Melanie Pritchard; Week 4 MED1011; Biochemistry
Females are circles, males are squares on pedigrees. An arrow is used to identify the proband (that who first presented with the condition). Single gene disorders are known as Mendelian disorders.
Alleles are different versions of genes. They may be homozygous or heterozygous. The genotype refers to individual's genetic makeup at its locus, any gene determined characteristic is a trait, phenotype is physical appearance.
Patterns of inheritance are autosomal dominant, autosomal recessive, X-linked.
Autosomal dominant inheritance is characterised by equal numbers of affected males and females, vertical transmission without skipped generations, every affected person must have at least one affected parent, affected fathers can have affected sons.
Autosomal recessive disease is usually rare, haemoglobinopathies are more common. Sex linked inheritance is confined to X linked disorders, most are recessive (so are more common in males). Males have 1 copy of X gene so are hemizygous. Early in embryonic development one of the female X chromosomes is deactivated (lyonisation which involves heavy methylation and supercoiling). Inactivation is random between maternal and paternal and inactivation is inherited through cell lines. They are mosaics for 2 X chromosome populations. Daughters who are heterozygous are carriers. Generations can be skipped. If an affected male has children all his daughters will be carriers. In autosomal dominant, an affected male transmits the disease to all his daughters.
Life (9th) 236-250