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Medical Science
Grade 10-12
Genetics in Medicine Cheat Sheet
A printable reference covering inheritance patterns, pedigrees, Punnett squares, genetic testing, mutations, and risk counseling for grades 10-12.
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Genetics in medicine explains how inherited traits, mutations, and chromosome changes can affect health. This cheat sheet helps students connect classroom genetics to real medical examples such as carrier screening, family history, and genetic testing. It is useful for reviewing inheritance patterns, interpreting pedigrees, and understanding how risk is estimated in families.
Key Facts
- Autosomal dominant conditions can appear in every generation, and an affected heterozygous parent has a 1 in 2 or 50% chance of passing the allele to each child.
- Autosomal recessive conditions often skip generations, and two carrier parents have a 1 in 4 or 25% chance of having an affected child.
- X-linked recessive conditions are more common in males because males have one X chromosome, so one disease-causing allele on the X can cause the condition.
- Genotype is the allele combination an individual has, while phenotype is the observable trait or medical condition that results from genes and environment.
- Punnett square probability rule: probability of a specific offspring genotype = probability of allele from parent 1 x probability of allele from parent 2.
- Carrier frequency describes how common carriers are in a population, and carrier risk helps estimate the chance of passing on a recessive condition.
- A pathogenic variant is a DNA change known to increase disease risk or cause disease, while a benign variant is not expected to affect health.
- Genetic testing results can be positive, negative, or uncertain, and results should be interpreted with family history, symptoms, and test limitations.
Vocabulary
- Allele
- An allele is one version of a gene that can contribute to a trait or medical condition.
- Pedigree
- A pedigree is a family tree diagram used to track traits, conditions, and inheritance patterns across generations.
- Carrier
- A carrier has one copy of a recessive disease-causing allele but usually does not show symptoms of the condition.
- Mutation
- A mutation is a change in DNA sequence that may be harmful, helpful, or have no noticeable effect.
- Penetrance
- Penetrance is the percentage of people with a specific genotype who actually show the related phenotype.
- Genetic Counseling
- Genetic counseling helps patients and families understand genetic risks, testing options, results, and medical decisions.
Common Mistakes to Avoid
- Assuming a skipped generation always means autosomal recessive inheritance is a mistake because dominant conditions can appear to skip generations due to reduced penetrance or missing family information.
- Treating every DNA mutation as harmful is wrong because many variants are benign and do not change health or disease risk.
- Confusing carrier with affected is incorrect because a carrier of a recessive condition usually has one normal allele and one disease-causing allele without showing the disease.
- Using one Punnett square outcome as a prediction for exactly four children is wrong because probabilities apply independently to each pregnancy, not as a guaranteed pattern.
- Ignoring sex chromosomes in pedigree problems is a mistake because X-linked inheritance produces different risk patterns in males and females.
Practice Questions
- 1 Two unaffected parents are both carriers for an autosomal recessive condition. What is the probability that their child will be affected?
- 2 A person with a heterozygous autosomal dominant condition has a child with an unaffected partner. What is the probability that the child inherits the condition?
- 3 In a pedigree, mostly males are affected, affected fathers do not pass the condition to sons, and carrier mothers can have affected sons. Which inheritance pattern is most likely?
- 4 A genetic test finds a variant of uncertain significance. Explain why doctors should not treat it the same as a confirmed pathogenic variant.