BIO101 Chapter 12a - Inheritance 1 PDF

Today Particulate vs. blending inheritance Mendel’s experiments Dominant vs. recessive traits Mendel’s 3 principles of inheritance Punnett squares Before Next Class Study for Exam 3!  Chapter 12.1: Mendelian Inherita...

Today Particulate vs. blending inheritance Mendel’s experiments Dominant vs. recessive traits Mendel’s 3 principles of inheritance Punnett squares Before Next Class Study for Exam 3!  Chapter 12.1: Mendelian Inheritance Gregor Johann Mendel 1822–1884  Before Mendel Selective breeding of animals and plants Traits would sometimes appear and disappear later Two Theories of Inheritance Blending Particulate  Mendel studied the garden pea Lots of easily studied characters – true-breeding traits Large numbers of offspring Short generation times Easy to self- and cross-fertilize Fertilization: Crossing and Selfing  Monohybrid Cross Breed two parental (P) strains True-breeding round seed True-breeding wrinkled seed All F1 offspring are heterozygous for the gene in question. Examine F1 offspring to determine dominant trait.  The Results Mendel’s Principle of Uniformity/Dominance Trait that appears in all F1 seeds is dominant. Other trait is recessive and shows up in 25% of F2 seeds. Mendel’s Results from Monohybrid Crosses  Key Terms and Concepts Each gamete is haploid. When gametes fuse, they produce a diploid zygote. Each “unit of inheritance” is a gene. Different forms of a gene are called alleles. Diploid cells have two copies of a gene. Homozygous for a gene → two identical alleles (e.g., RR or rr) Heterozygous for a gene → two different alleles (e.g., Rr) Phenotype: observable traits of an individual (e.g., round, wrinkled, green) Genotype: genetic makeup of an organism or cell, usually indicated by two letters for each gene, with each letter representing an allele (RR, rr, R, r, RrYY)  Mendel’s Principle of Segregation 2 copies of a gene separate during gamete formation. Each gamete receives only 1 copy. Meiosis Accounts for Segregation  What’s a test cross? Is an individual with a dominant trait homozygous or heterozygous for that trait? Cross the individual with a homozygous recessive individual Examine traits of the offspring All dominant → unknown individual was homozygous ∼Half dominant, half recessive → unknown individual was heterozygous Mendel’s Principle of Independent Assortment Alleles of different genes assort independently of one another during gamete formation. Basically, the principle of segregation applies to each gene independent of other genes. Supported by a 9:3:3:1 ratio of traits in the F2 generation from a dihybrid cross Only works if genes are on different chromosomes!  Mendel’s Principle of Independent Assortment Dihybrid cross Breed two parental (P) strains that are true-breeding for 2 different traits All F1 offspring are heterozygous for both genes. 9:3:3:1 ratio of F2 offspring traits shows that the two genes assorted independently.  Meiosis and Independent Assortment https://media.saplinglearning.com/priv/he/bio/life12e/Life12e_resources/Animations/Animation_12.1_Independent_Assortment_of_Alleles.html