Gene Addresses Patterns of Inheritance 2 Genetic Loci

Gene Addresses Patterns of Inheritance #2

Genetic Loci (Address) n. Must have a way to identify the location of a certain gene n. Use “address system” to describe the location of a gene on a chromosome

Locating the Genes Example: 4 p 1 6 n 4: chromosome n. P: top half n 1: first section from centromere n 6: 6 th band in the section (our diagrams are not detailed enough to be very specific)

Example: Huntington’s Disease n n Found at one end of chromosome 4 Actual address used by geneticists worldwide is: 4 p 1 6

Marking the Locations

Locations of Dominant Genes Huntington’s Disease: 4 p Marfan’s Disease: 17 q Widow’s peak: 1 p* (*hypothetical location)

Recessive genes Cystic Fibrosis: 7 q Tay Sach’s disease: 15 q Cleft Chin: 5 q* (*hypothetical location)

Codominant Genes Blood Type: 9 q P 53 Cancer gene: 17 p Hair: 2 p* (*hypothetical location)

N D

Polygenic Traits Many genes n On different chromosomes n n Eye color Height n

Height n n Each capital letter will add 2” to the base height. Female base height: 5’ 0” Male base height: 5’ 4” Example: Genotype: Aa. Bb. CC dd Phenotype: 5’ 8” for female 6’ 0” for male

Locations for Height Genes n n 13 q: 14 q: 16 p: 18 q: A B C D

X-Linked Traits n n Genes located on the X chromosome Females receive two alleles Males receive one allele Males more likely to express trait

X-linked Example: Color Blindness n n Cannot distinguish between red and green Symbols XN: normal allele Xcb: recessive allele for color blindness Address: Xq 2 6

Color Blindness n Genotypes: Phenotype XN XN X NY normal XN Xcb Xcb. Y color blind

Cross: XNXcb XN n x Xcb XN XN Xcb Y X Ny x. CB y Phenotypic ratio: 2: 0: 1: 1 female to male n X NY Genotypic Ratio: 1: 1

Pedigree

Hemophillia n n Blood does not clot correctly Symbols XN: normal allele Xh: recessive allele for hemophillia Address: X q 2 8

X NX N XN Xh Y n n XN X h X NY x X h. Y XN X NX h x. N y Phenotypic Ratio: 2: 0 Genotypic Ratio: 0: 2: 2: 0

Pedigree