HUMAN CHROMOSOMES Chapter 14-2 Genes located on sex chromosomes follow different patterns of heredity.  Males are more likely to be affected by these genes. 

GENES ARE LOCATED ON CHROMOSOMES   Some genes are located on the SEX CHROMOSOMES  ( X and Y) Genes on the X chromosome may affect boys different from girls These are called SEX-LINKED GENES

EXAMPLES: SEX LINKED GENES Coat color in cats:  Black, Orange,  Calico   X B X B  = black, female X O X O = orange, female X B X O = calico, female X B Y  = black, male X O Y  = orange, male REMEMBER:  THE Y IS WIMPY!  No letters (genes) are attached to it.

X B X B (black female) x X O Y (orange male) CROSSES   X B X B  (black female)      x     X O Y  (orange  male)  This explains why all calico cats are female! ALSO:  in any given cell, one of the X's becomes inactive, which randomizes the pattern or orange and black

COLORBLINDNESS IS ALSO SEX LINKED Look what happens when a woman who is a CARRIER (b) marries a normal man (B) X B X b     x      X B Y What happens when a colorblind man marries a normal woman? X B X B     x      X b Y

COLORBLIND TEST

Young children are given pictures instead of numbers

HEMOPHILIA  - "bleeder's disease" Blood will not clot normally, small injuries can be life threatening Females can be carriers:  

What happens if Mom is a carrier?

DUCHENNE MUSCULAR DYSTROPHY - causes progressive weakening and loss of muscle tissue Females can be carriers:                          X D X d