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

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 Cyclepage 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

MUTATIONpage 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 SEPARATEIN MITOSIS. FROM ONE FERTILIZED EGG

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 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

q - long arm

p - short arm

N. CHROMOSOMAL DISORDERS IN

STRUCTURE 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

• 5p-• mental and motor disorder• growth retardation• simian fold in the hands• microcephaly

Refractory Anemia Syndrome

• 5q-• increased platelet count

Wilms Tumor

• 11p-• aniridia• ambiguous genitalia• mental retardation• kidney malignancy

Retinoblastoma

• 13q-• DELETION OF TUMOR SUPPRESSOR GENE RESULTS IN TUMORS IN THE EYE