BIOL 2030 Lecture Notes - Lecture 7: Adenosine Deaminase Deficiency, Brachydactyly, Mendelian Inheritance
7 – Pedigree Analysis and Applications
January 18th, 2016
Mendelian Genetics in Humans
The inheritance of genes follows the same principles in all sexually reproducing eukaryotes
• Controlled matings: no
• Generation time: ~6200 days
• Family size: ~2.1
• Separating genetic and environmental factors: twin & adoption studies
*Need unique techniques: pedigree analysis and twin/adoption studies
The first genetic trait identified in humans was brachydactyly (1905) by analyzing pattern of
transmission of the trait in families pedigree analysis
• Study of family tree comprising of individuals that clearly exhibit trait
• Proband is the affected individual…
Pedigree: a standardized pictoral representation of a family tree that portrays the inheritance of
one or more characteristics *see legend
• Ex. Waardenburg syndrome
o Trait appears ine very generation
o Trait seems to affect males and females equally
o All affected offspring have at least one affected parent
Autosomal Recessive Traits
• Large number of human traits caused by homozygosity for mutant alleles, including
many serious abnormalities or diseases
• Recessive mutant alleles produce mutant phenotype: loss of function or a modified
function
• Disorders:
o Adenosine deaminase deficiency
o Albinsism
o Cystic fibrosis
o PKU
• Inheritance:
o Affected often born to unaffected
o Heterozygous parent cross produce about ¼ affected offspring
o When both parents are affected, the trait will appear in ALL offspring
o Appear equally between males and females
o Tends to skip generation
o More likely to appear among a progeny of related parents (incest)
find more resources at oneclass.com
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Document Summary
The inheritance of genes follows the same principles in all sexually reproducing eukaryotes: controlled matings: no, generation time: ~6200 days, family size: ~2. 1, separating genetic and environmental factors: twin & adoption studies. *need unique techniques: pedigree analysis and twin/adoption studies. Pedigree: a standardized pictoral representation of a family tree that portrays the inheritance of one or more characteristics *see legend: ex. Waardenburg syndrome: trait appears ine very generation, trait seems to affect males and females equally, all affected offspring have at least one affected parent. Sex linked traits: genes for at least 100 traits on the x chromosome, few genes have been identified on the y chromosome, types, x-linked recessive, ex. Inheritance: only males are affected, does not skip generations. Penetrance: % individuals having a particular genotype and expressing specific phenotype. Expressivity: degree to which a character is expressed. *incomplete penetrance and variable expressivity are due to effects of other genes and environmental factors.
