Monohybrid & Dihybrid Inheritance Handout

**HANDOUT \#1** **MONOHYBRID & DIHYBRID INHERITANCE** **Monohybrid Inheritance --** is the inheritance of characteristics controlled by a single gene (mono = one). **[Alleles]** -- are the different variations of the same gene and they determine a single characteristic. - Homozygous Alleles --...

**HANDOUT \#1** **MONOHYBRID & DIHYBRID INHERITANCE** **Monohybrid Inheritance --** is the inheritance of characteristics controlled by a single gene (mono = one). **[Alleles]** -- are the different variations of the same gene and they determine a single characteristic. - Homozygous Alleles -- AA or aa - Heterozygous Alleles -- Aa **[Genotype]** -- refers to the two alleles an organism has inherited for a particular gene. A genotype could be: - Homozygous recessive -- is inheriting the same allele from both parents (rr) - Homozygous dominant - is inheriting the same allele from both parents (RR) - Heterozygous -- is a phenomenon in which 2 different alleles are inherited (Rr) **[Dominant]** -- a dominant gene allele is expressed when [either one or both is present]. A dominant allele overrules a recessive allele. (Example: if a plant has one or two dominant alleles, it will be purple) **[Recessive]** -- a recessive gene allele is expressed only when [both are present.] (Example: if a plant has two recessive alleles, it will be white) **[Phenotype]** -- is a result of the expression of one or more genes. A phenotype could be: brown hair, AB blood type, blue eye color **[Punnett Square]**- is a table in which all of the possible outcomes for a genetic cross between 2 individuals with known genotypes are given. Punnett square - Labster Example: In pea plants, purple flowers are dominant over white flowers, which are recessive. Cross two homozygous dominant (PP) parents. **Parental Cross: PP x PP**  **Genotypic Ratio:** 4 PP : 0 Pp : 0 pp **Phenotypic Ratio:** 4 purple flowers : o white flower **Genotype:** 100% PP **Phenotype:** 100% Purple Flowers **MENDEL'S LAW** 1. **Law of Dominance --** when parents with pure, contrasting traits are crossed together, ONLY ONE form of trait appears in the next generation. 2. **Law of Segregation** - states that alleles segregate RANDOMLY into gametes. 3. **Law of Independent Assortment --** the alleles for one trait segregate independently of the alleles for another trait. **DIHYBRID INHERITANCE --** refers to the inheritance of two genes that determine the expression of two different characteristics or influence the same characteristic. Example In rabbits, gray hair is dominant (G) to white hair (g). Also in rabbits, black eyes are dominant (B) to red eyes (b). A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype ggBB. Create a Punnett square to predict the possible outcome of the cross. Parental Cross: GGbb x ggBB **Genotypic Ratio** 1. GGBB : 16 GgBb : 0 ggbb