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Summary Human Genetics
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Detailed notes summarising Human Genetics
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BLGY1232 Human GeneticsIncest
Human societies generally (but not always) apply strict taboos on incest This
is because incestuous unions lead to an enhanced likelihood of uncovering
recessive, deleterious alleles, which cause a wide range of inherited disorders
Analysis of children of incest was reported in the British Medical Journal in 1981;
31 children were examined; 13 from the UK and 18 from the US
12 were progeny of father-daughter matings and 19 of sibling matings
2 died shortly after birth
2 subsequently died of recessive disorders
2 surviours suffer from recessive disorders
8 survivors displayed mental retardation
2 displayed congenital malformation
Classification of human genetic disorders
Single gene disorders
Chromosome disorders
Multifactorial disorders
Human genetic disorders
Affect at least 2% of all new-born babies
Account for 50% of all childhood deafness, mental retardation and deaths
Affect 5% of the total population by age 25
Genetic variation imparts of diseases of old age; Alzheimer’s, osteoporosis,
cancer
Identifying genetic causes
We cannot use the techniques traditionally used by geneticists of setting up
backcrosses and sib-sib matings we can’t set up any controlled crosses, and
humans produce too few offspring in order to be suitable subjects for standard
types of analysis (segregation ratios etc)
, We can still interpret patterns of inheritance by applying Mendelian principles.
Locating genes/variations responsible for human phenotypes;
Segregation of hereditary traits studied in families
Family trees drawn to determine mode of inheritance
Statistical association sought between genetic variations and hereditary
traits to locate ‘disease genes’ and gene responsible for other
phenotypes
Pedigree analysis
The tracing of inherited disorders in family trees
Penetrance – percentage of individuals with a particular genotype that express
the phenotype expected of that genotype
Expressivity – degree to which a trait is expressed or variations in the expressed
phenotype
We can recognise certain patterns of inheritance:
Autosomal dominant
Gene carried on an autosome, a dominant allele is responsible for
the condition
Huntington’s disease, Myotonic dystrophy, Polydactyly, Brittle
bone disease, early onset Alzhemier’s + >3160
An affected person usually has one affected parent
Affects either sex
Transmitted by either sex
A child of an affected x unaffected mating has 50% chance of
being affected
Autosomal dominant conditions are passed on by either sex, and
if you carry the dominant allele, you will develop the condition
Not all autosomal dominant conditions show full Penetrance
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