Chromosomal Karyotypes

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

Features of XYY Syndrome

Taller Comparatively low weight relative to stature Larger craniofacial dimensions Severe acne in adolescence Behavior problems – (prisoners) Learning disabilities Slightly lower IQ than normal High testosterone levels