Chromosomes and Karyotypes

Chromosome Structure Metaphase Chromosome Histone Proteins Double Chromosomes are complex structures containing DNA and proteins known as histones. DNA is wound around the histones and these in turn are coiled into larger loops and so on and so forth. This compacting allows DNA to occupy less space and to be reliably divided up during cell division. Metaphase Chromosome Histone Proteins Double Helix

Chromosome Structure Metaphase Human Chromosomes Sex chromosomes Human Sex Chromosomes, Biology, McDougal Littell, 2008. Condensed chromosomes at metaphase. The DNA is tightly coiled and becomes visible under the light microscope. http://www.pinterest.com/pin/253538653997202347/ Scanning electron micrograph of chromosomes in mid telophase http://classes.biology.ucsd.edu/bimm110.SP07/lectures_WEB/L08.05_Cytogenetics.htm Human chromosome set before sorting Metaphase Human Chromosomes

How Karyotypes are Created - I

How Karyotypes are Created - II Well-stained metaphase spreads are photographed Each of chromosome images is cut out of the picture Matched with its partner Arranged from largest to smallest on a chart The largest autosome is number 1

How Karyotypes are Organized Classification of solid-stained chromosomes Metacentric chromosomes: centromere in the middle. Acrocentric chromosomes: centromere close to one end; this gives very short p-arm.

Normal Human Karyotype

Normal Female Karyotype

Normal Male Karyotype

Patau Syndrome. trisomy 13 (47, XX, +13). It is rare for fetuses to go to term; less than 5% reach 3 years. Cleft lip and palate, broad nose, small cranium, polydactyl, deafness, and nonfunctional eyes, heart defects and severe mental retardation.

Down syndrome – Trisomy 21 - 1/6 die within the first year and the average life span is 16.2 years. mental retardation - IQ between 25-74. Short stature, broad hands, stubby fingers and toes, a wide rounded face, a large protruding tongue that makes speech difficult. Individuals with this syndrome have a high incidence of respiratory infections, heart defects, and leukemia.

Klinefelter's syndrome with a 47, XXY karyotype. This particular anomaly is relatively common (about 1 in 500 males), Characteristics associated with this condition are tall stature and sterility.

Jacobs Syndrome - 47 XYY karyotype. Occurence is 1/1000 live male births. Men with this karyotype are tall and have lower mental ability.

Turner's syndrome, with karyotype 45, X. unable to bear children. short stature, short broad neck, and a broad chest. Intelligence does not seem to be affected.

Cri-du-chat. - one chromosome #5 upper arm deletion Babies cry sounds like that of a cat in distress: severely mentally retarded, round face, low set ears, heart disease, and have a small cranium.

Edwards Syndrome. trisomy 18 (47, XY, +18) Edwards Syndrome. trisomy 18 (47, XY, +18). It is uncommon for fetuses with this condition to survive, 1 in 8000 live births. 10% survive one year highly characteristic pattern of malformations: elongated skull, a very narrow pelvis, rocker bottom feet and a grasping of the two central fingers by the thumb and little finger, ears are often low set and the mouth and teeth are small.

Practice Karyotyping

Genetic Testing for Chromosomal Abnormalities Abnormality Name Trisomy 21 Downs Syndrome Trisomy 18 Edwards syndrome Trisomy 13 X, XXX, XYY, XXY 22q11.2 deletion DiGeorgi syndrome 5p minus Cri-du-chat syndrome 1p36 deletion Prader-Willims yndrome 1p36 deletion syndrome Trisomy 16 Trisomy 22 At the present time, genetic testing is available for the following genetic abnormalities. All offer significant challenges to prospective parents. We are generally familiar with Downs syndrome. Edwards syndrome is rare ( 1 in 5000 live births) and presents medical complications that are life threatening. Chromosomal deletions are also very serious. DiGeorgi syndrome is also rare (1 in 4000 births) and is often associated with congenital heart failure and learning disabilities. Cri du chat we discussed earlier. Prader-Willi syndrome (1 in 10,000 births) presents as low muscle tone, short stature and life threatening obesity.