Molecular Biology and Genetics

Molecular Biology and Genetics Genetics the scientific study of heredity and variation Heredity the transmission of traits from one generation to the next Brainpower Read More Gregor Mendel Father of Genetics; Studied inheritance of traits in pea plants. He found that plants' offspring retained traits of the parent particulate inheritance Mendel stated that physical traits are inherited as "particles" Trait any characteristic that can be passed from parent to offspring Alleles alternative forms of a gene Dominant stronger of the two genes expressed in the hybrid; represented by a capital letter Recessive gene that shows up less often in a cross; represented by a lower case Genotype gene/allele combination for a trait (e.g. RR, Rr, rr) Phenotype the physical feature resulting from a genotype (e.g red, white) Homozygous gene combination involving two dominant or two recessive genes (e.g RR or rr); also called pure or true breed Heterozygous gene combination of one dominant and one recessive allele (e.g Rr); also called as hybrid Monohybrid cross a cross involving single trait (e.g. flower color) Dihybrid cross cross involving two traits (e.g. flower color and plant height) Punnett Square A square diagram named after Reginald C. Punnett used to predict the genotypes of a particular cross or breeding experiment Parental P1 Generation the parental generation in a breeding experiment. PPxpp F1 generation the first generation offspring in a breeding experiment (1st filial generation) F2 generation Offspring resulting from interbreeding of the hybrid F1 generation. P1 Monohybrid Cross Homozygous dominant x Homozygous recessive RR x rr Offspring is all Heterozygous (Hybrids) Offspring is called F1 generation Genotypic and Phenotypic ratio are ALL ALIKE F1 monohybrid cross Heterozygous x Heterozygous Rr x Rr Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous recessive rr Offspring is called F2 generation Genotypic ratio: 1:2:1 Phenotypic ratio: 3:1 test cross a tool to determine an unknown genotype There are two possible test crosses: Homozygous dominant x Hybrid (RRxRr) Homozygous recessive x Hybrid (rrxRr) Test cross : Homozygous dominant x Hybrid (RRxRr) Test cross: Homozygous recessive x Hybrid (rrxRr) Law of Dominance (complete dominance) Mendel's first law that states that in a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Law of segregation Mendelian law stating that two alleles for each trait separate during meiosis; Alleles for a trait will then "recombine" at fertilization producing the genotype for the traits of the offspring Law of independent assortment Alleles for different traits are distributed to sex cells (and offspring) independently of one another; Inheritance of one trait does not affect inheritance of the other = law of independent assortment. This law is best illustrated using a Dihybrid Cross Dihybrid Cross Example (RrYy x RrYy) Genotype: RRYY, RRYy, RrYY, RrYy, Rryy, rrYY, rrYy, rryy Phenotype: Round Yellow, Round green, wrinkled Yellow, wrinkled green