Pedigrees, Karyotypes and Genetic Disorders Inheritance patterns Pedigrees, Karyotypes and Genetic Disorders

Inheritance Patterns As Mendel discovered with his pea plants, to understand inheritance you have to look beyond one single generation to see how the trait is passed on from one generation to the next

Inheritance Patterns To observe inheritance of a specific trait you can look at several generations together in one diagram like a family tree

Inheritance Patterns Pedigree: chart showing the inheritance of traits through several generations

Inheritance Patterns Rules for making a pedigree: males are designated with square symbols. females with round symbols If the circles or squares are shaded it means they have the trait being studied Half shaded circle or square indicates that they are carriers lines are drawn to indicated matings, parent-offspring relationships, and relationships between siblings.

Inheritance Patterns Pedigree Example Unaffected Female

Inheritance Patterns Patterns of inheritance in a pedigree are different according to what type of trait is being studied. Remember your differences between the inheritance of completely dominant traits, autosomal traits and sex- linked traits to help determine inheritance patterns.

Inheritance Patterns Tips to identifying the inheritance on a pedigree: 1. Autosomal vs. Sex-linked: look at the number of affected males vs. affected females. Remember that females that are affected must have an affected father. Recessive vs. dominant: look at the occurrence, is it present in every generation or does it skip generations. Carriers are not always identified but if they are they indicate that the trait is caused by a recessive allele.

Inheritance Patterns One purpose of a pedigree is to track the inheritance of genetic disorders in a family. Genetic disorders fall into two categories: Autosomal (carried on the first 22 chromosomes) Sex-linked (carried on the X or Y chromosomes)

Genetic Disorders Disorders are inherited in a pattern specific to the disorder: Recessive Disorders: caused by recessive alleles Dominant Disorders: caused by dominant alleles Codominant Disorders: caused by multiple allele interactions (very complicated!) Sex-linked Disorders: caused by alleles carried on the X or Y chromosome

Genetic Disorders Cystic Fibrosis: caused by mutations to the CFTR gene on chromosome 7. Due to a defective protein in plasma membrane, thick mucus collects in the lungs and digestive tract Symptoms: delayed growth, coughing, nasal congestion, loss of apetite, frequent pneumonia Treatment: medication to minimize the effects of CF, there is no cure and the disease can result in death Recessive Disorder

Genetic Disorders Tay Sachs: disorder caused by a mutation in the HEXA gene on chromosome 15 Destroys nerve cells in the brain and spinal cord Most severe form affects infants and begins showing symptoms at 3-6 months. Children with severe infancy Tay Sachs rarely live more than 10 years. Recessive disorder

Genetic Disorders Phenylketonuria (PKU): mutation of the PAH genee on chromosome 12 that causes a lack of an enzyme needed to breakdown phenylalanine, an amino acid found in protein foods Symptoms: delayed mental and social abilities, jerking movements, seizures Tested for using a blood test performed on all newborn babies Treatable with a lifelong diet regimen Recessive disorder

Genetic Disorders Sickle cell anemia (autosomal): disorder that causes abnormal formation of hemoglobin (blood cells) because of mutations to the HBB gene on chromosome 11 Symptoms: Fatigue, paleness, rapid heart rate, shortness of breath, painful joints Treatment: Folic acid supplements, blood transfusions Codominant disorder Normal Cell Sickle Cell

Genetic Disorders Achondroplasia: disorder of bone growth that causes the most common form of dwarfism (can also be caused by spontaneous mutation) due to mutations in the FGFR3 gene on chromosome 4 Symptoms: short stature, spinal curvature, bowed legs, decreased muscle tone Treatment: none Dominant disorder Kenadie Jourdin-Bromley, 7 pounds at age 2 with father Court / Primordial Dwarfism

Genetic Disorders Huntington’s disease: disorder that causes a degeneration of nerve cells in parts of the brain because of a repeated section of CAG in the DNA on chromosome 4 Symptoms: paranoia, hallucinations, uncontrolled movements, loss of memory, speech changes Treatment: none This disease is lethal and there is currently no way to slow the development of symptoms as the disorder progresses Dominant disorder

Genetic Disorders Some genetic disorders are not the result of inheritance but instead are the result of chromosomes that do not correctly separate during meiosis Nondisjunction: failure of chromosomes to correctly separate during meiosis; NOT inherited from parents

Genetic Disorders Nondisjunction can result in various forms of chromosome abnormalities depending on how the chromosomes separated during meiosis: Trisomy: 3 copies of the same chromosome Monosomy: only 1 copy of a chromosome Duplication: a repeated section of the DNA strand for a gene (caused by sections of a chromosome that separate and reattach during crossing over)

Genetic Disorders Determining disorders caused by nondisjunction requires analysis of the chromosomes using a karyotype Karyotype: map of chromosomes

Human Chromosomes Normal Male Normal Female

Human Chromosomes Sex Chromosomes: 2 chromosomes that determine sex (either x or y) Males: xy Females: xx Autosomes: “rest” of chromosomes

Nondisjunction disorders Downs Syndrome: disorder caused by 3 chromosomes on pair #21 Symptoms: intellectual disabilities, changes in physical appearance Treatment: none

Nondisjunction disorders Klinefelters Syndrome: disorder that results in an extra X chromosome in males (XXY) Symptoms: sterile, rounded figure, weak bones

Nondisjunction disorders Extra Y syndrome: disorder that results in an extra Y chromosome in the sex chromosomes Typically shows no major physical differences except for a taller than average stature and remains fertile Some cases indicate there is a risk for learning disabilities and low muscle tone

Nondisjunction Disorders Metafemale Syndrome (Triple X): disorder where females receive an extra X chromosome Results in language learning disabilities, taller stature, low muscle tone, clinodactyly (pinkies curved toward the ring finger)

Nondisjunction Disorders Turners Syndrome: disorder that results in only 1 X chromosome Symptoms: higher incidence of heart disorders, very short (under 4’11’’), sterile, low set hairline and ears Treatment: none