Constructing a Gene MapThe farther two genes are from each other, thehigher the probability that crossing over will occurbetween them. This can be used to figure outwhere genes are on the chromosome.
Genetic disorders caused by abnormal chromosome number (due to nondisjunction)Name Chromosome DescriptionDown syndrome 21 TrisomyEdward’s syndrome 18 TrisomyPatau syndrome 13 TrisomyTurner’s syndrome Single X XOKlinefelter’s syndrome Extra X (in males) XXYXYY syndrome Extra Y (in males) XYYTriple X syndrome Extra X (in females) XXX
Genomic Imprinting• Some genes behave differently if they come from ova/ sperm• One gene can be “silenced” and the other is expressed• Imprinting is not inherited• Genes are re-imprinted for in the next generation
Example: Imprinting• Prader-Willi/ Angelman syndromes• Deletion on chromosome 15• If inherited from father – Prader-Willi syndrome • Mental retardation, obseity, short stature, small hands and feet• If inherited from mother – Angelman syndrome • Spontaneous uncontrollable laughter, jerky movements, motor and mental problems