Human Genetic Disorders
I. Genes
a. Definition
Segments of DNA molecules
A nucleotide sequence
b. 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.
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
1. 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
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
Sterile
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
a. Definition
Segments of DNA molecules
A nucleotide sequence
b. 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.
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
1. 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
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
Sterile
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