Bio 178 Lecture 23 Meiosis (Cntd.) and Genetics  J. Elson-Riggins

Reading Chapters 12, P , & 13 Quiz Material Questions on P 240, 1080, & Chapter 12, 50, & 13 Quizzes on Text Website (

Outline Meiosis (cntd.) Gametogenesis Genetics Mendelian Patterns of Inheritance Non-Mendelian Patterns of Inheritance

Mitosis Vs. Meiosis MITOSISMEIOSIS # Divisions # Daughter Cells Final Ploidy Cell Type Genetic Variation? Metaphase Alignment Anaphase Separation

Mitosis Vs. Meiosis MITOSISMEIOSIS # Divisions12 # Daughter Cells24 Final Ploidy2NN Cell TypeSomaticGametes Genetic Variation? NoYes Metaphase Alignment Chromosomes I - Homologues II - Chromosomes Anaphase Separation Sister chromatids I - Homologues II - Sister chromatids

Evolutionary Consequences of Sex Random Fertilization In addition to independent assortment and crossing over, random fertilization generates diversity because 2 gametes (each of which is different from the parent) fuse. Importance for Evolution The diversity generated by sexual reproduction results in individuals that may be fitter than others (not always!) in a particular environment and will therefore be selected by that environment.

Spermatogenesis

McGraw-Hill Video

Structure of Seminiferous Tubules

Structure of Sperm

Oogenesis Prophase I Metaphase II (Fertilization)

Mature Follicle (Metaphase II)

Initial Ideas About Heredity Pre-Mendel Read about classical assumptions (P 242) & the work of Koelreuter & Knight. Mendel ( ) What was different about Mendel’s work?

Mendel’s Experiments Characteristics of the Study Subject The garden pea was a good choice because: 1.Can cross or self-fertilize. 2.Produces large numbers of offspring. 3.Easy to grow. 4.Has a number of varieties with different traits. 5.Short generation times. 6.Produces hybrid varieties.

Mendel’s Experiments Experimental Design Mendel worked with 7 easily distinguishable traits as follows: 1. Ensured the parental (P) generation was true-breeding. Eg. White flowered plants  White flowered progeny 2. Crossed varieties with alternate traits. Eg.

Mendel’s Experimental Design (Cntd.) 3. Self-fertilized the hybrid generation (F 1 ) Mendel’s Results F 1 Generation No intermediate progeny - all resembled one of the parents. This was referred to as the dominant trait. Eg. P:Purple X White  F 1 :Purple

Mendel’s Results (Cntd.) F 2 Generation F 1 :Purple X Purple  F 2 :3 Purple : 1 White

Mendel’s Experiments (Cntd.) Self-fertilize the F 2  Disguised 1:2:1 Ratio

Mendel’s Experiments (Cntd.) Self-fertilize the F 2  Disguised 1:2:1 Ratio

Mendel’s Conclusions 1. Blending (hybridization) was not occurring. 2. For each alternative trait, one alternative was not expressed in the F 1, but reappeared in the F Pairs of alternate traits segregated among progeny of a particular cross. 4. These alternate traits were expressed in the F 2 generation as 3 dominant : 1 recessive.

Principles of Genetics Mendel’s ideas in modern terms: Genes Information about traits is transmitted from parent to offspring in the form of genes. Homologous Chromosomes A diploid individual receives 2 alleles (forms of a gene) for each trait, one on each of 2 homologous chromosomes. Homozygous Heterozygous