More Inheritance 3.4 continued

Traits carried on sex chromosomes I. Sex-linked Traits Traits carried on sex chromosomes Mostly on X, very few on Y X and Y are not homologous – do not carry the same genes a. This means females have 2 copies of genes carried on the X chromosome while males only have 1 copy 3. Traits represented as superscripts on the X

Because females have two copies, they can be carriers of recessive sex-linked traits (XHXh) 1. If a son receives the recessive allele from mom, he has the recessive trait because he received a Y from dad (XhY) 2. If mom is a carrier, sons have a 50/50 chance of having the trait 3. In order for females to inherit the trait, their father must have the trait

Common Sex-linked traits 1. Color-blindness 2. Duchene muscular dystrophy 3. Calico fur color in cats 4. Hemophilia

II. Pedigrees Used to track traits over generations in a family 1. Circle = females, Squares = males 2. Vertical lines = children, Horizontal lines = “married” 3. Shaded in = expresses the trait being tracked, not shaded in = doesn’t express the trait

Often used to track sex-linked traits

C. Can be used to deduce mode of inheritance (ex C. Can be used to deduce mode of inheritance (ex. Is it a dominant or recessive trait?)

III. Causes of mutations, genetic diseases, and cancer Mutagens – external factors that induce mutations Chemicals, radiation, X-rays, etc. – knock out DNA bases Carcinogens – mutagens that change genes involved in the control of the cell cycle Chernobyl Hiroshima Marie Curie