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I'm Dr. Simon Holden,
I'm a consultant in clinical genetics in
the Department of Clinical Genetics at Addenbrooke's Hospital in Cambridge,
and I'm also an associate lecturer at the University of Cambridge.
This talk is on recessive inheritance.
Recessive disorders are an important group of Mendelian conditions.
Students will come across them at different stages of their training and for this reason,
it's important that we get to grips with them.
At the end of this lecture,
students should: understand autosomal recessive inheritance;
be able to identify this pattern of inheritance from a family tree;
understand the types of genetic changes in
cell pathways that can be associated with recessive inheritance;
be familiar with some of the more common conditions;
have a knowledge of the factors which can influence the prevalence of
recessive pathological variance (which we also refer to as mutations) within populations;
understand why some recessive disorders can be common and why this matters;
be aware of the importance of carrier frequency and consanguinity when
calculating genetic risk in relation to recessive disorders;
and be able to undertake simple risk calculations,
and describe this pattern of inheritance to a patient.
To start with, it will be useful to go over some genetic jargon.
This will help to orient students and help you get more from the talk.
An allele is a particular genetic change at a given gene locus.
A locus is a position of a gene on a chromosome,
we can think of it as a map coordinate.
A genotype is an individual's genetic constitution at a specified locus or loci.
A phenotype is the clinical effect of an expressed gene or genes.
A heterozygote is an individual with different alleles at a specified locus,
this term is often used to refer to healthy carriers of a recessive condition.
A homozygote is an individual with identical alleles at a specified chromosome locus,
and a compound heterozygote is someone who
has different mutant alleles at a specified locus.