I. Chromosome Theory- Although Mendel worked out many of the basic facts of heredity, he did not know about chromosomes or genes (he called them Mendel factors). Mendel worked in the 1850's, approximately 50 years later biologists rediscovered his work and made the connection between chromosomes and the units of heredity hypothesized by Mendel. In 1902, the geneticist Walter Sutton presented his chromosome theory of heredity.

A. Located in nucleus
B. Heredity material located here- genes (on the chromosomes)

C. Homologous chromosomes- pairs of similar chromosomes

1. Autosomes- 22 pairs of homologous chromosomes

a. genes located at identical positions are called alleles

2. Sex chromosomes- 1 pair

a. XX - female
b. XY - male (the 'Y' chromosome is only a piece of a chromosome)
c. Sex determination of the offspring is determined by the father

II. Sex-linked traits

A. alleles for traits that are located on the sex chromosomes

1. Morgan- worked with drosophila (fruit flies)
2. Humans- hemophilia, color blindness [recessive traits] located on the X chromosome

a. carrier- female chromosome, has trait on one of the X chromosome; males can NOT be carriers- if they have it on their X chromosome then they show the trait
b. shows the disease- females need it on both XX chromosomes, males only on the X chromosomes

B. Gene Linkage- genes located on the same chromosomes are inherited together [examples: hair color, eye color]
C. Crossing Over- pieces of chromosomes are exchanged during synapsis (separating of the chromosomes) of meiosis
D. Multiple Gene Inheritance- when 2 or more independent genes affect the same characteristic- polygenic inheritance
E. Environment and Heredity

1. Genes carry all the information for the life of the organism
2. Environment determines how much of the heredity information will be expressed- Himalayan Rabbit

III. Comparison of Deoxyribose Nucleic Acid (DNA) & Ribose Nucleic Acid (RNA)

A. Structure- both nucleic acids are made of nucleotides

1. Nucleotide is made of a phosphate, sugar, & a nitrogenous base

a. Since there are 4 different nitrogenous bases each, there are 4 different nucleotides

B. DNA

1. is double stranded, also called DOUBLE HELIX
2. contains sugar called deoxyribose (one less Oxygen molecule than ribose)
3. nucleotides: adenine, guanine, cytosine, thymine
4. hydrogen bonds connect the complementary bases (rungs of ladder for model)

C. RNA

1. is single stranded
2. contains sugar called ribose
3. nucleotides: adenine, guanine, cytosine, uracil
4. can move in & out of the nucleus

D. Forms & Functions of RNA

1. Messenger RNA (m-RNA): copy of DNA carries the "message" from the nucleus to the cytoplasm & the site of protein synthesis
2. Transfer RNA (t-RNA): structure that transfer amino acids which are attached to its tail to m-RNA
3. Ribosomal RNA (r-RNA): 2 sub-units that combine with protein to form a complete ribosome; provides the site for protein synthesis

IV. Replication of DNA

A. hydrogen bonds break
B. free nucleotides are inserted

V. Protein Synthesis- is called TRANSLATION

A. Steps:

1. m-RNA (with copy of DNA gene) moves from the nucleus to a ribosome (r-RNA)
2. t-RNA with the appropriate anticodon attaches to an amino acid (a.a.) & carries it to the ribosome
3. the amino acid is released & joins the polypeptide chain (many a.a. joined by peptide bonds) which is attached to the ribosome
4. t-RNA is released to pick up another a.a., then ribosome moves to the next codon on the m-RNA awaiting the next t-RNA (with appropriate anticodon)

B. [note] Transcription occurs before translation

1. m-RNA moves from the cytoplasm into the nucleus
2. then m-RNA copies (or transcribes) a DNA segement
3. then m-RNA moves from the nucleus to the ribosome