1. Patterns of Inheritance #2
Gene Addresses
Patterns of Inheritance #2

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

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

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

5. Marking the Locations

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

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

10. Hair: 2 p* (*hypothetical location)
Codominant Genes
Blood Type: 9 q
P53 Cancer gene: 17 p
Hair: 2 p* (*hypothetical location)

11. N D

12. Polygenic Traits
Many genes
On different chromosomes
Eye color
Height

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

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

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

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

17. Color Blindness XN XN XNY normal XN Xcb Xcb Xcb XcbY color blind
Genotypes: Phenotype
XN XN
XNY normal
XN Xcb
Xcb Xcb
XcbY color blind

18. Cross: XNXcb x XNY Phenotypic ratio: 2: 0: 1: 1 female to male
XN XN XN Xcb
XNy xCB y
Phenotypic ratio: 2: 0: 1: 1
female to male
Genotypic Ratio: 1:1:1:1

19. Pedigree

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

21. XNXN x XhY XN XN Phenotypic Ratio: 2: 0: 2: 0
XN Xh XNXh
XNY xN y Xh Y
Phenotypic Ratio: 2: 0: 2: 0
Genotypic Ratio: 0: 2: 2: 0

22. Pedigree