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  • Autosomal Dominant (AD):

    • Appears in every generation (vertical transmission).
    • Affected individuals usually have an affected parent.
    • Males and females affected equally.
    • Father-to-son transmission possible.
    inheritance autosomal

  • Autosomal Recessive (AR):

    • Often skips generations.
    • Affected individuals may have unaffected parents (carriers).
    • Males and females affected equally.
    • More common with consanguinity.
    inheritance autosomal

  • X-Linked Recessive:

    • More males affected than females.
    • No father-to-son transmission.
    • Affected males often have carrier mothers.
    • Daughters of affected males are carriers.
    inheritance x-linked

  • Mitochondrial Inheritance:

    • Only transmitted by mothers.
    • All children of affected mother may inherit condition.
    • Affected fathers do NOT transmit disease.
    inheritance mitochondrial

  • Imprinting:

    • Phenotype depends on parent-of-origin.
    • Maternal imprinting: maternal allele silenced.
    • Paternal imprinting: paternal allele silenced.
    • Disease may skip generations depending on transmitting parent.
    inheritance imprinting

  • Procedural Steps for Pedigree Analysis:

    • Determine if trait skips generations.
    • Check male vs female frequency.
    • Look for father-to-son transmission.
    • Check if only mothers transmit (mitochondrial).
    • Look for parent-of-origin effects (imprinting).
    pedigree procedure

  • What is the formula for recombination frequency (RF)?

    \(RF = recombinants/total \times 100\)

    linkage recombination

  • What does 1% recombination equal in mapping units?

    1% recombination = 1 map unit.

    mapping linkage

  • What RF value indicates linkage?

    RF < 50% indicates linkage.

    linkage threshold

  • Which classes are the parentals in a testcross?

    Parentals are the two largest classes in testcross.

    testcross parentals

  • What is the first step in the Testcross Playbook?

    Identify dominant phenotypes from F1.

    testcross procedure

  • What genotypes should you write in the Testcross Playbook step 2?

    Write genotypes of P and F1.

    testcross procedure

  • How are parental and recombinant classes identified in the Testcross Playbook step 3?

    Identify parental and recombinant classes.

    testcross procedure

  • Give the cis (coupling) parental example listed in the Testcross Playbook.

    Parentals can be couling/ cis (AABBxaabb= F1= AB/ab)

    testcross cis

  • Give the trans (repulsion) parental example listed in the Testcross Playbook.

    Or trans/repulsion when distorted to favor the 3 and 3 classes (AAbbxaaBB= F1= Ab/aB)

    testcross trans

  • What are steps 4 and 5 of the Testcross Playbook?

    Calculate RF. Perform chi-square if required.

    testcross procedure

  • What is the chi-square formula?

    \(\chi^2 = \sum\frac{(Observed - Expected)^2}{Expected}\)

    chi-square statistics

  • How are degrees of freedom calculated for chi-square?

    Degrees of freedom = phenotypic classes - 1.

    chi-square statistics

  • What is the null hypothesis example for linkage testing?

    The null hypothesis example for linkage: the genes are unlinked or linked and that the two traits should assort independently, giving equal numbers of each progeny class.

    chi-square null

  • State the general null hypothesis example provided.

    The null hypothesis example for...:The null hypothesis is that the genes assort independently and the observed deviation from the expected ratio occurred by chance.

    chi-square null

  • What expected ratio should be used for a Testcross?

    Testcross → 1:1:1:1

    expected ratios

  • What expected ratio should be used for a Dihybrid F1 × F1 cross?

    Dihybrid F1 × F1 → 9:3:3:1

    expected ratios

  • What expected ratio should be used for a Monohybrid cross?

    Monohybrid → 3:1

    expected ratios

  • What expected ratio applies to Hardy-Weinberg?

    HW → p²: 2pq: q²

    expected hw

  • When should you reject the null hypothesis based on P value?

    P < 0.05: reject null hypothesis (linked).

    chi-square pvalue

  • When can you not reject the null hypothesis based on P value?

    P > 0.05: cannot reject null (unlinked).

    chi-square pvalue

  • How does sample size affect statistical confidence?

    Larger sample sizes increase statistical confidence.

    statistics sampling

  • What is the first step in SECTION 4: THREE-POINT MAPPING?

    • Identify parental (largest) and double crossover (smallest) classes.
    mapping

  • What is the second step in SECTION 4: THREE-POINT MAPPING?

    • Determine middle gene by comparing parental and DCO.
    mapping

  • How do you calculate each interval distance in SECTION 4?

    • Calculate each interval distance using (SCO + DCO)/total.
    mapping recombination

  • How is Expected DCO calculated in SECTION 4?

    • Expected DCO = RF1 x RF2 x total.
    mapping recombination

  • How is Interference calculated in SECTION 4?

    • Interference = 1 - (observed DCO / expected DCO).
    mapping interference

  • What is Transition?

    • purine (G/A) to purine or pyrimidine (T,C,U) to pyrimidine.
    mutation

  • Give an example and cause of Transition from the notes.

    • G to A: transition mutation due to a possible DNA replication error, maybe chemical insult, or radiation (Xray,UV)
    mutation

  • What is Transversion?

    • purine to pyrimidine or vice versa.
    mutation

  • Give an example and cause of Transversion from the notes.

    • C to G: transversion mutation due to a possible DNA replication error, maybe chemical insult, or radiation (Xray,UV)
    mutation

  • What is Frameshift?

    • insertion/deletion not multiple of 3.
    mutation

  • What is a possible cause of Frameshift listed in the notes?

    • Could be caused by an inaltercating agent
    mutation

  • What is Nonsense?

    • premature stop codon.
    mutation

  • What is Missense?

    • amino acid substitution.
    mutation

  • What is Silent mutation?

    • no amino acid change.
    mutation

  • What does 'Nothing in coding?' note state as possibilities?

    • Must be an enhancer or 5'/3' UTR mRNA stability. DNA replication error, maybe chemical insult or radiation (Xray, UV)
    mutation

  • What does the note say about 'Insertion of several letter?'

    • splice donor error? Maybe an interacalating agent.
    mutation

  • What is the Protein Severity Ranking?

    • Silent < Conservative missense < Nonconservative missense < Late stop < Early stop < Frameshift.
    mutation severity

  • A triplet repeat expansion is:

      • An unstable increase in the 3-base repeat number
      • Caused by replication slippage
      • Often shows anticipation: Disease appears earlier and more severe in successive generations.
      • Can alter protein, transcription, or splicing
      • Detectable by larger PCR bands
    mutation triplet-repeats

  • Sex chromosome Examples:

      • XXY → Klinefelter
      • XO → Turner syndrome
      • XXX → Triple X
      • XYY → Jacobs syndrome
    chromosomes sex-chromosomes

  • Q. If DNA sequencing shows that the genes are physically closer together than the genetic map suggests, how can this be explained?

    Genetic map distance (measured in centiMorgans) reflects recombination frequency, not physical base-pair distance. Recombination does not occur uniformly across the chromosome. Some regions are recombination hotspots, where crossovers happen more frequently. This increases recombination frequency and makes genes appear farther apart on a genetic map than they are physically. Therefore, genetic distance can overestimate physical distance when recombination is elevated in that region.

    linkage recombination

  • Complementaion groups→

    cis/trans test

    complementation testing

  • Normal loss-of-function mutation in one gene, it should:

      • Fail to complement mutations in the same gene
      • Complement mutations in other genes
    mutation complementation

  • What is dominant negative?

    A dominant negative mutation produces a mutant protein that interferes with the normal protein's function

    mutation genetics

  • How To Identify Conservative vs Non-Conservative

    Look at amino acid categories: If the substitution stays in the same group → likely conservative.

    protein mutations

  • In Meselson-Stahl, what does semiconservative replication give after one generation?

    semiconservative replication gives an intermediate 'hybrid' band after one generation.

    replication molecular

  • If you never see intermediate-weight DNA, then what are the possible explanations?

    • replication is NOT semiconservative (could be conservative or dispersive-like)
    • the DNA is single-stranded (the classic density logic changes)
    replication analysis

  • What is 1 Null (Amorphic) Allele —

    Complete Loss of Function

    allele genetics

  • How do frameshift problems compare between 4 base pairs and 3 base pairs?

    So you'd expect MORE frameshift problems with 4 base pairs than us with 3 bp.

    frameshift genetics

  • Definition: (null allele)

    Produces no functional protein. Gene product activity = 0%, The gene is essentially 'dead.'

    alleles null

  • Mechanisms include: (null allele)

    • Early nonsense mutation
    • Frameshift causing premature stop
    • Severe splicing defect → nonsense-mediated decay
    • Large deletion
    • Protein completely unstable
    mechanisms null

  • Genetics pattern: (null allele)

    Usually recessive Can appear dominant if haploinsufficiency

    genetics inheritance

  • 2 Hypomorphic Allele — Partial Loss of Function (Leaky)

    2 Hypomorphic Allele — Partial Loss of Function (Leaky)

    hypomorphic alleles

  • Definition: (hypomorphic allele)

    Produces reduced amount or partially functional protein. Gene product activity = reduced but not zero. The gene works, just not well. Think: 'dim switch,' not off.

    alleles hypomorphic

  • Mechanisms include: (hypomorphic allele)

    • Missense mutation reducing activity
    • Weak promoter mutation
    • Mild splice defect
    • Protein unstable but not absent
    mechanisms hypomorphic

  • Genetics pattern: (hypomorphic allele)

    genetics hypomorphic

  • Mechanisms

    • New protein domain
    • Altered binding specificity
    • Ectopic expression (expressed in new tissue)
    • Fusion protein
    mechanisms mutation

  • Genetics pattern

    • Usually dominant
    • Wild-type allele cannot compensate
    genetics inheritance

  • Definition:

    Mutant protein interferes with normal protein function. Total activity is worse than simple heterozygous null. The mutant protein is actively harmful. Think: Normal + mutant → broken complex

    definition antimorph

  • Usually when:

    • Protein functions as a dimer/multimer
    • Mutant subunit poisons the complex
    protein structure

  • SSRs are highly polymorphic (many possible alleles per locus), whereas SNPs are usually biallelic.

    This provides greater variability and stronger discriminatory power.

    genetics markers

  • SSRs differ in length, so they can be easily detected using PCR and gel electrophoresis without sequencing, making them faster and more practical for forensic analysis.

    SSRs can be detected using PCR and gel electrophoresis without sequencing.

    forensics ssrs

  • Genes can be annotated experimentally using cDNA sequencing or computationally by identifying ORFs, regulatory signals, and conserved regions.

    Genes can be annotated experimentally using cDNA sequencing or computationally by identifying ORFs, regulatory signals, and conserved regions.

    genome annotation

  • Genome comparisons reveal synteny and chromosomal evolution, while exome comparisons reveal conserved proteins and evolutionary relationships.

    Genome comparisons reveal synteny and chromosomal evolution.

    comparative genomics

  • How do hypomorph + null explain incomplete dominance?

    Incomplete dominance happens when: phenotype is proportional to gene product dosage (enzyme amount/activity)

    inheritance dominance

  • Key's example is snapdragons: ⚘

    • Wild type allele → full enzyme activity → red
    • Null allele → zero activity → white
    • Heterozygote → half activity → intermediate pigment → pink
    example snapdragon

  • So:

    • +/+ = 100 % product → (strong phenotype)
    • +/m = 50% product → {intermediate phenotype}
    • m/m = 0 % product → {loss phenotype}
    dosage phenotype

  • Dominant

    Often more severe than haploinsufficiency

    allele severity

  • What is the table title that summarizes gene interaction and F2 genotypic ratios?

    F₂ Genotypic Ratios from an F₁ Dihybrid Cross

    genetics geneinteraction

  • What description is given for additive interaction in the table?

    Additive: Four distinct F2 phenotypes

    genetics additive

  • What F2 phenotypic ratio corresponds to additive interaction?

    9:3:3:1

    genetics additive ratios

  • How does the table define recessive epistasis?

    Recessive epistasis: When homozygous, recessive allele of one gene masks both alleles of another gene

    genetics epistasis recessive

  • What F2 phenotypic ratio is given for recessive epistasis?

    9:3:4

    genetics epistasis recessive ratios

  • How does the table define reciprocal recessive epistasis?

    Reciprocal recessive epistasis: When homozygous, recessive allele of each gene masks the dominant allele of the other gene

    genetics epistasis reciprocal

  • What F2 phenotypic ratio is given for reciprocal recessive epistasis?

    9:7

    genetics epistasis reciprocal ratios

  • How does the table define dominant epistasis I?

    Dominant epistasis I: Dominant allele of one gene hides effects of both alleles of the other gene

    genetics epistasis dominant

  • What F2 phenotypic ratio is given for dominant epistasis I?

    12:3:1

    genetics epistasis dominant ratios

  • How does the table define dominant epistasis II?

    Dominant epistasis II: Dominant allele of one gene hides effects of dominant allele of other gene

    genetics epistasis dominantii

  • What F2 phenotypic ratio is given for dominant epistasis II?

    13:3

    genetics epistasis dominantii ratios

  • How does the table define reciprocal dominant epistasis?

    Reciprocal dominant epistasis: Dominant allele of each gene masks the effects of development recessive allele of the other gene

    genetics epistasis reciprocaldominant

  • What F2 phenotypic ratio is given for reciprocal dominant epistasis?

    15:1

    genetics epistasis reciprocaldominant ratios

  • Provide the example given for recessive epistasis in the table.

    Labrador retriever: coat color (see Fig. 2.11b)

    genetics examples recessive

  • Provide the example given for reciprocal recessive epistasis in the table.

    Sweet pea: flower color (see Fig. 2.14b)

    genetics examples reciprocal

  • Where can the table image be found as a supplementary illustration?

    The image shows a table about gene interaction, F2 genotypic ratios from an F1 dihybrid cross

    genetics figure image
Notes de cours

SECTION 1: Identifying mode of inheritance

  • Autosomal dominant (AD): vertical transmission, affected parent usually present, males/females equally affected, father-to-son possible.
  • Autosomal recessive (AR): often skips generations, affected individuals can have unaffected carrier parents, equal sexes, more likely with consanguinity.
  • X-linked recessive: more males affected, no father→son transmission, affected males usually have carrier mothers, daughters of affected males are carriers.
  • Mitochondrial: transmitted only by mothers; all children of an affected mother can inherit the trait; affected fathers do not transmit.
  • Imprinting (parent-of-origin effects): one allele is epigenetically silenced depending on parent; phenotype depends on which parent transmitted the allele.

Procedural checklist for pedigree analysis: 1. Look for generation skipping (suggests recessive or imprinting patterns). 2. Compare male vs female incidence. 3. Search for father→son transmission (indicates autosomal). 4. Check if only mothers transmit (mitochondrial). 5. Consider parent-of-origin effects (imprinting).

SECTION 2: Linkage & recombination

  • Recombination frequency (RF): measure of genetic distance:
  • \[\text{RF} = \frac{\text{number of recombinants}}{\text{total progeny}} \times 100\%\]
  • 1% recombination = 1 map unit (cM).
  • RF < 50% indicates linkage; RF = 50% implies independent assortment.
  • Map vs physical distance: genetic (cM) distance reflects crossover frequency, not base pairs; hotspots can make genes appear farther apart than physical distance.

Testcross playbook (practical steps): 1. Identify dominant phenotypes in F1 and set up genotypes of parents and F1. 2. Determine parental (largest) and recombinant (smaller) classes. 3. Distinguish cis (coupling) vs trans (repulsion) phase in the F1. 4. Compute RF and, if needed, perform chi-square to test expected ratios.

SECTION 3: Chi-square analysis (goodness-of-fit)

  • Formula:
  • \[\chi^2 = \sum \frac{(O - E)^2}{E}\]
  • Degrees of freedom: \(\(\text{df} = \text{number of phenotypic classes} - 1.\)\)
  • Common null hypotheses & expected ratios:
  • Testcross: \(1:1:1:1\)
  • Dihybrid F1\times F1: \(9:3:3:1\)
  • Monohybrid: \(3:1\)
  • Hardy–Weinberg: \(p^2:2pq:q^2\)
  • Decision rule: if \(P<0.05\) reject the null (significant deviation, e.g., linkage); if \(P>0.05\) cannot reject (consistent with expectation).
  • Larger sample sizes give more reliable chi-square tests.

SECTION 4: Three-point mapping

Stepwise procedure: 1. Identify parental classes (largest counts) and the double-crossover (DCO) class (smallest counts). 2. Compare a parental genotype to the DCO to identify the middle gene. 3. Calculate interval distances (in map units): for each interval - \(\(\text{distance} = \frac{\text{single crossovers} + \text{double crossovers}}{\text{total}} \times 100\%.\)\) 4. Expected DCO count (when using recombination fractions): - \(\(\text{expected DCO} = \text{RF}_{12} \times \text{RF}_{23} \times \text{total}\)\) (use RF as a fraction, not percent, when multiplying). 5. Interference measures how much fewer DCOs occur than expected: - \(\(\text{Interference} = 1 - \frac{\text{observed DCO}}{\text{expected DCO}}.\)\)

SECTION 5: Mutation types & consequences

  • Transition: purine↔purine (A↔G) or pyrimidine↔pyrimidine (C↔T); common from replication errors or chemical damage.
  • Transversion: purine↔pyrimidine (e.g., C↔G); less frequent than transitions.
  • Frameshift: insertion/deletion not multiple of 3 bases; usually alters downstream amino-acid sequence and often creates premature stops.
  • Nonsense: substitution creates a premature stop codon → truncated protein.
  • Missense: amino-acid substitution; severity depends on conservative vs nonconservative change.
  • Silent (synonymous): codon changes but amino acid unchanged; may still affect splicing or mRNA stability.
  • Regulatory / noncoding changes: mutations in enhancers, promoters, or UTRs can affect expression or mRNA stability without altering coding sequence.
  • Triplet repeat expansion: replication slippage increases repeat number, often shows anticipation (earlier/more severe in successive generations); detectable as larger PCR products.

Protein-severity ranking (general): - Silent < Conservative missense < Nonconservative missense < Late stop < Early stop < Frameshift

SECTION 6: Allele classes and genetic behavior

  • Amorphic (null): no functional product (0% activity). Mechanisms: early nonsense, frameshift, large deletion, NMD; usually recessive, but haploinsufficiency can make it appear dominant.
  • Hypomorphic (leaky): reduced activity; mechanisms: weak promoter, partial splice defect, destabilizing missense; often recessive or show dosage/partial dominance.
  • Hypermorphic: increased normal function (more protein or activity), e.g., promoter upregulation or gene duplication; often dominant and dose-dependent.
  • Neomorphic: new function or ectopic expression; usually dominant because WT allele cannot compensate.
  • Dominant negative (antimorph): mutant protein interferes with WT (common for multimeric proteins); phenotype often more severe than simple loss and is dominant.

How dosage explains incomplete dominance (example): - If phenotype scales with enzyme activity: \(+/+\) = 100% (wild type), \(+/m\) = 50% (intermediate), \(m/m\) = 0% (mutant), giving intermediate heterozygote phenotype (e.g., snapdragon red/pink/white).

SECTION 7: Complementation & mapping considerations

  • Complementation test: mutations in the same gene fail to complement (mutant phenotype in trans-heterozygote); mutations in different genes complement.
  • SSR vs SNP: SSRs (microsatellites) are multi-allelic and length-variable, ideal for high polymorphism and PCR-based detection; SNPs are usually biallelic and used for high-density genotyping.
  • Gene annotation: experimental (cDNA/sequencing) and computational (ORF prediction, conserved motifs); comparative genomics reveals synteny and evolutionary relationships.

SECTION 8: Gene interaction & F2 ratios (practical summary)

  • Dihybrid F2 phenotypic/genotypic ratios change when genes interact (epistasis). Common patterns and their F2 phenotypic ratios:
  • Additive (no interaction): \(9:3:3:1\)
  • Recessive epistasis: \(9:3:4\)
  • Reciprocal recessive epistasis: \(9:7\)
  • Dominant epistasis I: \(12:3:1\)
  • Dominant epistasis II: \(13:3\)

  • Reciprocal dominant epistasis: \(15:1\)

  • See the included table for a compact summary of F2 genotypic ratios and examples.

F2 genotypic ratios table

Alt text: F2 genotypic ratios table summarizing epistasis examples.

SECTION 9: Quick facts & exam-ready tips

  • Always state the null hypothesis clearly for chi-square tests (e.g., independent assortment).
  • Use parental vs recombinant class sizes to infer linkage and phase (cis/trans).
  • For three-point mapping, determine the middle gene by comparing parental and DCO genotypes.
  • When interpreting mutation effects, consider molecular mechanism (coding vs regulatory) and biochemical context (multimeric proteins → dominant negative risk).
  • Remember Meselson–Stahl: semiconservative replication gives a single intermediate-density band after one generation; absence of an intermediate suggests different replication pattern or single-stranded DNA.

Quick-reference formulas

  • \[\text{RF (\%)} = \frac{\text{recombinants}}{\text{total}} \times 100\]
  • \[\chi^2 = \sum \frac{(O - E)^2}{E}\]
  • \[\text{expected DCO} = \text{RF}_{12} \times \text{RF}_{23} \times \text{total}\]
  • \[\text{Interference} = 1 - \frac{\text{observed DCO}}{\text{expected DCO}}\]