Inheritance Patterns Things that cause alterations in chromosome number or pattern lead to genetic disorders. – Alterations in chromosome number - aneuploidy caused by nondisjunction – failure of a chromosome to separate during meiosis » if nondisjunction is of a single chromosome the zygote will either be monosomic or trisomic » if nondisjunction is of a entire genome the zygote will exhibit popolyploidy Triploidy, tetraploidy, … Very common in plants but not viable in animals monosomictrisomic

Examples of Syndromes Associated with Non-disjunction – monosomic - Turner Syndrome (XO) only viable monosomic disorder in humans 1/500 births sterile, less developed secondary sex characteristics (better with estrogen therapy) – trisomic Down Syndrome (trisomy 21) – 1/700 births – part of the pre-birth screening panel – short stature, heart defects, prone to respiratory infections, mental retardation – risk increases dramatically for childbearing women over the age of 30 XXX – Normal outwardly – 1/1000 births XXY – Klinefelter syndrome – under developed genitalia – sterile – some female sex characteristics - fleshy breasts – 1/2000 live births XYY may be taller but otherwise indistinguishable

Alteration in Chromosome Structure homologous alterations - often lethal – deletion can cause a frame-shift affecting all genes down stream cri du chat syndrome – deletion in chromosome 5 – cry sounds like a mewing cat, microcephaly, retardation, death in early childhood – duplication Caused by the attachment of a deleted region during meiosis Causes gene dosing errors – inversion Reverse attachment of a deleted region during meiosis Causes reading frame errors in genes

– non-homologous alterations translocation – attachment of a deleted region from a non-homologous chromosome – reciprocal translocations occur when neighboring chromosomes cross over » gene number is conserved although gene dosing secondary to gene position may be affected – implicated in many cancers and leukemia

Exceptions to Mendelian genetics Genomic imprinting – effect of the depends on the sex of the person inherited from – occurs during the formation of gametes – certain genes are turned off in the sperm & the ova insulin-like growth factor (used in prenatal growth) – only the paternal version is expressed Inherited organelle genes (extranuclear genes) – circular DNA found in the mitochondria and chloroplasts – inherited in the cytoplasm of the ova (maternal) – mitochondrial myopathy weakness, intolerance of activity, muscle deterioration