Human Genetic Disorders

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•Segments of DNA molecules
•A nucleotide sequence

•Control of hereditary traits
•Sequence coding for a polypeptide which maybe an enzyme, or a part of an enzyme, which in turn is responsible for a certain phenotype or trait. c.The Human Karyotype
•Ordered arrangement of chromosomes arranged in homologous pairs •The chromosome complement of a cell or organism characterized by the number, size and morphological features of each chromosome

II.Types of Human Genetic disorders
a.Human Chromosomal Abnormalities
•Occurs when homologous chromosomes fail to segregate during meiosis •Produces gametes with three chromosome pairs (trisomy) or only one chromosome of a normal pair (monosomy) •Involves any chromosomes, including the sex chromosomes

•Causes serious genetic disorders
Ex: Down's syndrome- trisomy 21
Edward's syndrome- trisomy 18
Patau syndrome- trisomy 13
2.Klinefelter's syndrome, XXY
•Results when an abnormal sperm, containing both X and Y-chromosomes, fertilizes a normal egg with one X-chromosome •Can also result when an XX egg is fertilized by a Y sperm •Offspring has genotype XXY

•Occurs in 1 in 1000 born males
•Have reduced fertility and maybe mentally retarded
3.Turner's syndrome, XO
•Results from the absence of an X-chromosome in an egg
•When fertilized by a normal X-carrying sperm, offspring has the genotype XO ("O" indicating the lack of a chromosome) •XO occur in 1 in 2000 born females
•They do not mature sexually
•Abnormally short an have webbed necks
4.Triplo-X syndrome, XXX
•Occurs at the frequency of 1 in 1000 live female births
•Do not have distinct clinical features except for tallness and menstrual irregularities, secondary amenorrhea and premature menopause •Mostly have no sexual abnormalities but are generally of subnormal mental abilities 5.Jacob syndrome or Double Y syndrome, XYY

•Occurs in 1 in 1000 male births...
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