The science of genes, heredity and variation of organisms Genetics The science of genes, heredity and variation of organisms

History of Genetics Pioneered by Gregor Mendel. Mendel discovered basic principles of heredity by growing pea plants. He proposed that characteristics were inherited from parent plants, in the form of ‘hereditary factors’ otherwise known as genes.

Genetics Vocabulary Gene-Chromosome Theory: After Mendel’s work was re-discovered, microscopic examination of cells (no microscopes during Mendel’s time) and experiments in breeding fruit flies, proved a link between chromosomes, their movement in meiosis and Mendel’s ‘hereditary factors’.

Genetics Vocabulary Alleles: 2 genes which control each trait Dominance: If only one of the genes in a pair of alleles is expressed, or shown Recessive: The gene which is there but not expressed. A capital letter denotes dominant alleles, and lower case denotes recessive Ex: T (dominant) t (recessive)

More Vocabulary Genotype: The genetic makeup of an organism Homozygous: When both alleles are the same. Ex. TT or tt Heterozygous: When both alleles of the pair are different. Ex. Tt Phenotype: The appearance of the organism

Genetic Crosses Genetic Crosses look at traits in parents, organisms in their offspring. The organisms used to begin their studies are called the parent generations The first set of offspring are called the first filial or F1 generation. A cross between two F1’s gives us the second filial or F2 generation. Used for plants, flies and other animals.

Segregation and Recombination In Meiosis there is a random segregation (separation) of homologous chromosomes. Ex: Tt (Genotyotype of primary sperm cell or a primary pollen grain, ovule, egg, etc) Each gamete contains one allele for each trait. After the gametes fuse during fertilization, the resulting cell contains pairs of homologous chromosomes, but new combinations of alleles are present

Pesky Rule Breakers Intermediate Inheritance- Some genes are not clearly dominant or recessive. The heterozygous (RW) is different from the homozygous forms: (WW) and (RR).

Pesky Rule Breakers Incomplete Dominance: When the phenotype is a “blend” of the alleles present Notice 100% of offspring are a blend of white and red… PINK! R W RW

Pesky Rule Breakers Roan Colored Cattle Codominance: A type of intermediate inheritance where both alleles are expressed at the same time in the heterozygous individual. CR CR =Red Coat Cw Cw = White Coat CR Cw = Roan Coat Roan coat is a mix of red and white hairs Other examples- sickle cell anemia and blood groups Roan Colored Cattle

Multiple Alleles Multiple Alleles: When a trait is coded for by more than 2 different alleles Blood groups are coded for by multiple alleles Blood groups have 3 alleles IA = Type A allele IB = Type B allele i= Recessive allele

Blood Typing Type A blood: ______ or _______ Type B blood: _______ or ________ Type AB blood:_______ Type O blood: _______ Remember: The alleles for blood typing are codominant. Eye color is also expressed by multiple alleles!