Download Homework 2a Set A

1 Homeworkset2:HumanCytogenetics
Many human hereditary defects caused by chromosomal abnormalities may be identified by examining human chromosomes from cells that have been arrested in metaphase of mitosis — a stage when chromosomes are very short and compact. Leukocytes (white blood cells) or fetal cells obtained by amniocentesis or chorionic villus sampling are often used for diagnosis. The cells are cultured (to increase their number), treated with a chemical that disrupts the mitotic spindle apparatus, and placed in a hypotonic salt solution to swell their nuclei. The mixture is then centrifuged (to increase the concentration of cells) and transferred to a glass slide. As a drop of cell suspension hits the slide, the nuclei break open and the chromosomes spread apart; usually chromosomes from a single cell remain in an identifiable group. The cells are then stained, sometimes using special procedures that result in banded chromosomes (Figure 1). Figure 1. G‐banded chromosomes. This pattern is produced by using Giemsa stain. Bands do not represent genes, but do serve as markers for locating genes and gene families. The "metaphase spread" produced by a single cell is then photographed. The photograph can be cut apart and homologous chromosomes can be arranged in pairs according to size, location of the centromeres, and length of the chromosome arms. Chromosome pairs are arranged in a specific order and labeled. The result is called a karyotype. Match and order pairs of human chromosomes to make a karyotype. 1. Figure 2, is a sample karyotype that might assist you in matching chromosome pairs by size and banding. Figure 3 is a diagrammatic representation of G‐banded human chromosomes. (Note: This is NOT a karyotype, a karyotype would have 2 sets of each chromosome as humans cells are diploid) Figure 4 is a chromosome spread of banded chromosomes. Cut out these chromosomes and match them to the chromosomes shown in Figure 3. Match homologous chromosomes by size, length of arms, and the location of the centromere. Place the homologous pairs of Figure together above corresponding numbers in Figure 5. 2 2. O
Once you hav
ve matched the chromosomes, glue them onto the blank kaaryotype sheeets (Figures 7
7 to 9).
Figure 2. Karyotype o
of G‐banded
d human chromosomes
3 Figure 3. Normal Human Karyotype 4 Figure 4. Chromosome spread A 5 Set A DO NOT COMPLETE! Instead use the assembled karyotype on the last page. _ _ _ _ _ _ _ _ _ _ _ 1 2 3 4 5 6 _ 7 _ _ _ _ _ _ _ _ _ _ 8 9 10 11 12 _ _ _ _ _ _ _ _ _ _ _ 13 14 15 16 17 18 _ _ _ _ _ _ _ _ _ _ _ 19 20 21 22 X Y _ _ _ _ Figure 5. Match homologous chromosome pairs from Figure 4 and attach them in appropriate spaces above. Use the karyotype and the diagram (Figures 2 and 3) to help you match the pairs by size and banding patterns. Analysis: Analyze karyotype Set A to determine if a chromosomal abnormality exists. a) Will the child have a genetic disorder? b) Explain the reason for your answer. c) Use Table 1 to determine which genetic complication will affect the child. 6 Table 1: Genetic Disorders Genetic Disorder Down Syndrome Description of Disorder Chromosome Affected Extra Chromosome 21 47 chromosomes, mild to severe Trisomy 21 developmental abilities, almond ‐ shaped eyes, large tongue, prone to heart defects and respiratory problems. Turner Syndrome Single X in female (XO) Klinefelter Syndrome Extra X in Male (XXY) Jacobs Syndrome Triple X Syndrome 45 chromosomes, female lacking an X chromosome, normal in childhood, normal intelligence, fails to develop secondary sex characteristics and remains infertile. 47 chromosomes, male with an additional X chromosome, usually normal in appearance, normal intelligence, tall, underdeveloped testes, sterile, may also cause female characteristics (breast development, feminine body shape). Extra Y in Male (XYY) 47 chromosomes, male with an additional Y chromosome, low mental ability, normal in appearance. Extra X in Female (XXX) 47 chromosomes, male with an additional Y chromosome, low mental ability, normal in appearance. Edwards Syndrome Extra Chromome 18 Trisomy 18 47 chromosomes, mild to severe developmental problems: kidney malformations, heart defects, intestinal malformations, developmental delays, growth defeciencies, muscel disorders Patau Syndrome Extra Chromosome 13 Trisomy 13 47 chromosomes,severe developmental complications. Fetuses generally do not survive to birth. Abnormalities include defects in nervous system, muscles, genitalia, kidneys, and heart.