powerpoint presentation: pedigree charts

PEDIGREE CHARTS

A family history of a genetic condition

© 2016 Paul Billiet ODWS

http://www.saburchill.com/IBbiology/bio_hp.html

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.



Studying human genetics

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.



Symbols used in pedigree charts

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



Organising the pedigree chart

A pedigree chart of a family showing 20 individuals.




Generations are identified by Roman numerals. I

II

III

IV© 2016 Paul Billiet ODWS



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



If two affected individuals give rise to an unaffected child the affected condition is dominant

So roller allele is dominant (R) and non-roller allele is recessive (r).



Tongue rolling



Tongue rolling

rr

rr

rrrr

rr



Tongue rolling

All non-rollers must be genotype rr



Tongue rolling

rr

rr

rrrr

rr



Tongue rolling

rr

rr

rrrr

rr Rr

Rr

Rr

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.



Tongue rolling

Unfortunately people can learn to roll their tongues too.


Albinism


Albinism

aa aa aa aa

aa

Aa AaAaAa

Aa AaAa


Albinism - a recessive condition 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.


Polydactyly


Dominant conditions

If two affected parents have an unaffected child the allele for the affected condition is dominant.


Brachydactyly


powerpoint presentation: pedigree charts

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