25 April 2017
• X-Rays are the major source of exposure to human-made radiation.
• Effects of a mutation:
o Loss-of-function: Gene’s product is reduced or absent
o Gain-of-function: Gene’s activity changes
• Steps that occur during excision repair in E. coli in a sequential order:
o Enzymes cut the bond between the DNA sugar and base.
o The pyrimidine dimer and surrounding bases are exercised.
o A DNA polymerase fills in the correct nucleotides, using the exposed template as a
o DNA polymerase also detects and corrects mismatched bases in newly replicated DNA.
• Mutations that lead to allelic disorders:
o Altering the protein in ways that affect its interactions with other proteins.
o A missing gene.
o A single base change.
• A natural consequence of DNA’s ability to change that affects the phenotype only under certain
circumstances in known as conditional mutation.
• An expanding repeated disease is a myotonic dystrophy.
• Steps that occur in mutational hot spots in a sequential order:
o DNA strands locally unwind to replicate in symmetrical or repeated sequences.
o Bases located on the same strand may pair.
o A loop is created that interferes with replication and repair enzymes.
o Errors may result.
• Accidental exposures to mutagens that can occur:
o Industrial accidents
o Natural disasters that damage radiation-emitting equipment.
o Medical treatments such as chemotherapy and radiation.
• Mutagens are chemicals or radiation that delete, substitute, or add bases and hence cause
• A skipped exon causes familial dysautonomia.
• Steps that occur during the formation of collagen in a sequential order:
o The three procollagen chains coil into a very regular triple helix, with glycine in the
o Enzymes snip off the ragged ends of the polypeptides, forming mature collagen.
o The collagen fibrils continue to associate with each other outside the cell, building
networks that hold it together.
• Unlike a mutation, a polymorphism does not harm health.
• Allelic disorders: o Spondyleopimetaphyseal dysplasia with joint laxity, type 1 (SEMD-JL1) Prominent
with blue sclerae, long upper lips, small jaws with cleft palate, poor muscle tone,
bowling of the back and limbs, and splayed fingers with short nails.
o Ehlers-Danlos syndrome progeroid type Hyperextensible joints and loose elastic skin
that scars easily.
• Gonadal mosaicism occurs if only some sperm or oocytes have a mutation because of a
spontaneous mutation that occurred in the developing testis or ovary.
• A minisatellite size in a child that does not match the size of either parent indicates that a
mutation occurred in a parent’s gamete.
• Some organs that gets destroyed as severe beta thalassemia progresses are:
o Endocrine glands
• Modes of mutagens:
o Alkylating agents Remove a DNA base, which is replaced with any of the four bases.
o Dyes Add or remove a single DNA base
o X rays and other forms of radiation Delete a few bases or break chromosomes
• The DNA sequences that differ in number from person to person are called copy number
• Steps that lead to development of the disorder alpha thalassemia in a sequential order:
o Four genes that specify alpha goblin chains, two next to each other are found on each
o Homologs with repeated genes can misalign during meiosis when the first sequence on
one chromosome lies opposite the second sequence on the homolog.
o Crossing over result in a sperm or oocyte that has one or three alpha goblin genes
instead of the normal two.
o Fertilization with a normal gamete results in a zygote with one extra or one missing
alpha goblin gene.
• Different disease phenotypes caused by mutations in the same gene are termed allelic
• A point mutation that changes a codon that normally specifies a particular amino acid into one
that codes for a different amino acid is called a(n) missense mutation.
• Stages of sickle cell disease in the order in which progresses in an individual:
o Valine changes the surfaces of hemogoblin molecules so that in low-oxygen conditions
they attach at many more points.
o The aggregated hemogoblin molecules form ropelike cables that at first make red blood
cells sticky and able to deform.
o The red blood cells bend into rigid, fragile, sickle-shaped structures.
o The misshapen cells lodge in narrow blood vessels, cutting off local blood supplies.
o Sickling speeds up and spreads, as the oxygen level falls.
o Great pain is felt in the blocked body parts, particularly the hands, feet, and intestines.
• Nucleotide excision repair, a DNA repair mechanism in humans replaces up to 30 nucleotides
and removes errors that result from several types of insults, including exposure to chemical
carcinogens, UVB in sunlight, and oxidative damage. • A limitation of using a mutagen is that it cannot cause a specific mutation.
• A mutation changes the DNA sequence from CAC CTG ACT CCT to CAC CTG TCT CCT. Identify the
type of mutation that has occurred is called a transversion.
• Two copies of a gene next to each other is a type of mutation called a tandem duplication.
• Steps in the mechanism of triplet repeat disorders in a sequential order:
o The bases of repeated triplets bond to each other in way