What is DNA?  Hershey and Chase—scientists that discovered DNA  Blueprint of living organisms  Can produce a variety of species with a common body plan  A complex polymer  Stands for deoxyribonucleic acid

DNA location  DNA is found in every cell, in every nucleus of every cell, and makes up each CHROMOSOME  Remember: Humans have 46 chromosomes, 23 pair, that code for all traits

DNA structure:  DNA structure is called a double-helix (looks like a twisted ladder) Formed by 2 strands of nucleotides bonded together in the middle (Called the Watson and Crick model)

DNA components:  DNA is made up of NUCLEOTIDES linked together  1 nucleotide = 1 phosphate, 1 sugar and 1 nitrogen base  The SIDES of DNA are made up of phosphates and sugars alternating  (P-S-P-S-P-S)

DNA Components:  The steps/rungs of the ladder structure are made up of pairs of nitrogen bases  The four nitrogen bases are:  Adenine, Thymine, Cytosine, Guanine *The bases always pair as follows:  A –T and C—G

DNA Components:  Base pairs are held together in the middle by HYDROGEN BONDS- which are weak bonds  *hydrogen bonds break and reform when DNA replication occurs

DNA Nucleotides  The sequence of the nucleotides determines the traits of the organism it composes  All organisms are made of DNA with the same four bases (A, T, C, G)  The ORDER of the bases determines the characteristics of the organism

DNA Replication  Before a cell divides, Replication must occur  Otherwise, offspring would have half the DNA of their parent cells  Replication: DNA’s ability to make a copy of itself (identical to the original)  this happens in the nucleus of the cell

Steps of Replication:  1. The DNA double strand unzips and untwists (beginning at one end)  2. Free floating nitrogen bases (A, T, C and G) assemble themselves along each side of the unzipped strand according to base- pairing rules  3. An enzyme glues the new base pairs in place  4. Each strand re-twists and re-coils

RNA  RNA—ribonucleic acid  mRNA—messenger RNA—used in forming proteins Single-stranded Contains ribose not deoxyribose Replaced thymine w/URACIL (there are no T’s in RNA)

Genetic Mutations (DNA)  Mutation—any mistake or change in the DNA sequence  May be caused by errors in making proteins, or cell division or by external agents (carcinogens, etc.)  CODON: a 3-base unit of a DNA strand—each codon codes for a particular protein

Mutations-cont’d.  Some mutations affect reproductive cells or gene in an organism. If the altered sperm or egg is fertilized, the mutation would then be inherited by offspring  Some gene mutations have positive effects (plant variations)  Some mutations effect genes that control cell division (cancer)

Mutations that occur during translation  Poin t mutation—a change in a single base pair in DNA (would effect that one codon only, and therefore one protein)  Frameshift mutation—if a single base were lost or added (would effect all codons read from that point on)  Shifts all codons up or down a base  (more harmful than a point mutation)

Chromosomal Mutations:  Chromosomal mutations: structural changes in chromosomes, more common in plants  Homologous chromosomes do not pair correctly when one chromosome has extra or missing parts, so separation of the chromosomes does not occur normally  Gametes could have extra copies or lack genes

Causes of Mutations  Some causes are unknown  Some are environmental  Mutagens: any agent that can cause a change in DNA Ex: radiation, chemicals, even high temps

Mendel and Heredity  Mendel—Austrian monk that studied pea plants to understand inheritance of traits  He carefully cross-pollinated pea plants to determine certain characteristics being passed from parent plant to offspring  He was the first person to succeed in predicting how traits are passed from one generation to the next

 Heredity: the passing of characteristics from parents to offspring  Traits: characteristics that are inherited  Genetics: the branch of biology that studies heredity

 Hybrid: the offspring of parents that have different forms of a trait ex: (tall and short height)  *Mendel’s first experiments were called MONOHYBRID CROSSES because they tested for a single trait’s inheritance

 Mendel concluded each organism has 2 factors that control each of its traits  Genes: pieces of a chromosome (pieces of DNA) that code for each trait  Genes exist in alternative forms called ALLELES

Alleles/Genes/Traits  Alleleles: are located on different copies of a chromosome-one inherited from a female parent and one inherited from a male parent  The two forms of alleles: Dominant and Recessive

 Dominant: (T) the observed allele/trait  Recessive: (t) the “masked” allele/trait  Dominant traits are those we actually observe, since they “mask”/overpower the recessive trait  Homozygous: both alleles are the same (can be dominant or recessive-TT or tt)  Heterozygous: both alleles are different (one of each-Tt)

 Homozygous Dominant: TT-Tall  Homozygous Recessive: tt-short  Heterozygous:Tt-Tall  *The only time the recessive allele is expressed, is when the alleles are homozygous recessive

 Phenotype: the physical appearance of an organism-how it looks and behaves: (ex: tall, short, etc.)  Genotype: the allele combination of an organism-the actual letters (ex: Tt, TT, tt)

Punnett Squares  Punnett Square: A way of showing possible genotypes of offspring of two particular parents, for a certain trait  Monohybrid cross-tests outcome of only 1 trait T t T