Download Unit III: DNA and Inheritance

Unit III: DNA and Inheritance
Gene Mutations
Tortoiseshell Cat--gene expression
--only females (X-linked)
“Stormy”
Fig. 25.2
Gene Mutations
--any change in gene sequence-HOW DO THEY HAPPEN??
Errors in Replication: rare; DNA Polymerase
“proofreads” and corrects mistakes
Mutagens: low rate; environmental influences (UV
radiation, certain chemicals); DNA repair
enzymes fix damage
Transposons: “jumping genes”; specific sequences of DNA
that can change locations on chromosomes
Transposons
Indian Corn
FIG. 24.16
Types of Mutations
•FRAMESHIFT--insertion or deletion of a
nucleotide; changes how the
triplet code is read;
•THE CAT ATE THE RAT
•THE ATA TET HER AT (“C” REMOVED)
•POINT MUTATION--substitution of one nucleotide
for another
silent--codes for same amino acid
nonsense--codes for “stop”
missense--changes amino acid and shape
Sickle Cell Anemia
•Point Mutation
(single nucleotide)
•Changes shape of
hemoglobin (HB)
•HB forms stiff rods
•Can’t carry O2
FIG. 26.13
Nondisjunction in Meiosis=change in chromosome #
3 chromosomes
Fig. 26.2
EXTRA CHROMOSOME--Trisomy 21
•Down Syndrome
•Nondisjunction
•Affects all cells
Fig. 26.1
Fig. 26.3.b1
TRISOMY 21-Gart gene
Gart gene
Abnormal Sex Chromosome Number
XO
XXY
Fig. 26.4
TURNER SYNDROME KLINEFELTER SYNDROME
Muscular Dystrophy--X-linked
FIG. 26
Fig. 26.5
Gene Deletion--Williams Syndrome
Fig. 26.6
Duplication and Inversion--”inv dup 15” syndrome
Fig. 26.7
Translocation--chromosomes 2 and 20
(Alagille Syndrome)
Two non-homologous chromosomes exchange segments
Fig. 26.8
Inversion (during Meiosis)