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Pedigree Clues
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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.
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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.
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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
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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
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Pedigree Clues
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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
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