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 X Y

Obtaining a Sample Fetal samples for karyotypes are commonly obtained in two ways 1. Amniocentesis – sample taken from the fluid of the amniotic sac 2. 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…

Overview I. Chromosomal Variations A. Polyploidy B. Aneuploidy II. Syndromes resulting from Aneuploidy A. Trisomy 13 B. Trisomy 18 C. Down Syndrome D. Turner Syndrome E. Klinefelter Syndrome F. 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 chromosomes 23 x 3 = 69 Tetraploidy – four sets of chromosomes 23 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 Trisomy Down Syndrome 3. Turner Syndrome 4. Klinefelter Syndrome 5. 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

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 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 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