Inherited disorders and screening judgements
| English | 中文 | Pinyin |
|---|---|---|
| carrier/ˈkærɪə/ | 携带者 | xié dài zhě |
| embryo screening/ˈembrɪəʊ ˈskriːnɪŋ/ | 胚胎筛查 | pēi tāi shāi chá |
What would explain this observation?
- A person can carry a recessive allele without expressing the disorder in a simple model. Screening results and ethical decisions answer different questions.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- The specification uses polydactyly, extra fingers or toes, as an example of a dominant inherited allele. It uses cystic fibrosis, a disorder of cell membranes, as a recessive example. In a supplied simple model with F as the non-disorder allele and f as recessive, FF and Ff do not express the disorder while ff does. Ff is a carrier 携带者.
- carrier: An individual carrying a recessive allele without expressing the disorder in the stated model; embryo screening 胚胎筛查: Testing embryos for specified genetic information before a decision about selection.
In the supplied Ff×Ff model, which genotype is a carrier?
For a supplied Ff×Ff grid, the expected outcomes are FF, Ff, Ff and ff. Each offspring has a 1/4 chance of ff, a 1/2 chance of being a carrier and a 3/4 chance of not expressing the disorder in this model. Not expressing the disorder is not the same as not carrying its allele. Use the prompt’s explicit allele key; letter choice alone does not define dominance.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- For a supplied Ff×Ff grid, the expected outcomes are FF, Ff, Ff and ff. Each offspring has a 1/4 chance of ff, a 1/2 chance of being a carrier and a 3/4 chance of not expressing the disorder in this model. Not expressing the disorder is not the same as not carrying its allele. Use the prompt’s explicit allele key; letter choice alone does not define dominance.
- Interpret provided grids and family trees, then consider embryo screening using the evidence supplied. Discuss possible reduction of suffering, cost, access, embryo selection and differing ethical views. Separate what screening can detect from the decision people make with that information. No student should be asked to disclose genetic diagnoses or make personal treatment decisions in class.
Which two habits make the investigation or model in this case more defensible?
Interpret provided grids and family trees, then consider embryo screening using the evidence supplied. Discuss possible reduction of suffering, cost, access, embryo selection and differing ethical views. Separate what screening can detect from the decision people make with that information. No student should be asked to disclose genetic diagnoses or make personal treatment decisions in class.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: the given model predicts 1/4 affected offspring. Among 160 independent model offspring, expected number = 160×1/4 = 40. Carrier expectation is 160×1/2 = 80. These are expectations, not a forecast for one family or a measure of screening accuracy.
A provided Ff×Ff model predicts affected probability 1/4. Find expected affected count in 360 offspring. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A provided Ff×Ff model predicts affected probability 1/4. Find expected affected count in 360 offspring.
The result is 90 offspring. Known: the given model predicts 1/4 affected offspring. Among 160 independent model offspring, expected number = 160×1/4 = 40. Carrier expectation is 160×1/2 = 80. These are expectations, not a forecast for one family or a measure of screening accuracy.
Check the conclusion and its limits
- Dominant inheritance does not mean every child of an affected parent must be affected. A heterozygous dominant parent and a homozygous recessive parent can produce both phenotypes. Real clinical interpretation may be more complex; classroom conclusions are restricted to the supplied model.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Not expressing a recessive disorder proves an individual carries no recessive allele. This claim is false: Dominant inheritance does not mean every child of an affected parent must be affected. A heterozygous dominant parent and a homozygous recessive parent can produce both phenotypes. Real clinical interpretation may be more complex; classroom conclusions are restricted to the supplied model.
Inherited disorders and screening judgements: For a supplied Ff×Ff grid, the expected outcomes are FF, Ff, Ff and ff. Each offspring has a 1/4 chance of ff, a 1/2 chance of being a carrier and a 3/4 chance of not expressing the disorder in this model. Not expressing the disorder is not the same as not carrying its allele. Use the prompt’s explicit allele key; letter choice alone does not define dominance.
Not expressing a recessive disorder proves an individual carries no recessive allele.
Dominant inheritance does not mean every child of an affected parent must be affected. A heterozygous dominant parent and a homozygous recessive parent can produce both phenotypes. Real clinical interpretation may be more complex; classroom conclusions are restricted to the supplied model.
An individual carrying a recessive allele without expressing the disorder in the stated model: write the technical term.
carrier means An individual carrying a recessive allele without expressing the disorder in the stated model.