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terms list
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individual through whom the family came to your attention (arrow)
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individual seeking you advice (C double bar)
Autosomal dominant:
Vertical pedigree pattern, with multiple generations affected, Each affected person normally has one affected parent, Each child of an affected person has a 1 in 2 chances of being affected, Males and females are equally affected and equally likely to pass the condition on
Autosomal recessive:
A horizontal pedigree pattern, with one or more sibs affected; often only a single affected case, Parents and children of affected people are normally unaffected, Each subsequent sib of an affected child has a 1 in 4 chance of being affected, Males and females are equally affected, Affected children are sometimes the product of consanguineous marriages. In families with multiple consanguineous marriages, affected individuals may be seen in several generations
Anticipation
when each subsequent generation of a disease the onset is at an earlier age and more severe with each generation
X-linked recessive:
A "knight's move" pedigree pattern - affected boys may have affected maternal uncles, Parents and children of affected people are normally unaffected. Never transmitted from father to son, Affects mainly males: females can be carriers, and affected males in a pedigree are linked through females, not through unaffected males, Subsequent brothers of affected boys have 1 in 2 risk of being affected; sisters are not affected but have a 1 in 2 risk of being carriers
X-linked dominant:
Features very similar to autosomal dominant pedigrees, except that all daughters and no sons of an affected father are affected, Condition is often milder and more variable in females than in males
Y-linked
A vertical pedigree pattern, All sons of an affected father are affected, Affects only males
Mitochondrial:
A vertical pedigree pattern, Children of affected men are never affected, All children of an affected woman may be affected, but mitochondrial conditions are typically extremely variable even within a family
Factors Influencing Inheritance
Non-penetrance, New mutation, Adult-onset conditions, Consanguinity, Interaction, Sex-limited/Sex influenced, Germline mosaicism, Anticipation, Heterogeneity, Pleiotropy
Autosomal Dominant
Vertical pattern: multiple generations affected, Males and females equally likely to be affected, See male to male transmission, Each child of an affected individual has a 50% chance to be affected, Unaffected individuals do pass on the gene, Every affected child has an affected parent
Autosomal Dominant - Non-Penetrance
An individual who inherits the disease gene does not develop, The disorder appears to "skip" generations
Autosomal Dominant - Sex-Limited/Influenced
Gene expression limited to specific sex, Disorder/trait may appear to "skip" generations
Autosomal Dominant - New Mutation
An alteration occurs in the egg or sperm that made the affected individual (may be first family member to be affected), Recurrence risk for unaffected parents is considered to be low, Risk of new mutation is associated with advanced maternal and paternal age in some disorders (e.g. Achondroplasia)
Autosomal Dominant - Late-onset trait
An individual who inherits the disease gene but does not develop, Examples: Huntington disease, most hereditary cancer syndromes
Autosomal Dominant - Variable Expressivity
Variability of severity of disorder among individuals with same genotype, Examples: Neurofibromatosis, Treacher-Collins syndrome
Heterogeneity - locus heterogeneity
different genes are involved in causing the same phenotype
Pleiotropy
A single locus is responsible for a number of distinct, and seemingly unrelated, phenotypic effects
Autosomal Recessive
Horizontal pattern: single generation affected, Males and females equally likely to be affected, Parents of affected child are unaffected gene carriers and have a 1 in 4 or 25% recurrence risk, Unaffected siblings have a 2/3 or 67% chance to be carriers. Children of affected individuals are obligate carriers
Autosomal Recessive
Increased consanguinity (over general population) is often found between parentsof a child with a rare autosomal recessive disorder, Condition may appear to be dominant in a consanguineous family
X-linked Recessive
Males are more often affected than females, Affected males pass the gene to all of their daughters and none of their sons (NO male-to-male transmission), Daughters of carrier females have a 50% chance to be unaffected, carriers. Sons of carrier females have 50% chance to be affected. Affected males in the family are related to each other through carrier females ("Knight's move")
X-linked Recessive - Other characteristics
For genetically lethal X-linked conditions, 1/3 of isolated cases (i.e. no family history) are new mutations. In 2/3 of cases, the mother is an unaffected carrier. Female gene carriers are usually not affected. Exceptions: Turner syndrome, skewed X-inactivation, X; autosome translocation carriers
X-linked Dominant
For rare conditions, females are about 2x as likely to be affected than males. May be lethal in males and usually milder, but variable, in females. Affected males pass the gene to all of their daughters, who will be affected, and to none of their sons (NO male-to-male transmission). Sons and daughters of affected females have 50% chance of being affected (similar to autosomal dominant)
Y-linked (Holandric)
Only males are affected, Affected males pass the disease gene to all their sons and to none of their daughters
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