CHROMOSOME STRUCTURE
page 12
• EUKARYOTIC – DNA wrapped around histone
proteins.
• Banding pattern – dark – heterochromatin –
non-coding
• Light – euchromatin – DNA
that codes for proteins
Prokaryotic chromosomes
• DNA wrapped around DNA binding proteins
forming a single circular chromosome
Eukaryotic chromosome
Map of chromosome #4
Chromosomes- sex determination
karyotype
• a way to show chromosomes in a cell
• Usually taken at the metaphase stage
• Arranged according to size, centromere
position and banding patterns
• Can detect unusual chromosome numbers,
sizes and banding patterns
fluorescence in situ
hybridization
A modification on karyotyping
Fish for cml – 9-22 translocation
Examples of diseases that are
diagnosed using FISH include:
• Prader-Willi syndrome, Angelman syndrome,
22q13 deletion syndrome, chronic
myelogenous leukemia, acute lymphoblastic
leukemia, Cri-du-chat, Velocardiofacial
syndrome, and Down syndrome.
Sky karyotyping
• Provides a color code to identify particular
chromosomes
The Cell Cycle
page 10
Mitosis
Meiosis
•
•
•
•
•
•
Occurs in sexually reproducing organisms
Produces haploid gametes from diploid cells
Occurs in two stages
Meiosis I – homologous pairs separate
Meiosis II – chromatids separate
Four haploid gametes are produced ( for
sperm cells / three polar bodies and one
ovum)
Stages of Meiosis
MUTATION
page 21
L. CHROMO SOMAL DISORDERS IN NUMBER
AND THEIR CONSEQUENCES
1.NONDISJUNCTION VS. MOSAICISM
VS. CHIMERA
• NONDISJUNCTION - FAILURE OF
HOMOLOGOUS CHROMOSOMES TO
SEPARATE IN MEIOSIS
MOSAICISM - RESULTS
WHEN HOMOLOGOUS
CHROMOSOMES FAIL
TO SEPARATE
IN MITOSIS. FROM ONE
FERTILIZED EGG
u
CHIMERA - RESULTS FROM THE
FUSION OF TWO CELL LINES - EITHER
FROM A DOUBLE FERTILIZATION OR
FROM THE FUSION OF TWO
ZYGOTES. THE GENOTYPE XX/XY IS
FORMED EITHER FROM THE EGG
BEING FERTILIZED BY AN X SPERM &
A Y SPERM, OR FROM THE
FERTILIZED EGG & FERTILIZED
POLAR BODY FUSING
2. PLOIDY
• AN EXTRA COMPLETE SET OF
CHROMOSOMES; 3N- TRIPLOID; 4N TETRAPLOID; USUALLY LETHAL, BUT MAY
OCCUR IN HUMAN LIVER CELLS
• Induced in plants (using colchicine) to produce
Seedless varieties
3. SOMY
• INVOLVES NONDISJUNCTION IN A PAIR OF
CHROMOSOMES, EX. MONOSOMY & TRISOMY
a. AUTOSOMAL TRISOMIES
• TRISOMY 21 - DOWN’S SYNDROME, occurs in all
population subgroups and in chimpanzees
• TRISOMY 18 - EDWARD’S SYNDROME few survive,
then only a few weeks, occurs 4:1 in females:males
• TRISOMY 13 - PATAU’S SYNDROME most die before
the age of three months
b. GONOSOMAL
ABNORMALITIES IN
NUMBER
• Turner’s Syndrome - XO a.k.a. gonadal
dysgenesis
u
u
Klinefelter’s Syndrome - XXY, XXXY…
a.k.a. seminiferous tubule dysgenesis
Polysomal X - Triple 47 XXX, Tetra 48
XXXX, Penta 49 XXXXX… a.k.a. “Super
Female” tetra, penta - mental retardation
• XYY - due to a nondisjunction in male germ cell, or a
mitotic nondisjunction in zygote male tall with
severe acne, was once believed to be correlated
with criminal behavior, those advocating a eugenic
philosophy proposed testing for and isolating the
“genetic criminals” before they do society harm.
M. CHROMOSOME TYPES
• METACENTRIC
SUBMETACENTRIC
ACROCENTRIC
CHROMOSOME TYPES (CONT.)
• TERMINOLOGY OF THE ARMS
p - short arm
q - long arm
N. CHROMOSOMAL
DISORDERS IN
STRUCTURE
u
1. INVERSIONS - USUALLY DO NOT
AFFECT THE GENOTYPE OF THE
ORGANISM, THEY DO HOWEVER
AFFECT LINKAGE GROUPS.
2. TRANSLOCATIONS
• A. RECIPROCAL - AN EXCHANGE
BETWEEN NON HOMOLOGOUS
CHROMOSOMES
• (1) ANEUCENTRIC- PRODUCES DICENTRIC
AND ACENTRIC CHROMOSOMES, ALMOST
NEVER SURVIVE THE NEXT DIVISION
• (2) EUCENTRIC - EACH RESULTING
CHROMOSOME HAS ONE CENTROMERE.
MOST COMMON TYPE OF TRANSLOCATION.
PHILADELPHIA CHROMOSOME
• FOUND IN PATIENTS WITH CHRONIC
GRANULOCYTIC LEUKEMIA - A
TRANSLOCATION BETWEEN 22 & 9. THE LONG
ARM PORTION OF 22 (22q) IS LOST AND THE
LONG ARM OF 9 (9q) GAINS.
ROBERTSONIAN TRANSLOCATION/
FUSION
• TRANSLOCATIONS OF UNEQUAL
INTERCHANGES BETWEEN ACROCENTRIC
CHROMOSOMES (14 & 21)
SAME GENETIC
MATERIAL,
BUT A DECREASE IN
# OF CHROMOSOMES
3. DELETIONS
• a) partial monosomy
ex. Wolf Hirschhorn Syndrome
»4p»deletion of the short arm of
chromosome #4
»defect of midline fusion
Cats Cry Syndrome - Cri-du-chat
•
•
•
•
•
5pmental and motor disorder
growth retardation
simian fold in the hands
microcephaly
Refractory Anemia Syndrome
• 5q• increased platelet count
Wilms Tumor
•
•
•
•
•
11paniridia
ambiguous genitalia
mental retardation
kidney malignancy
Retinoblastoma
• 13q• DELETION OF TUMOR
SUPPRESSOR GENE
RESULTS IN TUMORS
IN THE EYE