Essay About Arrangement Of Chromosomes And Chromosome Complement Of A Cell

Human Genetic Disorders
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Genes
Definition
Segments of DNA molecules
A nucleotide sequence
Functions
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.
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
Types of Human Genetic disorders
Human Chromosomal Abnormalities
Nondisjunction
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
Down’s syndrome- trisomy 21
Edward’s syndrome- trisomy 18
Patau syndrome- trisomy 13
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
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
Sterile
Abnormally short an have webbed necks
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
Jacob syndrome or Double Y syndrome, XYY
Occurs in 1 in 1000 male births
First observed in 1960’s
Extra Y-chromosome predisposes the male to violent behavior
Hermaphrodites
Have both ovarian and testicular tissues
Do not have the normal Y; rather they have the minute y
Mental retardation, congenital anomalies and hypertonia
Chromosomal deletions
Abnormalities in chromosome structure due to some deletions in segments of some autosomal and sex chromosomes
cri-du-chat syndrome or 5 p sydrome
Deletion of the short arm of chromosome 5
Mentally retarded
With small epiglottis and larynx
Muscular dystrophy
Deletion of a small segment of chromosome X
Involves deletion of genes responsible for synthesis of the protein dystrophin.
Human Allelic Disorders (Recessive)
Albinism
not an infectious