lethals genes which cause death of the organism

pleiotropy Single gene affects many traits, even seemingly unrelated ones

epistasis One non-allelic gene pair masks another -- from Greek, “standing upon” (much like dominance)

collaboration Two non-allelie gene pairs produce novel phenotype (much like incomplete dominance)

Polygenic traits 2+ non-allelic gene pairs that control a single trait

penetrance % individuals who show phenotype expected from genotype

expressivity degree to which a particular gene is expressed in an individual

Effects of the environment environment affects gene expression environmentally-produced phenotype which mimics genotype = phenocopy

Linkage Lack of independent assortment of genes due to location on the same chromosome

Recombination Breaks in linkage and transmission of new gene combinations on a single chromosome after prophase I crossovers

Mapping Using crossover frequencies as relative map units – allows construction of “maps” of gene locations

Karyotype

Causes of Genetic Diseases *aneuploidies from nondisjunctions

Down’s syndrome

Edward’s syndrome trisomy 18 Patau’s syndrome trisomy 13

sex chromosome aneuploidies

*abberations

fragile-X syndrome

*point mutations: single gene disorders

dominant autosomal

Huntington’s disease (chorea)

Marfan’s syndrome (arachnodactyly)

Neurofibromatosis (Elephant Man’s disease)

Amyotropic Lateral Sclerosis (Lou Gerhig’s Disease)

incomplete dominant autosomal

Acondroplasia (dwarfism)

Tay Sachs Disease

Sickle Cell Anemia

Cystic Fibrosis

Hypercholesterolemia

recessive autosomal

PKU: Phenylketonuria

hemachromatosis Albinism Fanconi’s anemia Cooley’s anemnia

sex-linked

hemophilia

Duchenne muscular dystrophy

colorblindness

Lorenzo’s Oil disease (adrenoleukodystrophy) Retinitis pigmentosa Lesch-Nyhan disease

Other genetic diseases Tourette’s syndrome Schizophrenia Colon cancer Alzheimer’s (one form) Depression (one form) Diabetes (one form) Dyslexia

Pedigrees

Genomic Imprinting