Chapter 15: Human Genetics Karyotypes, Down Syndrome, sex chromosomes, abnormalities, autosomal...
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Transcript of Chapter 15: Human Genetics Karyotypes, Down Syndrome, sex chromosomes, abnormalities, autosomal...
Chapter 15: Human Genetics
• Karyotypes, Down Syndrome, sex chromosomes, abnormalities, autosomal genes, sex-linked genes, and polygenic inheritance are covered in this Chapter.
Inheritance 0f Chromosomes
• Somatic cells - 22 pairs of autosomes, 1 pair sex chromo
• Karyotype - shows chromo’s paired by size, shape, & appearance in metaphase
• members in a pair have same banding patterns
Inheritance 0f Chromosomes
• Nondisjunction - occurs during meiosis, causing abnormal chromo #
• Nondisjunction is the failure of one or more chromo’s to separate during MI or when daughter chromo’s fail to separate during MII.
Inheritance 0f Chromosomes
• Down Syndrome - common autosomal trisomy
• 3 copies of chromo 21
• 23% cases sperm had extra chromo 21
• chance of woman having down syndrome child increases w/ age.
Abnormal Sex Chromosomal Inheritance
• Turner (XO) syndrome - females have only one X chromo
• Females are short, broad chest, folds of skin on neck
• Ovaries never functional, never undergo puberty
Abnormal Sex Chromosomal Inheritance
• Klinefelter syndrome - males have one Y and 2 X chromos
• individuals have large hands and feet and long arms and legs.
Abnnormal Sex Chromosomal Inheritance
• Triplo-X females
• Jacob syndrome (XYY)
• Males w/Jacob’s syndrome are taller than average, have persistent acne, tend to have lower intelligence
Abnormal Sex Chromosomal Inheritance
• Fragile X Syndrome - X chromo nearly broken, most often found in males
• hyperactive or autistic children, delayed speech
• Traced to excessive copies of CGG triplet
Autosomal Genetic Disorders
• Males=squares, females=circles
• Carrier- Has no apparent abnormality but can pass on allele for recessively inherited genetic disorder
Autosomal Dominant Disorders
• Neurofibromatosis - have tan skin spots at birth that turn to benign tumors
• 1 in 3,000 people effected
• Neurofibromas are lumps under the skin of nerves and other cells
Autosomal Dominant Disorders
• Huntington Disease effects 1 in 20,000
• leads to degeneration of brain cells
• Death in 10-15 years from onset
• Gene for disease on chromo 4; contains repeats of CAG
Autosomal Recessive Disorders
• Cystic Fibrosis - most common lethal genetic disease in Caucasions
• 1 in 20 is a carrier, 1 in 2,500 has disorder
• Production of mucus in lungs and pancreas
• Gene on Chromo 7
Autosomal Recessive Disorders
• Tay-Sachs Disease - in Jewish people
• Symptoms not apparent, child becomes blind & helpless, develops seizures.
• Death by 3-y yrs.
• Lack of enzyme hexosaminidase
Autosomal Recessive Disorders
• Phenylketonuria(PKU)• 1 in 5,000 births• Lack of enzyme needed
to metabolize aa phenyalanine
• Mutated gene on chromo 12
• Child placed on low phenyalanine diet till age 7.
Beyond Simple Mendelian Inheritance
• Polygenic Inheritance - 1 trait governed by 2 or more sets of alleles
• Includes diabetes, schizophrenia, allergies, and cancers
Beyond Simple Mendelian Inheritance
• Sickle-cell disease controlled by incomplete dominant alleles
• Blood cells irregularly shaped (abnormal hemoglobin), clog vessels and break down
• poor circulation, anemia, low resistnce to infection, jaundice...
Sex-linked Genetic Disorders
• Traits controlled on sex chromo are sex-linked
• Y-chromo smaller, most sex linked are on the X-chromo
• Males get X-linked traits from mom
• Daughter must have a carrier mom and an expressed dad.
Sex-linked Genetic Disorders• Color Blindness -
recessive disorder involving mutations of genes coding for green or red sensitive cone cells
• Cannot see red or green respectively
Sex-linked Genetic Disorders
• Muscular Dystrophy - characterized by wasting away of muscles, eventually leading to death
• 1 in 3,600 births• fails to produce protein
dystrophin• waddling gait, toe walking,
frequent falls, difficulty rising.
• Death by 20 yrs old
Sex-linked Genetic Disorders• Hemophilia - impaired
ability to clot• 1 in 10,000 males• Hemophiliacs bleed
externally after an injury and also suffer internal bleeding around joints
• Need blood transfusions or conc. of clotting protein