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Unit 2 – Pedigrees
• Autosomal recessive inheritance
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All sufferers of the trait are homozygous recessive, e.g. cystic fibrosis.
Men and women are affected in approximately equal numbers.
The trait can skip generations.
The trait is expressed relatively rarely.
Parents of a sufferers may not show the trait if they are heterozygotes.
Individuals which carry the defective allele but are not affected are
called carriers.
– Non-sufferers are homozygous dominant or heterozygote (i.e.
carriers).
• Autosomal dominant inheritance
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Sufferers may be homozygotes dominant or heterozygotes.
– Trait appears in every generation. When a branch of the family tree
does not express the trait, the traits fails to reappear in future
generations.
– Each sufferer of the trait has at least one affected parent.
– Men and women are affected in approximately equal numbers.
– Example: Huntington Chorea
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What’s new?
• http://www.bbc.co.uk/news/scienceenvironment-32932922
http://www.nhs.uk/conditions/huntingtonsdisease/pages/introduction.aspx
• Autosomal incomplete dominance
– Incomplete dominance is when heterozygous individuals have a partly
expressed form, i.e. an intermediate phenotype of the disorder.
– The fully expressed form of the disorder is found in individuals
homozygous for the defective allele.
– The partly expressed form occurs much more frequently than the fully
expressed form.
– The fully expressed form of the disorder occurs rarely.
– Each sufferer of the fully expressed form has two parents who suffer
the partly expressed form of the disorder.
– Men and women are affected in approximately equal numbers.
– Example is sickle cell anaemia
• https://www.dnalc.org/resources/3d/17sickle-cell.html
• Sex linked recessive single gene disorder
• Men will be affected a lot more than women.
• If a normal male and carrier female have a number of children
then they might expect half their daughters to be normal and
half to be carriers; half their sons to be normal and half their
sons to be affected.
• An example of sex linked recessive trait is haemophilia
• http://www.nature.com/nature/outlook/hae
mophilia/#video
• https://www.youtube.com/watch?v=QlkbGSF
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• https://www.youtube.com/watch?v=2pp17E4
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Pre-implantation genetic diagnosis
• How is pre-implantation genetic diagnosis
performed?
• Cells of embryo created using IVF are removed
and screened for specific inherited conditions
Pre-implantation genetic diagnosis
• How is pre-implantation genetic diagnosis
performed?
• Cells of embryo created using IVF are removed
and screened for specific inherited conditions
• What abnormalities can be detected using
PGD?
• Cystic fibrosis, Huntington chorea
• http://guide.hfea.gov.uk/pgd/
• What fertility treatment is PDG often
performed alongside?
• IVF
• Video about new type of screening for IVF
• PGD and designer babies – Ethical issues