Chromosome Number and
Structure
Genetics
36404
1
Announcement
• Exam 2 - Wednesday, Oct. 2
• Epistasis, Polygenic, Linkage,
Chromosome Abnormalities
a+
Test Cross
a
a
a+r+ x a r
ar
ar
r+ r
wild
x
a
r r
no wings, curved
a+r+
a + r+
ar
a+r+
ar
ar
wild
Total = 242
Recombinant = 45
105
ar
ar
ar
a+r
a r+
a+r
a r+
ar
ar
no wings curved
curved
102
23
% Recombinant = 45/242 * 100 = 18.6%
a
ar
ar
no wings
22
18.6
r
Linkage Mapping
• white - miniature 34.5%
• white - yellow 0.5%
• yellow - miniature 35.4%
0.5
34.5
y w
m
35.4
Drosophila
Chromosome
Map
See textbook
Figure 5-13
Karyotype
• Photograph of chromosomes
See handout
Basic Chromosome Structure
non-replicated
chromosome
replicated
chromosome
p arm
centromere
q arm
chromatids
Chromosome Shape
Metacentric
Acrocentric
Submetacentric
Telocentric
Satellites
Karyotype Analysis
Groups
A large metacentric
B large submetacentric
C medium submetacentric
D medium acrocentric
E small submetacentric
F small metacentric
G small acrocentric
X meduim submetacentric
Y small acrocentric
9
Karyotype Analysis
Autosomes - 1st 22 pairs of chromosomes
Sex Chromosomes - 23rd pair, XX or Xy
46XX female
46XY male
10
Aneuploidy
• Gain or lose of 1 or more chromosomes
but not a whole set
• Monosomy - missing 1 chromosome
• Trisomy - extra chromosome
11
Klinefelter’s Syndrome
•
•
•
•
•
47XXY
tall
sm. breast
sm. testes
poor beard
Turner’s Syndrome
•
•
•
•
45X
short
webbed neck
shield chest
Jacob’s Syndrome
• 47 XYY
• decreased
intelligence
• tall
Superfemale
• 47 XXX
• no specific
abnormalities
Down’s Syndrome
• 47 XX or XY + 21
•
•
•
•
mental retardation
round head
broad hands
short fingers
Edward’s Syndrome
•
•
•
•
47 XX or XY + 18
retarded
long skull
low ears
Patau’s Syndrome
• 47 XX or XY + 13
• cleft lip
• small head
Chromosome Abnormalities/
100,000 Pregnancies
Abnormality
Spont. Aborts
Live Births
normal
7500
84450
trisomy 13
128
17
trisomy 18
223
13
trisomy 21
350
113
other autosomes trisomy
3176
0
47 xyy
4
46
47 xxy
4
44
45 x
1350
8
47 xxx
21
44
translocation
239
216
polyploids
1725
0
other
280
49
Y-Chromosome
SrY
•
•
•
•
•
•
•
SRY Gene
Codes for Testes Determining Factor
stimulates testes dev.
testes->testosterone
testosterone->male characterisitics
XY or XXY or XYY male
XY female if SRY missing
X-Chromosome
dystrophin
•
•
•
•
color vision
hemophilia
contains many genes
only one active in any cell
random as to which one
inactive forms a Barr Body
Barr Bodies
•
•
•
•
•
•
•
Inactive X Chromosomes
Only 1 active X chromosome in a cell
Female XX - one Barr Body
Male XY - no Barr Body
Klinefelter’s male XXY - one Barr body
Turner’s female X - no Barr body
Superfemale XXX - 2 Barr bodies
22
Heterozygote on X
•
•
•
•
•
A=produces sweat gland
a=no sweat gland
AA or Ay normal
aa or ay no sweat glands
Aa mosaic - patches of
sweat glands and areas of
no sweat glands
23
Calico Cat - Heterozygote on X
• Always female
• Heterozygote for color on X
• Some patches have X with
normal color gene
• Other patches have X with
defective color gene
G1
G2
End of 1st Division
2N=4
Normal
Meiosis
End of 2nd Division
G1
G2
Nondisjunction
1st Division
Gametes with
extra
chromosome
Gametes with missing chromosome
G1
Nondisjunction
2nd division
Gamete with missing
chromosome
G2
normal
gametes
Gamete with extra
chromosome
Fertilization with Normal Sperm
Gamete with missing
chromosome
Gamete with extra
chromosome
28
Monosomy
Trisomy
Curse of Garcias
• Read article
• Answer questions