Inheritance Patterns

1. 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 monosomic trisomic

2. 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

3. 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

4. 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

5. Exceptions to Mendeliangenetics • 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