Exam 3 Flashcards
Chloroplast DNA (cpDNA) Heredity
maternally inherited
Green (Normal cpDNA) – In healthy plants, chloroplasts contain functional genes for chlorophyll production, resulting in green leaves due to efficient photosynthesis.
White or Yellow (Mutant cpDNA) – Some mutations disrupt chlorophyll biosynthesis, leading to chloroplasts that lack pigmentation, causing white or yellow sectors in leaves.
Variegation (Mixed cpDNA Populations - Heteroplasmy) – Some plants inherit a mix of normal and mutant chloroplasts, leading to patchy green and white/yellow patterns on leaves. This can occur due to random segregation of cpDNA during cell division.
Mitochondrial DNA (mtDNA)
inherited maternally
double-stranded circular D N A
A cell can contain a mix of normal and mutated mtDNA
Threshold Effect – Symptoms of mtDNA mutations appear when the percentage of mutated mitochondria crosses a certain threshold
Endosymbiotic theory (Lynn Margulis et al.)
Mitochondria and chloroplasts (organelles) arose independently 2 billion years ago from free-living bacteria
Organelles possessed attributes of aerobic respiration and photosynthesis, respectively
m t D N A susceptible to mutations
No structural protection from histones
D N A repair mechanism limited
High concentrations of R O S (reactive oxygen species) generated by cell respiration
The Particle Theory of Inheritance
states that hereditary traits act like particles, units, or factors as they are passed from generation to generation.
Law of Segregation
states that his hereditary factors do not blend but remain distinct during breeding—thus, disproving the blending theory.
Law of Independent Assortment
which states that character traits are not connected but are inherited independent of one another
Map distance math
(recombinant #)/total X 100
Chi square math
(Expected-observed)^2/observed
Add together
Degree of freedom: # of freedom - 1
Three-point
Cross two true-breeding strains that differ with regard to three alleles
Perform a testcross by mating F1 female heterozygotes to male flies that are homozygous recessive for all three alleles
Collect and analyze data from F2 offspring (propose a hypothesis, apply the chi square formula and interpret the chi square value)
Calculate the map distance between pairs of genes
Construct the map
Aneuploidy
involves a condition where one or a few chromosomes are added or deleted from the normal chromosome number
Euploidy
a state where the chromosome number is an exact multiple of the basic chromosome set,
Nondisjunction
Paired homologs fail to separate during segregation
monosomy
a chromosomal abnormality that occurs when a cell has only one chromosome from a pair, instead of the usual two
trisomy
a genetic condition where an individual has an extra copy of a specific chromosome
Chromosomal Deletion
a genetic mutation where a portion of a chromosome is missing
Duplications
usually caused by abnormal events during recombination
Repetitive sequences can cause misalignment between homologous chromosomes.
If a crossover occurs, nonallelic homologous recombination results
Chromosomal Inversion
A chromosome with an inversion has a segment that has been flipped to the opposite orientation
Paracentric inversion heterozygote results in gametes
One gamete with normal chromosome
One gamete dicentric (two centromeres; duplication and deletion)
One gamete with inversion
One gamete acentric (no centromere; duplication and deletion)
Chromosomal Paracentric inversion
a chromosomal rearrangement that occurs when a chromosome breaks in two places on the same arm. The broken segment is then reinserted after a 180° rotation.
Pericentric inversion heterozygote results
One gamete with normal chromosome
One gamete with inversion
Two gametes with duplications and deletions
Chromosomal Pericentric inversion
a chromosomal rearrangement where a segment of a chromosome, including the centromere, is inverted, meaning it’s flipped 180 degrees and reinserted into the chromosome.
Translocations
a chromosomal abnormality that occurs when parts of two chromosomes are exchanged or fused
Mutation
a heritable change in the genetic material
Mutations provide allelic variations
- Chromosome mutations
Changes in chromosome structure
Deletions, insertions, duplications, translocations
- Genome mutations
Changes in chromosome number
Euploidy (multiple of all), aneuploidy (multiple of one)
- Gene mutations
Relatively small change in DNA structure that affects a single gene
transition base
a change of a pyrimidine (C, T) to another pyrimidine or a purine (A, G) to another purine
transversion base
a change of a pyrimidine to a purine or vice versa
Spontaneous mutation:
Changes in nucleotide sequence that occur naturally
Arise from normal biological or chemical processes that alter nitrogenous bases
Spontaneous mutation rates vary, but are exceedingly low for all organisms
Spontaneous Tautomeric Shifts
Enols may form due to tautomeric shifts in which a carbonyl group will be converted into a hydroxy group or an amine group may convert into an imino group.
Changes available donor and acceptors with nitrogenous bases
Induced Mutations
changes in the number or structure of chromosomes caused by environmental factors or mutagens like chemicals or radiation
Alkylating agent mutagens
Adding alkyl groups (methyl, ethyl, propyl, etc) to an amino or keto group
Alter base-pairing affinity
Intercalating Agents
Chemicals with dimensions and shapes that wedge between D N A base pairs
This causes base-pair distortions and D N A unwinding
Forces bulges in DNA so it cannot be unbound
Base analogs (mutagenic chemicals)
Can substitute for purines or pyrimidines during nucleic acid biosynthesis
Increase tautomeric shifts
Increase sensitivity to U V light—mutagenic
Example: 5-Bromouracil behaves as thymine analog
U V Light—Pyrimidine Dimers
Two identical pyrimidines that distort D N A conformation
Errors can be introduced during D N A replication
Nucleotide Excision Repair
This type of system can repair many types of DNA damage, including
Thymine dimers and chemically modified bases missing bases, some types of crosslinks
Two types of excision repair
Base excision repair (B E R)
Nucleotide excision repair (N E R)
Base excision repair (B E R)
Corrects D N A containing a damaged D N A base
D N A glycosylase recognizes altered base
Nucleotide excision repair (N E R)
Repairs bulky lesions that alter/distort double helix
Base and nucleotide excision repair steps
Recognition of mutation (eg: deamination of cytosine to uracil which uracil DNA glycosylase can immediately detect uracil in DNA)
Excision of mutated base (the strand is broken with AP endonuclease between polypeptide bonds)
Repair (the other strand is used as a template to fill in the gap with Pol and ligase)
D N A Repair associated with DNA replication
Proofreading and mismatch repair
D N A polymerase “proofreads,” removes and replaces incorrectly inserted nucleotides
Mismatch repair (if proofreading fails) becomes activated
Mismatches are detected, cut, and removed (endonuclease and exonuclease).
Correct nucleotide inserted by D N A polymerase
Strand Discrimination
Based on D N A methylation
Adenine methylase (enzyme in bacteria) recognizes D N A sequences and adds methyl group to adenine residues
Newly synthesized strand of replication remains unmethylated
Mismatch repair recognizes unmethylated strand and repairs
Postreplication Repair
Responds after damaged D N A has escaped repair and has failed complete replication
RecA protein directs recombination exchange with corresponding region on undamaged parental strand (donor D N A)
Gap can be filled in by repair synthesis
Double-Strand Break Repair - 2
Homologous recombination repair pathway
Nonhomologous end joining pathway
Homologous recombination repair pathway
Recognizes break, digests 5’ end, and leaves 3’ overhang
3’ end aligns with sequence complementary on sister chromatid
Occurs during late S or early G2 phase of cell cycle
Nonhomologous end joining pathway
Activated in G1 prior to replication
Repairs double-strand breaks
Complex of proteins is involved in end joining
May include kinase and B R C A 1
Proteins bind free ends and ligate ends back together
