Chromosomes
Definition Genetic structures of cells containing
DNA
Identification Each chromosome has a characteristic
length and banding pattern
The breakdown of a Chromosome
Each autosome is numbered from 1-22, sex chromosomes either X or Y
p arm (short arm)
q arm (long arm)
Centromere
Chromosome Labeling
Example - 1q2.4 The first chromosome, long arm, second region
of the chromosome, the fourth band of that sub-region
Chromosome is identified with a number ranging 1-22, or X and Y
Each arm divided into sub-regions and identified by a number
Each sub-region divided into bands identified with a number
A Karyotype
Definition A photographic
arrangement of a complete set of chromosomes of a cell or organism
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 X Y
Obtaining a Sample
Fetal samples for karyotypes are commonly obtained in two ways1. Amniocentesis – sample taken from
the fluid of the amniotic sac2. Chorionic Villus Sampling – sample taken from fetal tissue that forms part
of the placenta
Obtaining a Karyotype
Chromosomes are stained for easy visualization
Light microscope used to view chromosomes in metaphase of mitosis
Chromosomes arranged into homologous pairs based on size and banding patterns
Staining
Banding patterns can be visually identified on chromosomes after staining.
Traditional Types G-Banding – Giemsa stain Q-Banding – Fluorescent stain R-Banding – Reverse Giemsa stain
New Type Fluorescence In Situ Hybridization techniques
Importance of Karyotypes
Karyotypes show the chromosomal makeup of an individual.
Knowing the number of chromosomes is essential for identifying chromosomal variations that cause genetic disorders…
OverviewI. Chromosomal Variations
A. PolyploidyB. Aneuploidy
II. Syndromes resulting from AneuploidyA. Trisomy 13B. Trisomy 18C. Down SyndromeD. Turner SyndromeE. Klinefelter SyndromeF. XYY Syndrome
Variations in Chromosomal Number
Euploidy – the normal number and sets of chromosomes
Polyploidy – the presence of three or more complete sets of chromosomes
Aneuploidy – the presence of additional or missing individual chromosomes
Types of Polyploidy
Triploidy – three sets of chromosomes23 x 3 = 69
Tetraploidy – four sets of chromosomes23 x 4 = 92
Types of Aneuploidy
Monosomy – one less chromosome(23 x 2) – 1 = 45
Trisomy – one additional chromosome(23 x 2) + 1 = 47
Aneuploidy in Humans
When aneuploidy occurs in humans, syndromes can result.
1. Trisomy 132. Trisomy 183. Down Syndrome3. Turner Syndrome4. Klinefelter Syndrome5. XYY Syndrome
Trisomy 13 (Patau Syndrome)
Chromosomal Variation – Trisomy 13(three copies of chromosome 13)
Occurrence – 1 in 5000
Features of Trisomy 13
Severe mental retardation Head and facial abnormalities Extra fingers and toes Kidney malformations Heart defects Early death < 1 year
Trisomy 18 (Edwards Syndrome)
Chromosomal Variation – Trisomy 18 (three copies of chromosome 18)
Occurrence – 1 in 8000
Syndactyly
Features of Trisomy 18
Severe mental retardation Head and facial malformations Malformations of the hands and feet Skeletal malformations Kidney malformations Structural heart defects Early death < 1 year
Trisomy 21 (Down Syndrome)
Chromosomal Variation – Trisomy 21 (three copies of chromosome 21)
Occurrence – 1 in 800-1000
Features of Down Syndrome
Low muscle tone Head and facial malformations Abnormalities of the extremities Mental retardation Heart malformations Increased risk of infectious disease Early death
Turner Syndrome
Monosomy of sex chromosome(only one X chromosome present)
Occurrence – 1 in 2500 live female births
Features of Turner Syndrome
Short stature Lack of ovarian development Neck abnormalities Skeletal disorders Increased risk of osteoporosis,
cardiovascular constriction, diabetes, and kidney and thyroid problems
Klinefelter Syndrome
Trisomy of sex chromosome - XXY(An additional X chromosome in males)
Occurrence – 1 in 500-1000 males
Features of Klinefelter Syndrome
Tall Sexually underdeveloped Infertility Sparse facial and body hair Developmental delays Increased risk of autoimmune disorders,
breast cancer, osteoporosis, leg ulcers, depression, and dental problems
XYY Syndrome
Trisomy of sex chromosome – XYY(An additional Y chromosome in males)
Occurrence – 1 in 1000-2000 men