Download 12-4 Notes

12-4 Notes
Mutations
Kinds of mutations
 Cells can make mistakes in copying their
own DNA, as the new strand is put
together.
 These mistakes are called mutations.
 Mutations come in many shapes and sizes.
Kinds of mutations
Two main types:
1.) Gene mutations are changes in a
single gene.
2.) Chromosomal mutations cause
changes in whole chromosomes.
Gene Mutations
 Gene mutations that occur at a single
point in the DNA sequence are called point
mutations.
 When a point mutation causes one base to
replace another, only one amino acid is
affected.
 EX: substitution
Gene Mutations
 If a nucleotide is added or taken away,
it causes a frame shift mutation.
 All the groupings of codons are
changed because they are read in
groups of three.
 This can cause the gene to produce a
completely different protein.
 It can be altered so much that it is
unable to perform its normal functions.
 EX: insertion or deletion
Chromosomal Mutations
 Chromosomal mutations involve changes in
the number or structure of chromosomes.
 4 types:
 1. deletions-loss of all or part of a chromosome
 2. duplication-produce extra copies
 3. inversion-reverse the direction
 4. translocation-breaks off and attaches to
another
Significance of Mutations
 Many mutations have little or no effect on
genes or the functions of proteins.
 Plant and animal breeders take advantage
of such beneficial mutations.
 Polyploid plants have an extra set of
chromosomes that are larger and
stronger.
 Bananas and many citrus fruits are
produced this way.
Significance of Mutations
 Harmful mutations produce defective
proteins that disrupt normal biological
activities.
 They are the cause of many genetic
disorders and are associated with many
types of cancer.
12-5 Notes
Gene Regulation
Gene Regulation
 Certain DNA sequences serve as binding
sites for RNA polymerase, called
promoters.
 Others serve as start and stop signals for
transcription.
 There are “regulator sites” where proteins
can regulate transcription.
 These proteins help determine whether a
gene is turned on or off.
Prokaryotes
• Two regulatory proteins control when genes are
turned on or off:
 1.) Promoter- RNA polymerase binds and
begins transcription.
 When this protein is no longer needed it makes a
repressor.
 2.) Operator- The repressor binds here when
the operon is “off”.
 The repressor prevents RNA polymerase from
beginning the process of transcription.
Eukaryotes
 The regulation of eukaryotic cells are
controlled individually and very complex.
 There is a “TATA box” that helps position
RNA polymerase for transcription.
Development & Differentiation
 Regulating gene expression helps to shape
the way an organism develops.
 The different cell types found in an adult
develop from the same fertilized egg.
 Cells grow, divide, and become specialized
in structure and function, called
differentiation.
 Hox genes control differentiation of cells
and tissues in the embryo.
13-1 Notes
Changing the Living World
Selective Breeding
 For years people have bred dogs to get
desired traits.
 EX: better hunters, companions, height, hair or
nose type
 To obtain these desired characteristics
people have used selective breeding.
 Now these desired traits are passed on to
the next generation.
Hybridization
 American Luther Burbank developed more
than 800 varieties of plants including the
disease-resistant Burbank potato.
 Burbank used a process called
hybridization.
 This process crosses dissimilar individuals
and brings out their best traits.
 The hybrids that are produced are hardier
than either of the parents.
Inbreeding
 Inbreeding is required to maintain the
characteristics of pedigreed dogs.
 It helps to ensure each breeds unique
characteristics will be preserved.
 However, inbreeding has increased the
breed’s susceptibility to diseases and
deformities.
Increased Variation
 Genetic variation can be increased in a
population by inducing mutations.
 This can be done by using radiation and
chemicals which is harmful to the
organism.
 If breeders are patient they can produce
mutants with the desired characteristics.
Inducing Mutations in Bacteria and
Plants
 Using this technique, scientists have been
able to develop hundreds of useful
bacterial strains.
 EX: Bacteria that can digest oil spills.
 Drugs are used to produce cells that have
double or triple the normal number of
chromosomes (polyploidy).
 Polyploidy produces new species of plants
that are larger and stronger than their
diploid relatives.
 EX: Day lilies and citrus fruits