## Questions and Answers

In an autosomal dominant disorder, if one parent is affected by the disorder and the other parent is a carrier, what is the probability that their child will be phenotypically normal?

75%

If both parents are carriers of an autosomal recessive disorder, what is the probability that their child will inherit the disorder?

25%

For an autosomal dominant disorder, if both parents are carriers of the disorder, what is the probability that their child will also be a carrier?

100%

If a parent is homozygous dominant for an autosomal dominant disorder and the other parent is heterozygous, what is the probability that their child will inherit the disorder?

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In a Punnett square for an autosomal recessive disorder where both parents are carriers, what is the probability that they will have a child who is not a carrier?

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For an autosomal dominant disorder, if one parent is asymptomatic and the other parent is affected by the disorder, what is the probability that their child will be a carrier?

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Which genetic disorder is associated with a positive triple screen test on maternal blood followed by amniocentesis?

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What is the karyotype of an individual with Down syndrome?

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Which of the following is NOT an abnormality associated with Down syndrome?

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What is a characteristic appearance of an individual with Down syndrome?

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What developmental delay is commonly seen in individuals with Down syndrome?

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In Punnett Square A, which parent is genotypically and phenotypically normal?

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In Punnett Square B, which parent is a carrier of the disorder?

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What is the probability that a couple, like in Punnett Square A, will produce a son with the disorder?

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In the context of genetic disorders, what does the term 'carrier' refer to?

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What is the probability that a couple, like in Punnett Square B, will produce a daughter who is a carrier of the disorder?

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Which statement accurately represents an autosomal dominant disorder?

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## Study Notes

### Autosomal Dominant Disorders

- If one parent is affected and the other is a carrier, the probability of their child being phenotypically normal is 50%.
- If both parents are carriers, the probability of their child being a carrier is 50%, and the probability of inheriting the disorder is 25%.
- If one parent is homozygous dominant and the other is heterozygous, the probability of their child inheriting the disorder is 100%.

### Autosomal Recessive Disorders

- If both parents are carriers, the probability of their child inheriting the disorder is 25%, and the probability of not being a carrier is 2/3 or approximately 67%.
- In a Punnett square for an autosomal recessive disorder, the probability of having a child who is not a carrier is 2/3 or approximately 67%.

### Genetic Disorders

- A positive triple screen test on maternal blood followed by amniocentesis is associated with Down syndrome.
- The karyotype of an individual with Down syndrome is 47, XY or 47, XX.
- Down syndrome is not associated with polydactyly.
- Characteristic appearances of individuals with Down syndrome include almond-shaped eyes, a flat face, and a small nose.
- Developmental delays are commonly seen in individuals with Down syndrome.

### Punnett Squares

- In Punnett Square A, the parent that is genotypically and phenotypically normal is the mother (bb).
- In Punnett Square B, the parent that is a carrier of the disorder is the father (Bb).
- The probability that a couple, like in Punnett Square A, will produce a son with the disorder is 25%.
- The probability that a couple, like in Punnett Square B, will produce a daughter who is a carrier of the disorder is 50%.

### Genetics Terminology

- A carrier is an individual who is heterozygous for a particular genetic disorder, meaning they have one normal and one mutated allele.
- An autosomal dominant disorder is characterized by a single mutated allele being enough to express the disorder, and each affected individual has a 50% chance of passing the mutated allele to each offspring.

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