Transcript Chapter 9 (and Section 8-4): Genetic Engineering

Chapter 9:
Genetic Engineering
Section 9-1:
Breeding New
Organisms
The Appaloosa Horse
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The result of 200
years of selective
breeding –
choosing to mate
individuals with
desired
characteristics
Very strong, good
temperament
Selective Breeding
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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
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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
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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
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A mutation is an inheritable change in
genetic information
Error in DNA replication
Two types:
– Chromosomal mutations
– Gene mutations
Chromosomal Mutations
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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
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Chromosome structure mutations include:
–
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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
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Affect only a single gene
May involve one or more nucleotides
Can have dramatic consequences
Two main types:
– Point mutations
– Frameshift mutations
Point Mutations
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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
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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
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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 Xrays, UV light, certain chemicals