Genes – pieces of DNA that code for a particular character or trait MENDEL’S THEORY Genes – pieces of DNA that code for a particular character or trait

Mendel’s Theory of Heredity: 1. For each inherited trait, an individual has two copies of the gene – one from each parent. 2. There are alternative versions of these genes – the different versions of the gene are called alleles. 3. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organisms appearance. dominant – the expressed form of a trait recessive – the trait not expressed, unless two are present

4. When gametes are formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited trait. When gametes unite during fertilization, each gamete contributes one allele.

The Laws of Heredity: 1. Law of Segregation – states that the two alleles for a character or trait segregate (separate) when gametes are formed 2. Law of Independent Assortment - states genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another 3. Law of Dominance – states an organism with alternate forms of a gene will express the form that is dominant.

Vocabulary: dominant traits – are expressed by writing the first letter of the trait as an uppercase letter ex: purple flower - P recessive traits – are expressed by writing the first letter of the dominant trait but as a lowercase letter ex: white flower - p

Selecting Your Alleles: Height: tall is dominant; short is recessive Eye color: brown is dominant; green is recessive Hair: curly is recessive; straight is dominant T t B b s S

More Vocabulary: homozygous – the two alleles of a particular gene are the same ex: PP or pp heterozygous – the two alleles of a particular gene are different ex: Pp genotype – the set of alleles (genes) for a trait ex: PP, Pp, pp phenotype - the physical appearance of a trait ex: purple flower, white flower

Genotype or Phenotype? PP Red hair Yellow seeds Rr Dimples Tt Yy ss Short PP Yellow seeds Dimples Yy Set of alleles P G G P G P G G P G

Practice: For each genotype below, indicate whether it is heterozygous (He), homozygous (HO D) or (HO r) Rr ______ HH _______ ii ______ Ww _______ For each genotype below determine what phenotypes would be possible. Curly hair is dominant to straight hair. Cc ________ CC _________ cc ________ He HO D HO r He Curly Curly Straight

Practice: For each phenotype below, list the genotypes. Remember to use the letter of the dominant trait. Green eyes are dominant to blue eyes. ______ green eyes _______ blue eyes ______ green eyes GG gg Gg