Fundamentals of Genetics Ch.9

(9-1) Genetics Field of Bio focused on how characteristics are passed from parent to offspring (heredity) Gregor Mendel “Father of Genetics”

Mendel’s Peas Studied 7 characteristics (heritable features) of peas Ex: plant height Each characteristic had 2 different traits Ex: long or short stems

Mendel’s Experiments Started w/ 2 pure plant groups for a particular characteristic P generation Cross-pollinated (sexual reprod.) those plants to produce the next generation F1 generation

Experiments (cont.) Allowed F1 plants to self-pollinate (asexual) to produce the next generation F2 generation

Mendel’s Results F1 always showed only 1 of the 2 traits Dominant factor: masked other trait F2 always showed a 3:1 ratio b/w the 2 traits Recessive factor: factor being masked

Mendel’s Laws Segregation Independent Assortment

Law of Segregation A pair of factors separate during gamete (sex cell) formation

Law of Independent Assortment Factors for different characteristics are distributed to gametes independently Ex: not all blue eyed people have blond hair

Molecular Genetics Study of the structure & function of chromo.’s & genes Allele: alternate form of a gene Dominant = capital letter (B) Recessive = lower case letter (b)

(9-2) Genetic Crosses Genotype: genetic makeup BB, Bb, bb Phenotype: physical appearance Not all alleles shown BB = black, Bb = black, bb = white

Genotype Vocab Homozygous (purebred): same alleles for the characteristic BB = ho/go dominant bb = ho/go recessive Heterozygous (Hybrid): different alleles for the characteristic Bb

Probability Likelihood that a specific event will occur Determined by a Punnett square

Punnett Squares Monohybrid Cross – 1 characteristic Dihybrid Cross – 2 “ Trihybrid Cross – 3 “

Testcross Dominant phenotype, but what genotype? Unknown genotype crossed w/ ho/go recessive

Complications Incomplete dominance Codominance Multiple alleles Pleiotropy Polygenic Inheritance Epistasis

Incomplete Dominance Both alleles blend to make phenotype Ex: red (RR) x white (rr) = pink (Rr)

Codominance Both alleles expressed in a he/go offspring No blending! Ex: red (RR) x white (rr) = roan (Rr) Roan = red & white

Multiple-alleles Traits controlled by 3 or more alleles of the same gene Blood groups (A, B, O)

Pleiotropy 1 gene affects many characters Hemoglobin sickling allele

Polygenic Traits 1 trait determined by multiple genes Skin color

Epistasis Expression of 1 gene depends on another Hair color & albinism genes