomes.
  • protect the ends of DNA of chromosomes from degradation
  • associating proteins bind to the free end of DNA (G-rich 3' overhang) Sheltrin - ans(multiprotein complex)
  • binds to telomeres and prevents DNA repair mechanisms from recognizing telomere ends as a double stranded break The End-Replication Problem - ansThe inability of DNA polymerases to replicate the final segment of DNA at the 3' end of the lagging strand where there is no primer to provide a free 3'-OH group.
  • solved by circular DNA in prokaryotes Telomerase - ansAn enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.
  • elongates the ends of chromosomes
  • has specialized reverse transcriptase activity Telomerase is active in... - ans-single celled eukaryotes
  • germ cells
  • early embryonic cells
  • proliferative somatic cells (ex. bone marrow)
  • little to no activity in most stomatic cells Mice genetically engineered without telomerase showed... - ans-signs of premature aging after a few generations
  • hair loss, graying, and delayed wound healing Correlation between telomere length and longevity... - ansin zebra finches Werner syndrome - ans-autosomal recessive
  • mutation in WRN gene, which is necessary for telomere replication
  • symptoms of premature aging in adolescence/adulthood: wrinkled skin. graying hair, baldness, cataracts, muscle atrophy, cancer, osteoporosis, and heart disease cancer & telomeres - ans•Most cancer cells (90%) express telomerase

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G2 phase - ansPreparation for division; G2 /M checkpoint.

  • of chromosomes = 4

  • of DNA molecules = 8

Prophase - ansfirst and longest phase of mitosis in which the genetic material inside the nucleus condenses and the chromosomes become visible

  • Chromosomes condense and mitotic spindle forms.
  • of chromosomes = 4

  • of DNA molecules = 8

Prometaphase - ansThe second stage of mitosis, in which the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes.

  • Nuclear envelope disintegrates, and spindle microtubules anchor to kinetochores
  • of chromosomes = 4

  • of DNA molecules = 8

Metaphase - ansChromosomes line up in the middle of the cell

  • Chromosomes align on the metaphase plate; spindle-assembly checkpoint.
  • of chromosomes = 4

  • of DNA molecules = 8

Anaphase - ansPhase of mitosis in which the chromosomes separate and move to opposite ends of the cell

  • Sister chromatids separate, becoming individual chromosomes that migrate toward spindle poles.
  • of chromosomes = 8

  • of DNA molecules = 8

Telophase - ansAfter the chromosome seperates, the cell seals off, Final Phase of Mitosis.

  • Chromosomes arrive at spindle poles, the nuclear envelope re-forms, and the condensed chromosomes relax.
  • of chromosomes = 4

  • of DNA molecules = 4

Cytokinesis - ansCytoplasm divides; cell wall forms in plant cells. Order of events in M phase - ansProphase, prometaphase, metaphase, anaphase, telophase and cytokinesis Proper sister chromatid segregation depends on cohesins - ansCohesin complex (forms rings at DNA replication stage, during metaphase spindles attach to kinetochore (cohesin complex is in between the chromatids) and during anaphase Separase cleaves cohesin subunit Genetic Consequences of Mitosis - ans1.Results in 2 daughter cells that are genetically identical (in theory) 2.Results in 2 daughter cells that have the full complement of chromosomes (no increase or decrease) 3.Daughter cells contain •~half of the cytoplasm ~half of the organelles Difference between homologous pairs and sister chromatid? - ansSister chromatids are used in cell division. Sister chromatids are genetically the same homologous chromosomes are used in reproductive division 3 steps of meiosis - ansinterphase, meiosis I, meiosis II order of events in meiosis I - ansProphase I, Metaphase I, Anaphase I, and Telophase I Prophase I - ans-DNA condenses into chromosomes

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  • spindle fibers begin to form
  • homologous chromosomes pair ip
  • Some DNA arms 'crossover' swapping genetic info (chiasmata)
  • nuclear envelope disintegrates
  • 4chr, 2 pairs Metaphase I - ans-chromosomes line up in middle
  • spindle fibers attach Anaphase I - ans-two homologous pairs are separated to opposite poles Telophase I - ans-nuclear envelope begins to reform
  • spindle fibers disintegrate
  • cytokinesis begins
  • 1n, 2chr., 0 pairs of chr order of events meiosis II - ans-Prophase II, Metaphase II, Anaphase II, and Telophase II Prophase II - ans-begins to condense Metaphase II - ans-spindle fibers form and attach
  • some parts of chromosome arms swap Anaphase II - ans-sister chromatids separated and pulled to Opposite poles Telophase II - anspulls to opposite poles Begin with one cell, meiosis I ends with ___ cells and Meiosis II with ____ cells - ans2, 4 Result of meiosis II - ans-1n, 2chr., 0 pairs (per cell)
  • 4 genetically variable daughter cells Cohesion rings around chiasmata..... - anshold homologous pairs of chromosomes together Cohesion rings around centromeres... - anshold sister chromatids together Cohesion activity during metaphase I, Anaphase I, and Anaphase II - ans-MI: cohesion units still stay in contact as the chromosomes begin to pull apart
  • AI: Cohesion intis holding chromosomes together cleaves but the ones between chromatids are retained by shugoshin
  • AII: Shugoshin is degraded and the chromatids pull apart Meiosis in male animals - gametogenesis (spermatogenesis) - ans-spermatogonium may enter prophase I, becoming a primary spermatocyte or repeat mitosis (2n)
  • each primary spermatocyte completes meiosis I, producing two secondary spermatocytes (both 1n)
  • they than undergo meiosis II to produce two haploid spermatids (1n) each
  • spermatids mature into sperm then can fertilize by fusing with an ovum to produce a diploid zygote (2n) Meiosis in female animals - gametogenesis (oogenesis) - ans-oogonia in the ovaries may either undergo repeated rounds of mitosis producing additional oogonia or enter prophase I, becoming primary oocytes (2n)
  • each primary oocyte completes meiosis I, producing a large secondary oocyte and a smaller polar body, which disintegrates (1n)
  • the second oocyte completes meiosis II, producing an ovum and s second polar body, which will also disintegrate (1n)
  • then ovum will fuse with sperm to fertilize and produce a diploid zygote (2n) Genetic Consequences of Meiosis - ans1.Results in 4 daughter cells that are genetically variable 2.Results in 4 daughter cells that have half the number of chromosomes (decrease) 3.Daughter cells contain

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The importance of mutations - ans1.Necessary for Evolution: Source of all genetic variation, which further provides the raw material for evolution 2.Cause of many diseases and disorders The two basic classes of mutations in multicellular organisms - ans1.Somatic mutations 2.Germ-line mutations. Somatic Mutations - ansMutations that occur in body cells, aren't passed to offspring, and don't affect the gametes

  • reproduces in body via mitosis Germ-line mutations - ansaffect gametes; heritable and relevant to evolution Two Major Categories of Mutations - ansGene mutations Chromosomal mutations Gene mutations types - ans•Base substitutions •Insertions and Deletions •Expanding nucleotide repeats Causes of Spontaneous Base Substitutions: Spontaneous Replication Errors - ans-anomalous base-pairing arrangements
  • cytosine-adenine protonated wobble
  • thymine-guanine wobble anomalous base-pairing arrangements - ans-A tautomeric shift takes place when a proton changes its position, resulting in a rare tautomeric form.
  • Rare base tautomers cytosine-adenine protonated wobble thymine-guanine wobble - ans-Standard and anomalous base-pairing arrangements that arise if bases are in the rare tautomeric forms
  • Nonstandard base pairings can occur as a result of the flexibility in DNA structure. base substitution mutation - ansA type of mutation involving replacement or substitution of a single nucleotide base with another in DNA or RNA molecule.
  • affects only a single AA Base insertion mutation - answhen a nucleotide is added to a gene, affecting every codon from that point forward Base Deletion Mutation - answhen a nucleotide is removed from a gene, affecting every codon from that point forward Causes of Spontaneous Insertions and Deletions - ans-strand slippage
  • unequal crossing over strand slippage - ansDuring DNA replication, a mutational event leading to increased or decreased numbers of repeating nucleotides in newly synthesized DNA and caused by slippage of DNA polymerase on the template strand or slippage of the newly synthesized strand on DNA polymerase. unequal crossing over - ansMisalignment of the two DNA molecules during crossing over, resulting in one DNA molecule with an insertion and the other with a deletion Expanding nucleotide repeats - ansrepeated sequence of a set of nucleotides in which the number of copies of the sequence increases
  • Set of nucleotides that increase in copy number
  • Associated with ~30 human diseases Fragile-X Syndrome - ansA genetic disorder involving an abnormality in the X chromosome, which becomes constricted and often breaks.

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  • repeated sequence CGG Huntington's disease - ansA human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.
  • repeated sequence CAG Amyotrophic lateral sclerosis (a.k.a Lou Gehrig disease) - ansa rapidly progressive neurological disease that attacks the nerve cells responsible for controlling voluntary muscles
  • repeated sequence GGGGCC DNA is degenerate - ans- there are many possible combinations of triplets than there are amino acids Base substitutions can cause - ans(a) missense (b) nonsense(c) silent mutations missense mutation - ansA base-pair substitution that results in a codon that codes for a different amino acid. Change in AA sequence nonsense mutation - ansA mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein. silent mutation - ansA mutation that changes a single nucleotide, but does not change the amino acid created. Insertions or deletions can cause - ans(a) frameshift mutations (b) in-frame mutations (if in multiples of 3) frameshift mutations - ansmutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide in-frame mutations - ansoccur when the number of deleted or inserted base pairs IS a multiple of three. This results in a change in only a few amino acids; it may still be possible for the protein to function, even though its sequence may be slightly different. Effects of Gene Mutations on Protein Function - ans-Loss-of-function mutation •Gain-of-function mutation •Conditional mutation •Lethal mutation Loss-of-function mutation - ans•Partial or complete absence of gene product function •Usually recessive - requires two copies (in a diploid organism) to see a phenotype Gain-of-function mutation - ans•Gene product has a new function Usually dominant - one copy (in a diploid organism) produces a phenotype Conditional mutation - ansPhenotype seen under certain conditions (e.g., at elevated temperatures) Lethal mutation - ansCauses premature death Suppressor Mutations - ans•a mutation that hides or suppresses the effect of another mutation intragenic or intergenic Intragenic - ansin the same gene as original mutation Intergenic - ansin a different gene as the original mutation types of chromosomal mutations - anschromosome rearrangement, aneuploidy, polyploidy chromosome rearrangement - ansChange from the wild type in the structure of one or more chromosomes.
  • Alter the structure of chromosomes: e.g., parts of chromosomes duplicated, deleted, inverted. aneuploidy - ansAbnormal number of chromosomes.
  • Alters the number of chromosomes e.g., one or more chromosomes are added or deleted

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Robertsonian translocation - ansTranslocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, resulting in a chromosome with two long arms and usually another chromosome with two short arms. aneuploidy nondisjunction during meiosis I - ansresults in zygotes is 2 monosomic 2n- 1 and 2 trisomic 2n+ aneuploidy nondisjunction during meiosis II - ansresults in zygotes is 2 normal diploid 2n, 1 trisomic 2n+1 and 1 monosomic 2n- 1 aneuploidy nondisjunction during mitosis - anssomatic clone of monosomic cells 2n-1 and somatic clone of trisomic cells 2n+ Effects of Aneuploidy - ans•Usually lethal •No change in DNA sequence, but in copy numbers of genes - gene dosage effect •Down syndrome is caused by an aneuploidy of chr. 2 1 •92% of individuals have 3 copies of chr. 21 (47 chromosomes total) •Caused by spontaneous nondisjunction (does not run in families) •4% of individuals have a piece of chr. 21 that has translocated onto another chromosome (familial Down syndrome) •Maternal age increases are associated with higher rates of nondisjunction •Many cancerous tumor cells have extra or missing chromosomes Genetic mosaicism for the sex chromosomes produces a - ansgynandromorph Nondisjunction in a mitotic division produces - ansgenetic mosaicism Polyploidy - ans•Common in plants •Important in agriculture - used to produce larger plants and seedless fruits •Also seen in invertebrates, fishes, amphibians, reptiles •Autopolyploidy •From single species •Allopolyploidy From two species Allopolyploidy - ansFrom two species Autopolyploidy - ansFrom single species Autopolyploidy in mitosis - ans Autopolyploidy in meiosis - ans Autotriploid homologous chromosomes can pair, or not, in three ways - ans•Unequal chromosome numbers in gametes usually results in sterility. •This has been exploited in agriculture to produce seedless bananas and seedless watermelons (3n) Allopolyploids may arise from hybridization between two species followed by chromosome doubling - ans Redundancy of DNA repair mechanisms (multiple ways to repair DNA damage - ans1.Mismatch repair 2.Direct repair 3.Base-excision repair 4.Nucleotide-excision repair 5.Double stranded break repair Mismatch Repair - ans•Occurs shortly after DNA replication •Mismatched bases, small loops in DNA, and other DNA lesions •Secondary structures e.g., hairpin loops may be missed

Genetics and Heredity in BIOL 207.

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Enzymes cut out the newly synthesized strand of DNA and replace it with new nucleotides. Direct Repair - ans•Restores the correct chemical structures of altered nucleotides •E.g., UV-induced pyrimidine dimers Base-Excision repair - ans•Glycosylase enzymes recognize and remove specific types of damaged bases. •The entire nucleotide is then removed, and a section of the polynucleotide strand is replaced. Nucleotide-excision repair - ans•Removes and replaces many types of damaged DNA that distort the DNA structure. •The two strands of DNA are separated, a section of the DNA containing the distortion is removed, DNA polymerase fills in the gap, and DNA ligase seals the filled-in gap. Double-Stranded Break Repair - ans1.Homology directed repair •Same mechanism as homologous recombination we covered previously •Usually uses sister chromatid to repair break •BRCA1 and BRCA2 are enzymes involved in this process 2.Nonhomologous end joining •No 'template' used, thus is error prone •Usually occurs in G1 cell cycle stage (no sister chromatid to serve as a template) •Proteins recognize broken ends of DNA and join them together Genetic diseases and faulty DNA repair - ans•Defects in DNA repair are the underlying cause of several genetic diseases.

  • Many of these diseases are characterized by a predisposition to cancer. Xeroderma pigmentosum - ansThe disease is characterized by freckle-like spots on the skin (shown here) and a predisposition to skin cancer (1000-2000x higher risk) Types of Aneuploidy - ansnullisomy, monosomy, trisomy, tetrasomy Nullisomy - ansis the loss of both members of a homologous pair of chromosomes. It is represented as 2n − 2, where n refers to the haploid number of chromosomes. Thus, among humans, who normally possess 2n = 46 chromosomes, a nullisomic zygote has 44 chromosomes. Monosomy - ansis the loss of a single chromosome, represented as 2n − 1. A human monosomic zygote has 45 chromosomes Trisomy - ansis the gain of a single chromosome, represented as 2n + 1. A human trisomic zygote has 47 chromosomes. The gain of a chromosome means that there are three homologous copies of one chromosome. Most cases of Down syndrome, discussed later in this section, result from trisomy of chromosome 21 Tetrasomy - ansis the gain of two homologous chromosomes, represented as 2n + 2. A human tetrasomic zygote has 48 chromosomes. Tetrasomy is not the gain of any two extra chromosomes but rather the gain of two homologous chromosomes, so that there are four homologous copies of a particular chromosome. 3 factors that affect mutation rate - ans-frequency with which changes arise in DNA
  • how often these changes are repaired by DNA repair mechanisms
  • our ability to detect the mutation Radiation - ans-type of mutagen
  • high energy radiation (X-rays, gamma-rays, cosmic rays) remove electrons from atoms, altering chemical structure of bases and inducing double stranded DNA breaks. •UV radiation causes pyrimidine dimer formation (usually TT, but TC/CC also possible) •Stalls/stops DNA replication

Genetics and Heredity in BIOL 207.

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  • "Copy and Paste" Nonreplicative transposition - ans•The old copy excises from the old site and moves to a new site.
  • "Cut and Paste" RNA intermediate transposition - ans•Requires reverse transcription to integrate into the target site
  • "PDF - > copy to Word doc - > print to PDF" •Transposition in humans - ans•About 45% of the human genome comprises sequences that are related to transposable elements, mostly retrotransposons. Transposons cause mutations by - ans-Inserting into another gene
  • Promoting chromosomal rearrangements
  • Moving (deleting and inserting) genes as they move chromosomal rearrangements are generated by transposition - ans Barbara McClintock - ansdiscovered transposable elements
  • discovered activator is transposon which contains a functional transposase group gene
  • early transposition resulted in color and late results in lack of color Characteristics of two major classes of transposable elements : Class I - ans-Long terminal direct repeats; short flanking direct repeats at target site
  • Reverse-transcriptase gene (and sometimes others)
  • By RNA intermediate Characteristics of two major classes of transposable elements : Class II - ans-Short terminal inverted repeats; short flanking direct repeats at target site
  • Transposase gene (and sometimes others)
  • Through DNA (replicative or nonreplicative) Alleles - ans•Different forms of a gene that exist at a locus. Wild type allele is typically the.... - ansmost commonly found allele in a population Variant or mutant allele - ans•Different from wildtype allele •May or may not adversely affect gene product •May or may not result in detectable phenotype HOMOZYGOUS allele - ansHaving two identical alleles for a trait (EX. HH, hh)
  • If identical alleles are present on both homologous chromosomes HETEROZYGOUS allele - ansHaving two different alleles for a trait (EX. Hh, Aa)
  • If one allele is wild type* and the other allele is not (i.e., a mutant allele) The known mutant alleles for a given gene plus its wild type allele are referred to as - ansan "allelic series" or "multiple alleles" Homozygotes - ansa cell/organism with identical alleles of a gene of interest would be: FC / FC and fc / fc Heterozygotes - ansa cell/organism with one wild type copy and one mutant allele of a gene of interest would be: FC / fc Hemizygous - ansthe presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant
  • a situation where a cell/organism has only one copy of a gene/locus/chromosomal region Example of Hemizygous : Deletion - ansIn this case the corresponding gene/locus/region is deleted on the homologous chromosome Example of Hemizygous : The gene/locus/region occurs naturally in one copy - ans(true for most genes on X or Y chromosomes in a XY individual)

Genetics and Heredity in BIOL 207.

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Dominant and recessive describe the... - ansrelationship between two alleles (not two genes!) Dominant allele - ansheterozygotes individuals with one copy of the gene are phenotypically indistinguishable from the homozygotes Recessive allele - ansphenotype only observable in homozygotes heteroallelic - ansin one gene there are two different alleles resulting from different mutations

  • individual has two mutant alleles that are different from each other ex. Wild type allele: FC Mutant allele 1: fc Mutant allele 2: fc Heteroallelic cell/organism: fc1/ fc Incomplete dominance (semi-dominance) - ansheterozygotes show weaker version of phenotype than homozygotes due to only one copy of the gene being functional
  • Sometimes there is an intermediate (or blended) phenotype in the heterozygote. Codominance - anssituation in which both alleles of a gene contribute to the phenotype of the organism
  • Heterozygotes simultaneously express the phenotypes of both heterozygotes (not an intermediate phenotype) five classes of mutant alleles - ansAmorphs, Hypomorphs, Hypermorphs, Neomorphs and Antimorphs Amorphs - ansGenes that do not produce a detectable product
  • Refers to the complete loss of function of a gene Cause of Amorphs - ans•Any mutation abrogating the function of a gene, examples are:
  1. Complete deletion of the entire gene.
  2. A missense point mutation that abolishes all functions of the protein.
  3. A nonsense point mutation yielding a truncated, non-functional protein. Hypomorphs - ansa mutant gene having a similar but weaker effect than the corresponding wild type gene
  • •The allele is still partially functional, but not at the level of the wild type gene Hypermorphs - ansa mutant gene having a similar but greater effect than the corresponding wild-type gene
  • •gene is active at a level higher than the wild type gene
  • gene product did not gain a new property, there is simply either more of the normal gene product, or normal levels of a gene product with higher activity (or both).
  • the gene products are produced in cells were they would normally occur
  • ex. super buff cattle Neomorphs - ansa mutant gene having a function distinct from that of any non mutant gene of the same locus
  • •The allele is active, but has acquired a function that the wild type gene does not have •Example 1: A mutation affecting the active center of an enzyme may alter its substrate specificity. •Example 2: More commonly, a mutation in the regulatory region activates the gene in the wrong tissues or the wrong times (e.g. Burkitt Lymphoma, next slide). •Example 3: Translocations with breakpoints in genes may create new hybrid genes (see next slide, ABL) Antimorphs - ansa gene producing an effect opposite to that of the wild-type gene of the same locus