Chapter 9: Genetic Engineering Section 9-1: Breeding New Organisms

The Appaloosa Horse The result of 200 years of selective breeding – choosing to mate individuals with desired characteristics Very strong, good temperament

Selective Breeding Concept behind pure bred cats and dogs, also used for crop plants Individual organisms with desired characteristics are chosen to produce the next generation.

Hybridization Selective breeding of dissimilar individuals (different characteristics) Way to combine the best characteristics of two organisms – Ex.: plant with disease resistance crossed with plant that produces a lot of food

Inbreeding Selective breeding of similar individuals (similar characteristics) Way to maintain breed once it is established – ensures preservation of the traits that make that breed unique Problems arise because members of the same breed are so genetically similar, the chances of recessive alleles pairing in increased, leading to genetic defects

Mutations A mutation is an inheritable change in genetic information Error in DNA replication Two types: – Chromosomal mutations – Gene mutations

Chromosomal Mutations Change in the number or structure of a cell’s chromosomes Chromosome number mutations occurs in meiosis when an entire set of chromosomes fails to separate (different from nondisjunction!!) Leads to polyploidy – three or more sets of chromosomes (fatal in animals, healthy in plants)

Chromosomal Mutations Chromosome structure mutations include: – Deletion - whole gene is deleted (Prader-Willi) – Duplication - one gene on a chromosome is duplicated – Inversion - pieces of the same chromosome invert (switch) – Translocation – piece of one chromosome breaks off and is reattached to another chromosome

Gene Mutations Affect only a single gene May involve one or more nucleotides Can have dramatic consequences Two main types: – Point mutations – Frameshift mutations

Point Mutations Involve a single nucleotide – A substitution occurs when one nucleotide is substituted for another nucleotide, causing a change in one of the amino acids in the sequence

Frameshift Mutations Involve the insertion or deletion of a nucleotide Cause a shift in the “reading frame,” altering the whole sequence past the point of mutation The fat cat ate the rat Deletion Tef atc ata ter her at Insertion Thh efa tca tat eth era t

Mutations and Breeding Most mutations are harmful, some can be desirable Sometimes, breeders attempt to increase the rate of mutations by exposing organisms to mutagens (mutation-causing agents) like X- rays, UV light, certain chemicals