05PEDIGREE CHARTS

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PEDIGREE
CHARTS
A family history of a genetic condition
© 2016 Paul Billiet ODWS
What is a pedigree chart?



A record of the family of an individual
Used to study the transmission of a
hereditary condition
Useful when there are large families and a
there is a good family record over several
generations.
© 2016 Paul Billiet ODWS
Studying human genetics

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You cannot make humans of different types
breed together
Pedigree charts offer an ethical way of studying
human genetics
Today genetic engineering has new tools to
offer doctors studying genetic diseases
A genetic counsellor will still use pedigree charts
to help determine the distribution of a disease in
an affected family.
© 2016 Paul Billiet ODWS
Symbols used in pedigree
charts

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Normal male
Affected male
Normal female
Affected female
Marriage.
A marriage with five children, two
daughters and three sons. The middle
son is affected by the condition
Eldest child  Youngest child
© 2016 Paul Billiet ODWS
Organising the pedigree
chart

A pedigree chart of a family showing 20
individuals.
© 2016 Paul Billiet ODWS
Organising the pedigree
chart

Generations are identified by Roman
numerals.
I
II
III
IV
© 2016 Paul Billiet ODWS
Organising the pedigree
chart


Individuals in each generation are identified by Arabic
numerals numbered from the left
Therefore the affected individuals are II3, IV2 and IV3.
I
II
III
IV
© 2016 Paul Billiet ODWS
Tongue rolling
© 2016 Paul Billiet ODWS

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If two affected individuals give rise to an
unaffected child the affected condition is
dominant
So roller allele is dominant (R) and nonroller allele is recessive (r).
© 2016 Paul Billiet ODWS
Tongue rolling
© 2016 Paul Billiet ODWS
Tongue rolling
rr
rr
rr
rr
rr
© 2016 Paul Billiet ODWS
Tongue rolling

All non-rollers must be genotype rr
© 2016 Paul Billiet ODWS
Tongue rolling
rr
rr
rr
rr
rr
© 2016 Paul Billiet ODWS
Tongue rolling
rr
Rr
rr
Rr
Rr
rr
rr
Rr
© 2016 Paul Billiet ODWS
Rr
Rr
rr
Tongue rolling


If one of the parents is a roller and the
other is a non-roller all the roller children
must be heterozygous rollers (Rr)
If a roller parent has a non-roller child
the parent must be heterozygous.
© 2016 Paul Billiet ODWS
Tongue rolling
Unfortunately people can learn to roll their
tongues too.
© 2016 Paul Billiet ODWS
Albinism
© 2016 Paul Billiet ODWS
Albinism
aa
Aa
Aa
Aa
aa
Aa
Aa
Aa
aa aa
Aa
aa
© 2016 Paul Billiet ODWS
Albinism - a recessive
condition
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If two unaffected individuals give rise to
an affected child, the allele for the
affected condition is recessive
The unaffected parents are carriers
(heterozygous)
Thus recessive conditions can skip
several generations
Inbreeding increases the chance of
carriers producing an affected child.
© 2016 Paul Billiet ODWS
Polydactyly
© 2016 Paul Billiet ODWS
Dominant conditions

If two affected parents have an unaffected child
the allele for the affected condition is dominant.
© 2016 Paul Billiet ODWS
Brachydactyly
© 2016 Paul Billiet ODWS
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