Pedigree Analysis Flashcards
Pedigrees
Used for tracking genes through generations, defining inheritance patterns, symbols show sex and genetic status, lines show descent and relationships
Pedigree symbols
Square- male, circle- female, diamond- unknown
Horizontal connect lines
Connects spouses
Vertical lines
Lead to offspring
Horizontal connector lines
Siblings
Y-shaped connector
Used for twins, identical twins have a crossbar
Double horizontal line
Consanguineous matings
Filled symbol
Affected individuals (have the disease)
Half-filled symbol
Known carriers of the disease
Dot in the symbol
X-linked carrier (will not always be indicated in the pedigree)
Slash through symbol
Deceased individuals, only done in small pedigrees
Consanguinity
Mating of genetically related individuals, uncommon in Western countries, relatives often share common genes from ancestor, can be gene for recessive disorder
Coefficient of relationship
Expression of probability of sharing a common gene from an ancestor, essentially 50% for each generation
Probability of siblings sharing a gene
1/2 probability
Probability of first cousins sharing a gene
1/8 probability
Probability of second cousins sharing a gene
1/32 probability
Consanguinity and probability
The rarer the recessive disorder, the more likely the parents are consanguineous
X-linked dominant pedigree
More females affected, no father-son transmission, all daughters of affected males are affected
X-linked recessive pedigree
Females more likely to be carriers, if males get one copy of the allele, they get the disease
