CREDITS Animation & Design: Chloe Fyvie Adams
Narration: Dale Bennet
Script: Gemma Young
This girl has six fingers on her left hand. She has a condition called polydactyly, which causes extra fingers or toes. Her father and grandmother as well as some of her cousins also have the condition. This should give you a clue about how she came to have it... any ideas?
Well, polydactyly is an example of a genetic disorder - it is inherited.
You inherit genes from your parents, and you have two copies of each gene - one from your mother and one from your father.
Genes come in different forms, called alleles. Alleles may be recessive or dominant.
So going back to Polydactyly…
Polydactyly is caused by a dominant allele, shown as a capital P. You only have to have one copy of this allele to have the condition. So in an example the father has a copy of this allele, but the mother does not…
Offspring with one dominant allele big P, and one recessive allele little p will also have the condition.
Whereas these offspring won’t have the condition. Can you see what their genotype must be...?
Little p, little p - so two copies of the recessive allele.
Another example of an inherited disorder is cystic fibrosis. If you want to discover more about cystic fibrosis, and how it affects the body then watch this video [insert link to ‘cystic fibrosis’ video].
Cystic fibrosis is inherited in a different way to polydactyly. Take a look at this genetic diagram and see if you can figure out how it is different.
To have cystic fibrosis, you have to inherit two recessive alleles. The parents in the diagram are both carriers of the recessive allele, little f. They do not have the disorder themselves but they could both pass the recessive allele to their children.
Quite often, people do not know they are carriers of cystic fibrosis until they have a child with the disorder. This can be very upsetting, as it is a serious condition.
Parents are able to make sure they do not have another child with the disorder using embryo screening.
Let’s finish off with a little discussion about what embryo screening is.
Embryo screening can be used to ensure embryo’s do not suffer from inherited genetic disorders.
To do this, the parents would use in-vitro fertilisation, which is also known as IVF.
IVF is where eggs and sperm are mixed in a dish in a lab outside of the body. Each fertilised egg would be left to grow until it reached a few cells big, and then one cell from each embryo is removed and its genes tested to see if it has the genetic disorder. Only unaffected embryos - a maximum of two - would be placed back into the mother’s uterus to grow and hopefully develop into a healthy baby.
There are many issues surrounding embryo screening. One ethical issue is that the unused embryos, potential lives, are destroyed. Also, there are social concerns - IVF is not always successful and this can be upsetting for the parents and their family. Finally there are also economic issues because IVF is an expensive process.
So there we have a few examples of inherited genetic disorders. These are inherited from your parents, resulting from certain alleles your parents have been carriers of.
Sometimes genetic disorders are caused by dominant alleles - like polydactyly so it can be inherited from one parent - and others are caused by recessive alleles - like cystic fibrosis - so both parents need to carry the allele.
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