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useful information for those trying to work out what is happening in a pedigree chart
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Affected Not affected
Female
Male
The idiots guide to pedigree charts
Key to alleles
D = dominant allele
d = recessive allele
XD = dominant allele on the X chromosome
Xd = recessive allele on the X chromosome
Y = Allele not carried on the Y chromosome
Key to pedigree charts
Chris Paine h?ps://bioknowledgy.wikispaces.com/
gametes D d
D DD Dd
d Dd dd
A
B
A B Disease caused by a dominant (D) allele
look for two affected parents producing a normal individual
Chris Paine h?ps://bioknowledgy.wikispaces.com/
gametes D d
D DD Dd
d Dd dd
A
B
A B
look for two unaffected parents producing an affected individual
Disease caused by a recessive (d) allele
Chris Paine h?ps://bioknowledgy.wikispaces.com/
Disease caused by a dominant (D) allele
in dominant diseases usually more than 25%, by probability 50% of individuals in a pedigree chart will be affected
Chris Paine h?ps://bioknowledgy.wikispaces.com/
Disease caused by a recessive (d) allele
In recessive diseases affected individuals oQen occur every other generaRon
Chris Paine h?ps://bioknowledgy.wikispaces.com/
Disease is sex-‐linked (carried on the X chromosome)
most if not all affected individuals will be male
Chris Paine h?ps://bioknowledgy.wikispaces.com/
gametes Y Xd
XD Y XD XDXd
Xd Y Xd XdXd
A
B
B A
Disease is sex-‐linked (carried
on the X chromosome)
females maybe affected, but only if the male parent is affected
Chris Paine h?ps://bioknowledgy.wikispaces.com/