KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

Sexually reproducing organisms have two of each chromosome. One from mother and one from father Have the same genes, but may have different alleles About 99.9% of all human DNA is identical

Autosomal genetic disorders: disorders that have no relation to the sex of an individual Autosomal recessive disorder: Any offspring with two recessive genes (cc) will have the disease/disorder A carrier is heterozygous (Cc) for a recessive disorder C c CC Cc Ex: Cystic Fibrosis C *carrier c Cc cc *carrier Disorder

Albinism is a autosomal recessive disorder characterized by a lack of pigment I skin, hair and eyes.

A a A a A a Fill out these punnett sqs. What is the probability that the offspring will have albinism?

A a A a A a AA Aa Aa aa AA Aa Aa aa O% will have albinism 50% carriers Both Mom and Dad have to either have the disorder or be carriers for offspring to be affected with an autosomal recessive disorder!

Autosomal Dominant Disorders: any offspring showing a dominant allele will have the disorder Dominant disorders are uncommon Ex: Huntington’s Disease H h Hh hh h *anywhere there is an H the child will have the disease Disorder Hh hh h Disorder

Genes on sex chromosomes are called sex-linked genes. Y chromosome genes in mammals are responsible for male characteristics. X chromosome genes in mammals affect many traits.

Male mammals have an XY genotype. All of a male’s sex-linked genes are expressed because Males have no second copies of sex-linked genes. One copy X, one copy Y

Female mammals have an XX genotype. Expression of sex-linked genes is similar to autosomal genes in females. X chromosome inactivation randomly “turns off” one X chromosome ensures that females, like males, have one functional copy of the X chromosome in each body cell X

Males only have one X chromosome so one color will be present (recessive OR dominant) Female cats have two X chromosomes. Each patch of fur can be different depending on which X chromosome “turns off”