12.1 Mendelian Inheritance of Human Traits
I. Making a pedigree
• Family tree—traces a family name and various family members through successive generations.
A. pedigrees illustrated inheritance
• a pedigree is a graphic representation of genetic inheritance
• Diagram made up of a set of symbols that identify males and females, individuals affected by trait.
• In a pedigree, a circle represents a female; a square represents a male.
• Unshaded circles and squares designate individuals that do not show the trait.
• A half-shaded circle or square represents a carrier- a heterozygous individual.
• Horizontal line: parents--- vertical line: offspring---horizontal row: generation—most recent generation: on the bottom
B. analyzing a pedigree
• By studying the pedigree, the individual will be able to determine the likelihood that she carries the allele.
II. Simple Recessive Heredity
• Most genetic disorders are caused by recessive alleles.
A. cystic fibrosis
• a fairly common genetic disorder among white Americans
• This is due to a defective protein in the plasma membrane—results in the formation and accumulation of thick mucus in the lungs and digestive tract.
B. tay-sachs disease
• A recessive disorder of the central nervous system.
• Common in the U.S. among ashkenazic Jews.
• Also called PKU, is a recessive disorder that results from the absence of an enzyme that converts one amino acids, phenylalanine, to a different amino acid, tyrosine.
• Common in the U.S. for Norway, Sweden, or Ireland.
• Fetus: the developing baby.
III. Simple Dominant Heredity
• A single dominant allele inherited from one parent is all that is needed for a person to show the dominant trait.
A. simple dominant traits
• cleft chin