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Pedigree Clues Published on LaraSig (https://www.larasig.com) Pedigree Clues [1] Description: Pedigree Clues Autosomal Dominant Characteristics of autosomal dominant inheritance (exceptions to these rules may occur due to de novo mutations, variable expressivity, reduced penetrance or sex-limited expression): Males can transmit the condition to males (father to son). Males and females are equally likely to transmit the condition (to children of either gender). Males and females are both affected, usually in equal proportions (if there are enough people in the pedigree). The condition appears in multiple successive generations (vertical inheritance pattern). Each child of an affected parent has a 50% chance of being affected, provided the other parent is unaffected. Thus, half of the children of an affected individual are affected on average (may vary considerably due to statistical chance). Unaffected individuals do not have affected children. Some characteristics of autosomal dominant disorders include: The condition may have a late age of onset. Conditions often exhibit variable expressivity and/or reduced penetrance. Therefore, they may appear to skip generations; or severely affected children can be born to a parent so mildly affected that the affected parent was previously unrecognized. The condition may result from a new mutation. Thus, a single affected individual in the pedigree does not rule out autosomal dominant inheritance (the first affected individual's children would still have 50% risk for being affected). A homozygous state for the condition may result in being more severely affected, or it may be lethal. Ethnicity and consanguinity are not important factors in disorder frequency as they are in autosomal recessive inheritance. Page 1 of 5 Pedigree Clues Published on LaraSig (https://www.larasig.com) Autosomal Recessive Characteristics of autosomal recessive inheritance: Typically, unaffected parents have affected children. Males and females are both affected, usually in equal proportions (if there are enough people in the pedigree). The condition usually appears in a single sibship, unless carrier frequencies are high (horizontal inheritance pattern). Each full sibling of an affected individual has a 25% chance of being affected. Thus, one quarter of the children in a sibship are affected on average (may vary considerably due to statistical chance). Conditions are more common among parents who are closely related (consanguineous), especially for rare conditions. Some characteristics of autosomal recessive disorders include: Conditions often have an early age of onset (infancy to childhood). Conditions may be more common in certain ethnic groups. Disorders may be inborn errors of metabolism. The first case may not be recognized as genetic. Conditions are less likely to exhibit variable expressivity and/or reduced penetrance than autosomal dominant ones. X-Linked Recessive Characteristics of X-linked recessive inheritance: Males are exclusively or much more commonly affected than females. Females are typically unaffected carriers. However, if females do exhibit clinical symptoms, findings are often more mild than for males. Affected males have unaffected children (provided the mother is not a carrier). No sons inherit the condition (they inherit the Y chromosome), and all daughters are carriers (they inherit the affected X chromosome). Unaffected males do not transmit the condition to their children. Carrier females do not have affected daughters (provided the father is unaffected). Affected males are related to each other through unaffected carrier females. Page 2 of 5 Pedigree Clues Published on LaraSig (https://www.larasig.com) The sons of carrier females have a 50% chance of being affected, and daughters have a 50% chance of also being carrier females. Thus, half the sons in an affected sibship are affected on average (although there may be significant variation due to statistical chance). Some characteristics of X-linked recessive disorders include: Females who exhibit symptoms often have skewed X inactivation. Sex chromosome abnormalities (45,X; 47,XXY) can alter expected inheritance patterns based on gender. New mutations are relatively common. Therefore, females are only considered obligate carriers if they have 2 affected sons and/or an affected son and another affected male relative. For common X-linked recessive disorders (such as color blindness) or rarely with consanguinity, inheritance may not follow typical patterns because both mother and father may have a gene mutation. Ethnicity and consanguinity are typically less important factors in disorder frequency than they are in autosomal recessive inheritance. X-Linked Dominant Characteristics of X-linked dominant inheritance (assumes only one parent has a gene mutation): Males and females may be affected. Affected males are typically more severely affected than affected females. Affected males transmit the condition to none of their sons and all of their daughters. Affected females can have affected daughters or sons. Each child of an affected female has a 50% chance of being affected (son or daughter), provided the other parent is unaffected. Some characteristics of X-linked dominant disorders include: Condition may be lethal in males, leading to fewer than expected males in the pedigree or a history of multiple pregnancy losses. Disorders with this inheritance type are rare. Mitochondrial Page 3 of 5 Pedigree Clues Published on LaraSig (https://www.larasig.com) Characteristics of mitochondrial inheritance: Males and females are both affected, usually in equal proportions (if there are enough people in the pedigree). Only females transmit the condition to their children (no father-child transmission). All affected individuals are related to each other through females (may be affected or unaffected). The condition appears in multiple generations. Some characteristics of mitochondrial disorders include: Conditions may exhibit extreme variable expressivity. Affected individuals may not exhibit symptoms (reduced penetrance). Disorders may be degenerative and involve central nervous system symptoms. Chromosomal Characteristics of chromosomal inheritance: Can mimic virtually any inheritance pattern due to the many different origins and types of chromosome abnormalities. Some characteristics of chromosomal disorders include: Best identified by cytogenetic testing based on clinical findings such as the following: Combinations of major and/or minor congenital anomalies Mental retardation with or without major/minor anomalies Recurrent pregnancy loss Sexual development disorders (e.g., ambiguous genitalia, primary amenorrhea, delayed puberty) Infertility Stillbirth or infant death field_vote: Page 4 of 5 Pedigree Clues Published on LaraSig (https://www.larasig.com) Product: genetics [2] Tags: chromosomes [3] Topics: genetic abnormalities [4] Resource Type: document [5] Source URL: https://www.larasig.com/node/2064 Links: [1] https://www.larasig.com/node/2064 [2] https://www.larasig.com/taxonomy/term/16 [3] https://www.larasig.com/category/tags/chromosomes [4] https://www.larasig.com/category/topics/genetic-abnormalities [5] https://www.larasig.com/category/resource-type/document Page 5 of 5