II. TRANSMISSION GENETICS Mendelian Inheritance Known as single-gene inheritance/unifactorial trait Gregor Mendel: “father of genetics” F rom crossed and catalogued 24,034 pea plants Why pea plants? E asy to grow D evelop quickly T raits with easily distinguishing forms (green-yellow, tall-short, round-wrinkled) continuous vs. discontinuous traits

Mendel’s Laws Law of Dominance: 1 gene (dominant) can mask the appearance of another gene (recessive) Law of Segregation: during formation of gametes alleles separate Aa A / a Law of Independent Assortment: during formation of gametes genes randomly arrange themselves AaBb AB / Ab / aB / ab Inheritance of a gene on 1 chromosome does not influence inheritance of a gene on a different chromosome Exception: Linkage (red hair-freckles)

Rules for Problem-Solving: Write down dominant and recessive genes Write down parents’ genes (P generation) Get parents’ gametes Do the cross on a punnett square (board for offspring possibilities – F 1 generation) Get results and label answer

Types of Problems: Simple 1 trait cross Monohybrid Cross (Ff X Ff)  Genotype: 1:2:1 Phenotype: 3:1 Simple 2 trait cross Dihybrid Cross (FfDd X FfDd)  Phenotype: 9:3:3:1 Incomplete Dominance (3 phenotypes present)  Andalusian Fowl FF (black) ff (white) Ff (blue)  Roan Cattle FF (brown/reddish) ff (white) Ff (brown with white)  Four O’Clock Flowers FF (red) ff (white) Ff (pink)

Pedigree Analysis Displays familial relationships and depicts which have specific phenotypes and genotypes Autosomal Dominant Trait: a trait can appear in either sex because an autosome carries the disease; do not skip generations Porphyria variegata: red urine, abdominal pain, coma, death Huntington Disease: progressive uncontrollable movements and personality change (begins in middle age) Polydactyly: extra fingers or toes Marfan Syndrome: long limbs, sunken chest, lens dislocation, weakened aorta

Autosomal Recessive Inheritance: can appear in either sex; Affected individuals with homozygous recessive genotype; can skip generations Cystic Fibrosis: lung infections and congestion Sickle Cell Anemia: joint pain, spleen damage Tay Sachs Disease: NS degeneration Phenylketonuria (PKU): fair skin, mental retardation Albinism: lack of melanin in skin, eyes, hair

Pedigree Information: Female = circle Male = square Parents – connected by a single line Consanguineous: parents are related (shown by a double line) Siblings’ ages read from left to right (older to younger) Arabic numbers = siblings Roman numerals = generations Twins represented by diagonal lines Identical Twins (monozygotic): horizontal line Fraternal Twins (dizygotic): no line