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OUTLINE 14 VI. Extensions to Mendel’s Rules (continued) D. Sex Linked Inheritance 1. Sex chromosomes 2. Systems of sex determination a. XY system b. X0 systems c. ZW systems d. Haplo-diploid systems e. Non-chromosomal sex determination 3. X-linked inheritance
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OUTLINE 14 VI. Extensions to Mendel’s Rules (continued) D. Sex Linked Inheritance 1. Sex chromosomes 2. Systems of sex determination a. XY system b. X0 systems c. ZW systems d. Haplo-diploid systems e. Non-chromosomal sex determination 3. X-linked inheritance 4. Y-linked inheritance
Application of Mendel’s Rules assumes: • 1. One allele completely dominates the other • 2. All genes have 2 allelic forms • 3. All traits are monogenic (affected by only one • locus) • 4. All chromosomes occur in homologous pairs • 5. All genes assort independently • 6. An allele is completely expressed when either • dominant or homozygous • 7. Each trait is controlled by a different set of factors
Human Genome Autosomes (1 – 22) Sex Chromosomes (X and Y)
X Y
Human Y-chromosome SRy locus
XY sex determination In some plants
Drosophila melanogaster Ratio of X to autosomal: Female: 1 set autosomes : 2X Male: 1 sets autosomes : 1X XX = female Both XY or X_ = male
Environmental control Alligators Turtles
X Y
Colorblindness: Alleles: X+ = normal vision, Xc = color blind (X+ is dominant) phenotypes female genotypes male genotypes normal X+X+X+ Y color blind XcXcXc Y carrier*X+Xc * carrier - transmits but does not express a trait
Female’s gametes Xc Xc X+ Male’s gametes Y
X-linked inheritance: Fur color mosaics in female cats Fig. 15.10