Inheritance, variation and probability
הוצג| English | משמעות |
|---|---|
| allele/əˈliːl/ | אלל |
| genotype/ˈdʒenətaɪp/ | גנוטיפ |
What would explain this observation?
- Two parents can carry a recessive allele 等位基因 without expressing the associated phenotype. Their children do not have to match the parents phenotypically.
Build the model
- An allele is a variant of a gene.
- A genotype 基因型 lists alleles; a phenotype is the expressed characteristic, influenced by genotype and sometimes environment.
- Dominant and recessive describe the relationship between alleles, not how common they are.
- allele: A variant of a gene.
- genotype: The alleles an organism carries.
What does a 25% probability in Aa × Aa mean?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
The 25% is a probability for each fertilization under the model: each child of Aa x Aa parents has a one-quarter chance of aa. Chance has no memory, so no fixed number of aa children is guaranteed in any family of four.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- In a simple monohybrid cross Aa × Aa, gametes carry A or a.
- Combining independent gametes gives AA, Aa, Aa and aa.
- The predicted probabilities describe many possible fertilizations, not a fixed order of children.
In the lab: Write parental genotypes and gametes before making the grid. State the inheritance model and phenotype key. Use a pedigree to check consistency with a model; do not infer certainty from a small family alone.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: Aa × Aa with complete dominance.
- Probability of aa = 1/4 = 25%.
- Probability of the dominant phenotype = 3/4 = 75%.
- If four children are born, there is no guarantee that exactly one has the recessive phenotype.
Your turn: In Aa × aa, what percentage of offspring are predicted to be aa?
In Aa × aa, what percentage of offspring are predicted to be aa?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 50 %. Known: cross Aa x aa. Gametes are A and a from one parent, a and a from the other. Offspring: Aa, Aa, aa, aa. Predicted aa proportion = 2/4 = 50%. This is a model prediction; small real families can deviate from it.
Check the conclusion and its limits
- A dominant allele can be rare.
- Mutation is a source of new variation; selection changes the relative success of existing variants rather than directing mutations toward a goal.
Not true: A dominant allele must be the most common allele in a population. Dominant describes how an allele is expressed in a heterozygote, not how common it is. A dominant allele can be rare in a population and a recessive allele can be common; frequency depends on inheritance and selection, not dominance.
- An allele is a variant of a gene.
- In a simple monohybrid cross Aa × Aa, gametes carry A or a.
- Watch for: A dominant allele can be rare.
A dominant allele must be the most common allele in a population.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Dominant describes how an allele is expressed in a heterozygote, not how common it is. A dominant allele can be rare in a population and a recessive allele can be common; frequency depends on inheritance and selection, not dominance.
A variant of a gene: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
allele means A variant of a gene.