Inheritance of genetic diseases and chromosomal abnormalities
The modes of inheritance (autosomal dominant, autosomal recessive, X-linked) with risk calculation, the karyotype, and the main chromosomal abnormalities (trisomy 21, Turner and Klinefelter syndromes, translocations).
- 34 cards
- 3 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Scenarios
- Understand
A few cards from the deck
Allele: what is it?
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A version of a gene; each person carries two, one from each parent.
Homozygous: two identical alleles; heterozygous: two different ones.
Two healthy carrier parents of cystic fibrosis have a child. What is the risk the child is affected?
- One in four
- One in two
- None
- Three in four
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One in four
Each parent passes on the mutated allele half the time: ½ × ½ = ¼.
Dominant and recessive: what is it?
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Dominant: a single allele is enough to show. Recessive: two alleles are needed to show.
A healthy carrier of a recessive disease has a single mutated allele.
Why do X-linked recessive diseases mainly affect boys?
- The Y chromosome carries the disease
- Girls die before birth
- Boys have more genes
- They have only one X: a single mutated allele is enough, with no second X to compensate
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They have only one X: a single mutated allele is enough, with no second X to compensate
A girl is affected only if both her Xs carry the mutation.
Autosomal dominant inheritance: what is it?
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A single mutated allele on a non-sex chromosome is enough: each child of an affected parent has a one-in-two risk.
The disease appears in every generation; example: Huntington's disease.
A father has Huntington's disease. What is the risk for each of his children?
- One in four
- One in two
- None for daughters
- One hundred per cent
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One in two
Autosomal dominant: one mutated allele is enough, whatever the sex.