Yellow dots mark the locus of a specific gene on a homologous pair of human chromosomes CHAPTER 14 THE HUMAN GENOME

The chromosomal basis for Mendel’s Laws

Sex-linked inheritance

Evidence for linked genes in Drosophila

The transmission of sex-linked recessive traits Sex-linked traits in humans include red-green color blindness hemophilia, and Duchenne muscular dystrophy

X inactivation and the tortoiseshell cat. The tortoiseshell gene is on the X chromosome and the phenotype requires the present of both alleles (one on each X chromosome) In each cell, one X is coiled up and condenses to form a Barr body

Meiotic nondisjunction

Nondisjunction-results in an extra or missing chromosome, most embryos die and spontaneously abort XO-Turner Syndrome only human monosomy that survives, sterile, petite, female who is mentally normal XXY-Klinefelter Syndrome-sterile male with some female characteristics, mentally gifted in some areas and slow in others XYY-super male, normal physically and mentally but prone to violence XXX & XXXX-super female normal physically and mentally but prone to violence Trisomy 21-Down syndrome-can also be caused by translocation of part of chromosome 21 mentally slow are fertile