chromosome structure page 12 eukaryotic – dna wrapped around histone proteins. banding pattern –...
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CHROMOSOME STRUCTUREpage 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
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
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.
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)
1.NONDISJUNCTION VS. MOSAICISM VS. CHIMERA
• NONDISJUNCTION - FAILURE OF HOMOLOGOUS CHROMOSOMES TO SEPARATE IN MEIOSIS
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
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 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.
N. CHROMOSOMAL DISORDERS IN
STRUCTURE 1. INVERSIONS - USUALLY DO NOT
AFFECT THE GENOTYPE OF THE ORGANISM, THEY DO HOWEVER AFFECT LINKAGE GROUPS.
• (1) ANEUCENTRIC- PRODUCES DICENTRIC AND ACENTRIC CHROMOSOMES, ALMOST NEVER SURVIVE THE NEXT DIVISION
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)
ex. Wolf Hirschhorn Syndrome
»4p-»deletion of the short arm of
chromosome #4»defect of midline fusion
Cats Cry Syndrome - Cri-du-chat
• 5p-• mental and motor disorder• growth retardation• simian fold in the hands• microcephaly