# Genetic reasoning: distinguish inheritance from the data you observe — Study worksheet

[Study guides](https://unireadinglist.com/guides/genetic-reasoning/)

[Course topic: Genetics](https://unireadinglist.com/subjects/biology/#course-genetics)

Sources checked: 2026-11-04

Study route and exercise: University Reading List editorial project.

For students with introductory biology and elementary probability. The selected works are Nickle/Barrette-Ng’s maintained online text, Introduction to Genetic Analysis twelfth-edition Digital Update and Coop’s fixed v1.2 release. The latter is an advanced extension, not a replacement for a first inheritance course. We use paper data only; no breeding procedure, genetic test or empirical experiment is proposed.

## Choose your starting point

- [ ] I need a free inheritance foundation
  Start with Online Open Genetics and work through single-gene, multiple-gene and linkage reasoning. Verify the live section title rather than inventing a publication year.

- [ ] My course needs a structured analysis text
  Use the selected twelfth-edition Digital Update when its problem sequence and coverage match the course. Check whether the assigned product requires separate Achieve access.

- [ ] I am ready for population models
  Use Coop after crosses, frequencies and probability are comfortable. Its model questions require more preparation than recognizing inheritance terminology.

## Compare the three books

### Online Open Genetics

Todd Nickle; Isabelle Barrette-Ng
Free first-course reasoning

Choose it when: You want to connect chromosomes, crosses and gene-level explanations without a purchase barrier.
Use another route when: You need an assigned proprietary exercise/platform or an advanced population-model course immediately.
Selected reading: Chapters 2–3 on meiosis/single genes,6 on multiple genes and 7 on linkage; revisit chapter 1 for DNA/gene distinctions.
Limits and trade-offs: The online text has named authors and a stated licence, but a web update is not a new print edition. Individual pages may carry additional credits.

#### Try before choosing

Use the linkage chapter to label which gametes a stipulated AB/ab parent can produce, before looking at offspring counts.
Check your work: AB and ab are parental under the supplied phase; Ab and aB are recombinant. Do not infer phase from capitalization alone.

Your notes:

________________________________

[Official free reading](https://bio.libretexts.org/Bookshelves/Genetics/Online_Open_Genetics_%28Nickle_and_Barrette-Ng%29)

[Book record and access options](https://unireadinglist.com/subjects/biology/online-open-genetics-nickle-barrette-ng/)

### Introduction to Genetic Analysis

Anthony J. F. Griffiths; John Doebley; Catherine Peichel; David A. Wassarman · 12 · 2025
Quantitative analysis spine

Choose it when: You need a connected classical-to-molecular course with systematic problem practice.
Use another route when: You only need a short free introduction or assume the print ISBN activates a platform.
Selected reading: 2025 Digital Update: 2–5 for inheritance, assortment, mapping and interaction; 18–19 only after the foundations.
Limits and trade-offs: The publisher distinguishes paperback 9781319589943 from access products and bundles. “Digital Update” describes the selected edition; it is not a general promise of online entitlement.

#### Try before choosing

From chapter 4, explain what a two-point testcross estimates and list assumptions connecting offspring counts to meiotic products.
Check your work: Name the test parent, phase, classification and survival assumptions. A count ratio is not automatically a physical DNA distance.

Your notes:

________________________________

ISBN: 9781319589943

[Book record and access options](https://unireadinglist.com/subjects/biology/introduction-genetic-analysis/)

### Population and Quantitative Genetics

Graham Coop · v1.2; third released revision
Free model-based extension

Choose it when: You can use allele/genotype frequencies, expectations and variance and want drift, selection and quantitative variation.
Use another route when: You are still unable to interpret meiosis or a two-locus cross.
Selected reading: Use v1.2’s Mendelian/population-frequency and linkage/recombination discussions, then selected drift or selection models; match headings in the released PDF.
Limits and trade-offs: The author calls it a third release, not an independently published third edition. CC BY 3.0 attribution and figure credits still matter. No current software/API instructions are inferred.

#### Try before choosing

Write down an allele-frequency model’s state, transition assumptions and observable sample; compare them with the cross in this guide.
Check your work: A population frequency and a cross-specific recombinant fraction have different units of analysis. More advanced notation does not remove an observation mechanism.

Your notes:

________________________________

[Official free reading](https://github.com/cooplab/popgen-notes/releases/tag/v1.2)

[Book record and access options](https://unireadinglist.com/subjects/biology/population-quantitative-genetics-coop/)

## Check your preparation

### Which biology must be secure?

Your notes:

________________________________

### Which probability is needed?

Your notes:

________________________________

### Is a map percentage a physical distance?

Your notes:

________________________________

## Six steps with a concrete output

- [ ] Draw the information flow

Selected reading: Online chapters 1–3; analysis-text 2.

Make this: Make a diagram linking parental genotype, meiosis, gamete, offspring genotype and observed category.

Check your work: Mark where a probability assumption or measurement rule enters.

Your notes:

________________________________

- [ ] Specify phase and a testcross

Selected reading: Online 6–7; analysis-text 3–4.

Make this: Write the four gamete categories for the supplied coupled parent and state how the test parent reveals them.

Check your work: A phenotype-only label is not silently substituted for a known genotype.

Your notes:

________________________________

- [ ] Compare expected with observed

Selected reading: The original paper case below.

Make this: Build a four-cell count table and compute the recombinant fraction; separately write independent-assortment expectations.

Check your work: Both sets total 200, but expected counts are not claimed observations.

Your notes:

________________________________

- [ ] Inspect the observation mechanism

Selected reading: Linkage discussion and the follow-up.

Make this: Draw a second stage that filters the same generated categories before counting.

Check your work: Explain which equality between generated and recorded categories has been changed.

Your notes:

________________________________

- [ ] Change the level of analysis

Selected reading: Coop’s released population-model sections.

Make this: State one population question requiring additional assumptions beyond this single cross.

Check your work: Do not infer a population’s history or a whole organism’s traits from one stipulated marker cross.

Your notes:

________________________________

- [ ] Write an auditable inference

Selected reading: Your diagrams and two solved cases.

Make this: Write a short inference with an estimated quantity, its denominator and one assumption-sensitive limit.

Check your work: A reader can reconstruct your count total and identify what new evidence would change the inference.

Your notes:

________________________________

## Worked exercise: A two-marker cross in invented plants

A stipulated plant parent has phase AB/ab and is testcrossed with ab/ab. In 200 independent recorded offspring, the revealed gamete categories are AB 96, ab 84, Ab 14, aB 6. Estimate recombinant fraction and contrast the model of independent assortment.

Assumptions: Treat markers as accurately scored and the test parent as revealing gametes without distortion. Assume equal fertilization, survival and recording probability for all categories; phase is given. These are constructed counts, not experimental results.

Your notes:

________________________________

## Change an assumption: Filtering can make the same recombination look smaller

Retain those exact 200 generated offspring and the given phase, but change observation: all parental categories survive to recording and exactly half of each recombinant category does. This deterministic paper filter yields AB 96, ab 84, Ab 7, aB 3. Compare recorded and generated fractions.

Your notes:

________________________________

## Before moving on

- I can label parental/recombinant categories from supplied phase and a test parent.
- I can distinguish generated, observed and model-expected counts in both cases.
- I can justify which textbook matches my current inference problem and name the advanced material still postponed.

## Answer and interpretation

### Which biology must be secure?

Meiosis, chromosome pairs, alleles and the difference between genotype and phenotype. Draw one meiosis before calculating a ratio.

### Which probability is needed?

Complements, conditional statements and expected counts. A prediction for many offspring is not a promise that every small family has that ratio.

### Is a map percentage a physical distance?

Not by itself. Two-point recombination can miss multiple crossover histories and depends on the specified model; do not turn it directly into base-pair distance.

### A two-marker cross in invented plants

1. Parental categories AB and ab total 180. Recombinant categories Ab and aB total 20. Thus r̂=20/200=0.10. Unequal reciprocal counts 14 and 6 do not by themselves prove a directional mechanism.
2. Under the specified independent-assortment model each category has probability 1/4, so its expected count is 50. Observed and expected tables both total 200 but differ substantially.
3. The 0.10 estimate describes this cross under the observation assumptions. Interpreting it as about 10 map units uses a short-interval approximation; it is not a measured physical DNA length or a complete crossover history.

The observed recombinant fraction is 10%, with parental phase supplied rather than guessed. The data do not resemble the stipulated equal-category expectation; no p-value, complete genome map or actual plant result is asserted.

Test the result: Check 96+84+14+6=200 and 14+6=20. State what would change if a category were misclassified or less likely to survive; the ratio alone cannot audit those mechanisms.

### Change an assumption: Filtering can make the same recombination look smaller

1. The recorded total is 190 and recorded recombinants 10, so 10/190=1/19≈5.263%. The generated recombinant fraction remains 20/200=10%.
2. Because the filter is supplied, divide recombinant counts 7 and 3 by 0.5 to reconstruct 14 and 6; parental counts remain 96 and 84. The reconstructed total is 200.

A lower recorded fraction need not mean a lower meiotic recombinant fraction. With the filter known, the original counts can be reconstructed; without survival information, the recorded table does not identify that correction.

Test the result: Both fractions use explicitly different denominators. The half-survival rule is stipulated, not an estimated property of plants; applying an inverse weight without evidence would create another unsupported assumption.

## Common mistakes

### Treating expectations as observations

A Mendelian probability specifies a model, not the exact contents of every sample.

### Skipping phase or scoring

Identify what is actually observed and why it reveals the claimed gamete.

### Overextending a marker result

A selected cross does not establish physical map length, health prediction or population history.

## Sources and edition checks

- [LibreTexts: author-attributed Online Open Genetics contents](https://bio.libretexts.org/Bookshelves/Genetics/Online_Open_Genetics_%28Nickle_and_Barrette-Ng%29)
  The author-attributed LibreTexts table of contents verifies chapters 1–7 and open access. No update timestamp is presented as a new book edition.

- [Macmillan: twelfth-edition Digital Update and formats](https://www.macmillanlearning.com/ed/uk/product/Introduction-to-Genetic-Analysis-Digital-Update--12th-edition/p/1319589944)
  Macmillan’s exact Digital Update record verifies 2025/12e, the paperback ISBN and distinct access products; its chapter map supplies the selected route.

- [Graham Coop: fixed v1.2 release and licence](https://github.com/cooplab/popgen-notes/releases/tag/v1.2)
  The author’s fixed v1.2 release supplies the book and CC BY 3.0 source/figure terms. The release label and an independent print edition are not conflated.

- [Online Open Genetics: linkage and mapping](https://bio.libretexts.org/Bookshelves/Genetics/Online_Open_Genetics_%28Nickle_and_Barrette-Ng%29/07%3A_Linkage_and_Mapping)
  The published linkage discussions supply methods context. The plant labels, counts, filter and complete solutions are original to this guide, not reported research.

These are proposed study activities, not official course assignments or a claim that every book has been read cover to cover.

[How we curate](https://unireadinglist.com/editorial/)