Humans have 23 pairs of chromosomes One pair

• Humans have 23 pairs of chromosomes. • One pair of chromosomes is related to the sex of an individual , these chromosomes are called sex chromosomes

• The other 22 pairs of chromosomes are called autosomes (1 -22)

• Genes that are located on the X chromosome are called sex-linked genes. • Traits determined by sex-linked genes are called sex-linked traits (c = colorblind, C = normal) Ex. Color blindness female Xc Xc male Xc Y

• Sex linked traits are recessive, this means both x chromosomes must have the gene in order for the trait to be expressed.

• If only one x chromosome is present (in males)and has the sex linked gene, then the trait will be expressed

• A carrier is a person that has the trait on only one chromosome and does not express the trait. Carriers of sex linked traits are always women. (C= normal, c= colorblind) Ex. Color blind carrier XC Xc

• A colorblind male marries a normal female. What are the offspring genotypes and phenotypes? (C = normal, c = colorblind) Xc XC XC Y

• A normal male (not colorblind) marries a carrier. What are the offspring genotypes and phenotypes? XC Y XC Xc

• A normal male (not colorblind) marries a colorblind female. What are the offspring genotypes and phenotypes? XC Y Xc Xc

• Hemophilia is characterized by uncontrolled bleeding • It is a sex linked disorder caused by errors in the DNA that codes for the proteins involved in clotting

Linked Genes • Some traits seem to be inherited together. – Example Gray bodied fruit flies also have long wings. Genes that tend to be inherited together are on the same chromosome and called Linked Genes.

Mutations • Germ-Cell Mutations are changes in your sex cells. They do not affect the person, but can be passed on. • Somatic- Cell Mutations are changes to your body cells and can affect you.

Mutations • A Chromosome Mutation is a change in the structure of a chromosome or the loss or gain of a chromosome. • Four main types of mutation. – Deletion – Inversion – Translocation – Duplication

Mutations • Deletion: The loss of a piece of a chromosome due to breakage. • Inversion: a chromosomal segment breaks off flips around backwards and reattaches.

Mutations • Translocation: A piece of a chromosome breaks off and reattaches to a non homologous chromosome. • Duplication: A certain section of the chromosome gets copied twice.

Mutations • Another mutation that can occur is when sister chromatids fail to separate correctly during meiosis. • This is called Nondisjunction.

Chromosome Map • Scientists are able to locate individual genes on a chromosome. • Due to chromosome mapping scientists are able to tell if certain genes are damaged and the resulting disorder.

Pedigrees • Some Mutations are inherited. • Scientists can use Pedigrees to show a trait is inherited over generations.