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