AGRI10051 Chap.6 Independent Assortment, Dihybrid Ratios and Multi-Locus Probability
Independent Assortment, Dihybrid Ratios and Multi-Locus Probability
Make multi-locus crosses manageable by decomposing them into one-locus events and combining probabilities only when independence is justified. The chapter explains dihybrid ratios, gamete enumeration, product and sum rules, and conditional questions without relying on oversized Punnett squares. You will learn exactly when linkage breaks the shortcut.
What this chapter covers
- 01
Scale by decomposition, not by a larger square: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 02
Decompose the cross: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 03
One allele per locus in every gamete: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 04
Homozygous loci do not double the list: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 05
Probabilities can be unequal: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 06
Use the complement: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 07
A product of two 3:1 phenotype partitions: use the chapter explanation to connect mechanism, model, evidence and limitation.
- 08
Ratio assumptions: use the chapter explanation to connect mechanism, model, evidence and limitation.
Scale by decomposition, not by a larger square
- +1EX 6.1 Find one four-locus genotype Question. Under independent assortment, what proportion of offspring from AaBbCcDd × aaBbCCDd are aaBbCcdd? At A: Aa × aa gives P(aa) = 1/2.
- +2At B: Bb × Bb gives P(Bb) = 1/2. At C: Cc × CC gives P(Cc) = 1/2. At D: Dd × Dd gives P(dd) = 1/4.
- +3Because the four locus outcomes are assumed independent, multiply: (1/2)(1/2)(1/2)(1/4) = 1/32 = 0.03125 = 3.125% . The check is that every requested genotype is possible from its local parents. A single impossible local event would make the overall probability zero, regardless of the other loci.
- +4State the genetic model and assumptions, show the working in labelled stages, and finish with a qualified biological interpretation.
Key terms
- independent assortment
- The model in which allele transmission at one locus does not change the gamete probabilities at another locus.
- Model solution
- A key chapter term that must be defined in relation to the stated genetic model and evidence.
- Expected outcome
- In Independent Assortment, Dihybrid Ratios and Multi-Locus Probability, this is made explicit so a reader can trace the conclusion back through the chapter’s mechanism, working and evidence.
- Observed evidence
- In Independent Assortment, Dihybrid Ratios and Multi-Locus Probability, this is made explicit so a reader can trace the conclusion back through the chapter’s mechanism, working and evidence.
- Biological interpretation
- In Independent Assortment, Dihybrid Ratios and Multi-Locus Probability, this is made explicit so a reader can trace the conclusion back through the chapter’s mechanism, working and evidence.
- Limitation
- In Independent Assortment, Dihybrid Ratios and Multi-Locus Probability, this is made explicit so a reader can trace the conclusion back through the chapter’s mechanism, working and evidence.
- Validation
- In Independent Assortment, Dihybrid Ratios and Multi-Locus Probability, this is made explicit so a reader can trace the conclusion back through the chapter’s mechanism, working and evidence.
Independent Assortment, Dihybrid Ratios and Multi-Locus Probability FAQ
What is the central reasoning task in Independent Assortment, Dihybrid Ratios and Multi-Locus Probability?
Make multi-locus crosses manageable by decomposing them into one-locus events and combining probabilities only when independence is justified. The chapter explains dihybrid ratios, gamete enumeration, product and sum rules, and conditional questions without relying on oversized Punnett squares. You will learn exactly when linkage breaks the shortcut.
Which mistake should I actively check for?
Do not multiply one-locus probabilities until independence has been justified. Linked loci require phase-specific gamete probabilities, so the product shortcut can produce a tidy but wrong answer.
How much working should a genetics answer show?
EX 6.1 Find one four-locus genotype Question. Under independent assortment, what proportion of offspring from AaBbCcDd × aaBbCCDd are aaBbCcdd? At A: Aa × aa gives P(aa) = 1/2. At B: Bb × Bb gives P(Bb) = 1/2. At C: Cc × CC gives P(Cc) = 1/2. At D: Dd × Dd gives P(dd) = 1/4. Because the four locus outcomes are assumed independent, multiply: (1/2)(1/2)(1/2)(1/4) = 1/32 = 0.03125 = 3.125% .
The check is that every requested genotype is possible from its local parents. A single impossible local event would make the overall probability zero, regardless of the other loci.
How should I revise this chapter?
Rebuild one diagram or cross without notes, solve the worked example with changed labels and numbers, then explain the conclusion aloud. Record the first incorrect line as a model, representation, operation or interpretation error. Return two days later and repeat a fresh problem so delayed reconstruction, rather than immediate recognition, is doing the work.
Exam move
Study Independent Assortment, Dihybrid Ratios and Multi-Locus Probability as a decision sequence. Start with these navigation points: Scale by decomposition, not by a larger square; Decompose the cross; One allele per locus in every gamete; Homozygous loci do not double the list; Probabilities can be unequal. For each, write the biological mechanism, the model assumptions, a predicted observation and one limitation.
Cover the chapter answer and reconstruct its symbols and arithmetic. Change one premise—phase, dominance, sample size, environment or population—and predict which lines must change before recalculating. Use the glossary for active recall, not copying: define each term, contrast it with its nearest neighbour and give one observation that discriminates them.
Finish with a timed explanation that shows setup, working and a qualified conclusion. Revisit the first error after a delay and solve a new version rather than memorising the displayed numbers.
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