Genetic Disorders PDF

GENETIC DISORDERS A change in the number or structure of chromosomes can dramatically change the traits of an organism and can cause serious problems. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or...

GENETIC DISORDERS A change in the number or structure of chromosomes can dramatically change the traits of an organism and can cause serious problems. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or more of these: Errors during dividing of sex cells (meiosis) Errors during dividing of other cells (mitosis) Exposure to substances that can cause birth defects (teratogens) Figure 2: Normal human karyotype. Male karyotype (left) and female karyotype (right).  Karyotyping is the process by which photographs of chromosomes are taken in order to determine the chromosome complement of an individual, including the number of chromosomes and any abnormalities. Numerical abnormality also called aneuploidy, a condition which occurs when an individual has a missing chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.). Examples of chromosomal abnormalities under this category include the following: Down Syndrome (Trisomy 21) ✓ The most common disorder of trisomy is Down syndrome, wherein the 21st chromosome has three instead of two chromosomes. ✓ Most cases of Down syndrome are not due to inheritance but on random mistakes during formation of reproductive cells of the parents. ✓ Physical manifestations: Short neck, with excess skin at back of the neck. Flattened Figure 3: Child with facial profile and nose. Small head, ears, and Down Syndrome (file retrieved from Google marked mouth. Upward slanting eyes. as “labeled for reuse”) Turner Syndrome (45, XO) ✓ A condition that affects only female as a result of one of the X chromosomes (sex chromosome) is missing or partially missing. ✓ Physical manifestations: Webbed neck, short stature, swollen hands and feet. Some have skeletal abnormalities, kidney problems, and/or congenital heart defect. Klinefelter Syndrome (47, XXY) ✓ A condition resulting from two or more X chromosomes in males ✓ Manifestations are typically more severe if three or more X chromosomes are present as Figure 4: Turner in (48, XXXY) or (49, XXXXY). Syndrome (file retrieved from Google marked as Physical manifestations: Primary features are “labeled for reuse” infertility and small poorly functioning testicles. Sometimes includes weaker muscle, greater height, poor coordination, less body hair, breast growth and less interest in sex. Figure 5: Klinefelter from Google marked as “labeled for reuse”) Trisomy X Syndrome (47, XXX) ✓ Characterized by the presence of extra X chromosome in each cell of a female ✓ Physical manifestations: Often taller than normal, affected individuals have usually mild symptoms to none at all. Occasionally there are learning difficulties, delayed speech, decreased muscle tone, seizures, retrieved from Google or kidney problems. marked as “labeled for reuse”) Patau Syndrome (Trisomy 13) ✓ Caused by having an additional copy of chromosome 13 in some or all of the body’s cells. ✓ Physical manifestations: Clenched hands, cleft lip or palate, extra fingers or toes (polydactyly), hernias, kidney, wrist or Figure 7: Patau Syndrome (file retrieved from Google scalp problems, low-set ears, small head, marked as “labeled for undescended testis. reuse”) Edward Syndrome (Trisomy 18) ✓ Caused by having additional copy of chromosome 18 ✓ Physical manifestations: Cleft palate, Clenched fists, defects of lungs, kidneys and stomach, deformed feet, heart defects, low-set ears, (file retrieved from Google severe developmental delays, chest marked as “labeled for deformity, slowed growth, small head, small reuse”) jaw. Structural abnormalities occur when the chromosome’s structure is altered, which can take several forms such as: Deletion – a portion of a chromosome is missing or deleted; Duplication – segment of a chromosome is repeated twice; Translocation – transfer of a section of one chromosome to non-homologous chromosome; Inversion – a section of the chromosome becomes changed by rotation at 180 degrees Cri-du-chat Syndrome (5p minus syndrome) ✓ A genetic condition caused by the deletion of genetic material on the small arm (p arm) of chromosome 5 ✓ Physical manifestations: mentally retarded, has abnormal development of glottis and larynx resulting from a crying sounds that sound like the meowing of a cat. chat Syndrome (file retrieved from Google marked as “labeled for reuse”)