Analyzing Human Inheritance

How Can We Study Human Inheritance? Pedigrees are graphic representations of an individual’s family tree Used to predict the chances of an offspring receiving a trait Used to determine the inheritance pattern of a particular trait

Pedigrees

Pedigree Symbols Normal Male Normal Female Affected Male Affected Female Mating Siblings Known Carriers

Inherited Genetic Disorders Cystic Fibrosis (CF) Caused by a recessive allele A missing membrane protein causes mucous build up in places like the lungs Most common among Caucasions

Inherited Genetic Disorders Sickle-cell Anemia Caused by a codominant allele An altered hemoglobin protein changes the shape of the red blood cells Most common among African-Americans

Inherited Genetic Disorders Tay-Sachs Caused by a recessive allele A missing enzyme causes lipid build up in the brain (death by age 4) Most common among eastern European Jews

Inherited Genetic Disorders Huntington’s Caused by a dominant allele Late-onset of symptoms (age 40) result in the deterioration of the nervous system

Inherited Genetic Disorders Phenylketonuria (PKU) Caused by a recessive allele A missing enzyme prevents the break down of phenylalanine (the build up can cause brain damage) If caught early, an altered diet can prevent damage

Analyzing Chromosomes

Analyzing Chromosomes A karyotype is an ordered display of an individual’s chromosomes Scientists take a picture of the chromosomes during metaphase

Analyzing Chromosomes Each chromosome is paired with its homologue The display is used to detect chromosomal abnormalities

How Do Chromosomal Abnormalities Occur? During (meiosis) cell division, sometimes chromosomes fail to separate correctly Nondisjunction This produces gametes with incorrect numbers of chromosomes

Meiotic Nondisjunction

Results of Nondisjunction Two types of zygotes can result from nondisjunction: Trisomy Zygote has 3 copies of a chromosome Monosomy Zygote only has 1 copy of a chromosome

Chromosomal Abnormalities Down Syndrome Caused by a trisomy 21 Most common serious birth defect in the U.S.

Chromosomal Abnormalities Klinefelter Syndrome Caused by an extra X chromosome in males (ex. XXY)

Chromosomal Abnormalities Jacobs or Extra Y Caused by an extra Y chromosome in males (ex. XYY)

Chromosomal Abnormalities Metafemale or Triple X Caused by an extra X chromosome in females (ex. XXX) Turner Syndrome Caused when females only get one X chromosome (XO) This is the only viable human monosomy

Prenatal Genetic Testing