E. The Power of Independent Assortment 1. If you can assume that the genes assort independently, then you can calculate ‘single gene’ outcomes and multiply results together… 2. You can easily address more difficult multigene problems: (female) AaBbCcdd x AABbccDD (male) - how many types of gametes can each parent produce? - What is the probability of an offspring expressing ABCD? - How many genotypes are possible in the offspring? 2 x 3 x 2 x 1= 12 - how many phenotypes are possible in the offspring? 1 x 2 x 2 x 1 = 4 At A:At B:At C:At D: AA AAA aAa Bb BBBBb b bb c CCc ccc D dDd

E. The Power of Independent Assortment 1. If you can assume that the genes assort independently, then you can calculate ‘single gene’ outcomes and multiply results together… 2. You can easily address more difficult multigene problems. As you can see, IA produces lots of variation, because of the multiplicative effect of combining genes from different loci together in gametes, and then combining them together during fertilization… we’ll look at this again; especially with respect to Darwin’s 3 rd dilemma.

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: In sexually reproducing species, gametes carry exactly ½ the genetic information as the parent; so that the fusion of gametes reconstitutes the correct genetic complement. 2n = 4 1n = 2 Fertilization (fusion)

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: In sexually reproducing species, gametes carry exactly ½ the genetic information as the parent; so that the fusion of gametes reconstitutes the correct genetic complement. The divisional process that produces these special cells is called meiosis. Thus, meiosis ONLY occurs in reproductive tissue (ovary, testis), and only produces gametes. All other cells in multicellular organisms are produced by mitosis. 2n = 4 1n = 2 Fertilization (fusion) MEIOSIS DiploidHaploid

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: In sexually reproducing species, gametes carry exactly ½ the genetic information as the parent; so that the fusion of gametes reconstitutes the correct genetic complement. The divisional process that produces these special cells is called meiosis. Thus, meiosis ONLY occurs in reproductive tissue (ovary, testis), and only produces gametes. All other cells in multicellular organisms are produced by mitosis. MEIOSIS has two divisional cycles, “reduction” and “division” 2n = 4 1n = 2 Fertilization (fusion) MEIOSIS DiploidHaploid

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” - Prophase I: condensation in pairs possible crossing over

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” - Prophase I: condensation in pairs possible crossing over - Metaphase I: Homologs align In PAIRS

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” - Prophase I: condensation in pairs possible crossing over - Metaphase I: Homologs align In PAIRS - Anaphase I: Replicated chromosomes move to opposite poles

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” - Prophase I: condensation in pairs possible crossing over - Metaphase I: Homologs align In PAIRS - Anaphase I: Replicated chromosomes move to opposite poles - Telophase – Prophase II transition

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” - Prophase I: condensation in pairs possible crossing over - Metaphase I: Homologs align In PAIRS - Anaphase I: Replicated chromosomes move to opposite poles - Telophase – Prophase II transition PLOIDY REDUCED 2n parent cell  1n daughter cells

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” c. Meiosis II: “The Division Cycle” Like mitosis, but a haploid cell… chromsomes line up in single file in Metaphase II, and sister chromatids (of replicated chromosomes) separate and move to opposite poles.

F. WHY do these patterns occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” c. Meiosis II: “The Division Cycle” d. Variations in the Process: In spermatogenesis: Karyokinesis is equal and cytokinesis is equal, resulting in 4 equal-sized sperm.

F.WHY do these pattern occur? Meiosis: Gamete Formation a. Overview: b. Meiosis I: “The Reduction Cycle” c. Meiosis II: “The Division Cycle” d. Variations in the Process: In oogenesis, karyokinesis is equal (dividing the genetic information exactly in half), but cytokinesis is unequal, with one daughter cell getting the majority of the cytoplasm and organelles. The smaller may/may not be able to divide. These are ‘polar bodies’

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri Theodor Boveri Walter Sutton

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri Saw homologous chromosomes separating (segregating). If they carried genes, this would explain Mendel’s first law. Theodor Boveri Walter Sutton Aa

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri And if the way one pair of homologs separated had no effect on how others separated, then the mvmnt of chromosomes would explain Mendel’s second law, also! Theodor Boveri Walter Sutton Aa Aa bBBb ABabAbaB

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri This was a major achievement in science. The patterns of heredity had been associated with physical entities in biological cells. The movement of chromosomes correlated with Mendel’s patterns. Scientist now went about testing if this relationship was causal – and they found it was. Theodor Boveri Walter Sutton

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation Independent Assortment produces an amazing amount of genetic variation. Consider an organism, 2n = 4, with two pairs of homologs. They can make 4 different gametes (long Blue, Short Red) (Long Blue, Short Blue), (Long Red, Short Red), (Long Red, Short blue). Gametes carry thousands of genes, so homologous chromosomes will not be identical over their entire length, even though they may be homozygous at particular loci. Well, the number of gametes can be calculated as 2 n or

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2 n = 8 different gamete types. ABCabc AbcabC aBCAbc AbCaBc

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2 n = 8 different gamete types. And humans, with 2n = 46? ABCabc AbcabC aBCAbc AbCaBc

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2 n = 8 different gamete types. And humans, with 2n = 46? 2 23 = ~ 8 million different types of gametes. And each can fertilize ONE of the ~ 8 million types of gametes of the mate… for a total 2 46 = ~70 trillion different chromosomal combinations possible in the offspring. ABCabc AbcabC aBCAbc AbCaBc

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation Independent Assortment produces an amazing amount of genetic variation. And each can fertilize ONE of the ~ 8 million types of gametes of the mate… for a total 2 46 = 70 trillion different chromosomal combinations possible in the offspring. YOU are 1 of the 70 trillion combinations your own parents could have made. IA creates a huge amount of genetic variation, and that doesn’t include crossing over!!!!

III. Uniting Genetics and Cell Biology A. The Chromosomal Theory – Sutton and Boveri B. Solving Darwin’s Dilemma – The Source of Variation C. Modification to Evolutionary Theory Darwin’s Model Sources of VariationCauses of Change ????????????????  VARIATION  NATURAL SELECTION (use and disuse??)

III. Uniting Genetics and Cell Biology A. Early Studies B. Divisional Processes C. The Chromosomal Theory – Sutton and Boveri D. Solving Darwin’s Dilemma – The Source of Variation E. Modification to Evolutionary Theory Darwin’s Model Sources of VariationCauses of Change Independent Assortment  VARIATION  NATURAL SELECTION

IV. Modifications to Mendelian Patterns

- Overview: Mendels conclusions regarding dominance, equal segregation, independent assortment, and independent effects hold for many genes and traits. But they are not true of ALL traits.

IV. Modifications to Mendelian Patterns - Overview: Mendels conclusions regarding dominance, equal segregation, independent assortment, and independent effects hold for many genes and traits. But they are not true of ALL traits. Here, we will consider how the effect of a gene is influenced at three levels:

IV. Modifications to Mendelian Patterns - Overview: Mendels conclusions regarding dominance, equal segregation, independent assortment, and independent effects hold for many genes and traits. But they are not true of ALL traits. Here, we will consider how the effect of a gene is influenced at three levels: - Intralocular (effects of other alleles at this locus)

IV. Modifications to Mendelian Patterns - Overview: Mendels conclusions regarding dominance, equal segregation, independent assortment, and independent effects hold for many genes and traits. But they are not true of ALL traits. Here, we will consider how the effect of a gene is influenced at three levels: - Intralocular (effects of other alleles at this locus) - Interlocular (effects of other genes at other loci)

IV. Modifications to Mendelian Patterns - Overview: Mendels conclusions regarding dominance, equal segregation, independent assortment, and independent effects hold for many genes and traits. But they are not true of ALL traits. Here, we will consider how the effect of a gene is influenced at three levels: - Intralocular (effects of other alleles at this locus) - Interlocular (effects of other genes at other loci) - Environmental (the effect of the environment on determining the effect of a gene on the phenotype)

IV. Modifications to Mendelian Patterns - Overview: Mendels conclusions regarding dominance, equal segregation, independent assortment, and independent effects hold for many genes and traits. But they are not true of ALL traits. Here, we will consider how the effect of a gene is influenced at three levels: - Intralocular (effects of other alleles at this locus) - Interlocular (effects of other genes at other loci) - Environmental (the effect of the environment on determining the effect of a gene on the phenotype) And finally, we will examine the VALUE of an allele – are there “good genes” and “bad genes”?

IV. Modifications to Mendelian Patterns A. Intralocular Interactions A a

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: - The presence of one allele is enough to cause the complete expression of a given phenotype.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: - The heterozygote expresses a phenotype between or intermediate to the phenotypes of the homozygotes.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: - Both alleles are expressed completely; the heterozygote does not have an intermediate phenotype, it has BOTH phenotypes. Genotypic and phenotypic ratios of F1 x F1 crosses are both 1:2:1 ABO Blood Type: A = ‘A’ surface antigens

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: - Both alleles are expressed completely; the heterozygote does not have an intermediate phenotype, it has BOTH phenotypes. Genotypic and phenotypic ratios of F1 x F1 crosses are both 1:2:1 ABO Blood Type: A = ‘A’ surface antigens B = ‘B’ surface antigens

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: - Both alleles are expressed completely; the heterozygote does not have an intermediate phenotype, it has BOTH phenotypes. ABO Blood Type: A = ‘A’ surface antigens B = ‘B’ surface antigens O = no surface antigen from this locus

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: - Both alleles are expressed completely; the heterozygote does not have an intermediate phenotype, it has BOTH phenotypes. ABO Blood Type: A = ‘A’ surface antigens B = ‘B’ surface antigens O = no surface antigen from this locus PhenotypeGenotypes AAA, AO BBB, BOOAB codominance AB Phenotype

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: 4. Multiple Alleles: - While not really specifying an ‘interaction’, it does raise a complication of looking at a single trait.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: 4. Multiple Alleles: - While not really specifying an ‘interaction’, it does raise a complication of looking at a single trait. - You might presume that a ‘single-gene’ trait could only have a maximum of three phenotypes (AA, Aa, aa). But with many alleles possible for a gene (as for A,B,O), there are many diploid combinations and effects that are possible (as in the 4 phenotypes for the A,B,O system).

IV. Modifications to Mendelian Patterns A. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: 4. Overdominance – the heterozygote expresses a phenotype MORE extreme than either homozygote – see class notes.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions - Summary and Implications: populations can harbor extraordinary genetic variation at each locus, and these alleles can interact in myriad ways to produce complex and variable phenotypes.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions - Summary and Implications: populations can harbor extraordinary genetic variation at each locus, and these alleles can interact in myriad ways to produce complex and variable phenotypes. -Consider this cross: AaBbCcDd x AABbCcDD Assume: The genes assort independently A and a are codominant B is incompletely dominant to b C is incompletely dominant to c D is completely dominant to d How many phenotypes are possible in the offspring?

IV. Modifications to Mendelian Patterns A. Intralocular Interactions - Summary and Implications: populations can harbor extraordinary genetic variation at each locus, and these alleles can interact in myriad ways to produce complex and variable phenotypes. -Consider this cross: AaBbCcDd x AABbCcDD Assume: The genes assort independently A and a are codominant B is incompletely dominant to b C is incompletely dominant to c D is completely dominant to d How many phenotypes are possible in the offspring? ABCD 2x3 x3 x1 = 18 If they had all exhibited complete dominance, there would have been only: 1x2 x2 x1 = 4 So the variety of allelic interactions that are possible increases phenotypic variation multiplicatively. In a population with many alleles at each locus, there is an nearly limitless amount of phenotypic variability.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: one gene curtails the expression at another locus; the phenotype in the A,B,O blood group system can be affected by the genotype at the fucosyl transferase locus.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: one gene curtails the expression at another locus; the phenotype in the A,B,O blood group system can be affected by the genotype at the fucosyl transferase locus. This locus makes the ‘H substance’ to which the sugar groups are added to make the A and B surface antigens.

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: one gene curtails the expression at another locus; the phenotype in the A,B,O blood group system can be affected by the genotype at the fucosyl transferase locus. This locus makes the ‘H substance’ to which the sugar groups are added to make the A and B surface antigens. A non-function ‘h’ gene makes a non- functional foundation and sugar groups can’t be added – resulting in O blood regardless of the genotype at the A,B,O locus Genotype at H Genotype at A,B,O Phenotype H-A-A H-B-B H-OOO H-AB hhA-O hhB-O hhOOO hhABO

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: one gene curtails the expression at another locus; the phenotype in the A,B,O blood group system can be affected by the genotype at the fucosyl transferase locus. This locus makes the ‘H substance’ to which the sugar groups are added to make the A and B surface antigens. A non-function ‘h’ gene makes a non- functional foundation and sugar groups can’t be added – resulting in O blood regardless of the genotype at the A,B,O locus So, what are the phenotypic ratios from this cross: HhAO x HhBO?

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: -example #2: in a enzymatic process, all enzymes may be needed to produce a given phenotype. Absence of either may produce the same alternative ‘null’. Process: enzyme 1 enzyme 2 Precursor1 precursor2 product (pigment)

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: -example #2: in a enzymatic process, all enzymes may be needed to produce a given phenotype. Absence of either may produce the same alternative ‘null’. For example, two strains of white flowers may be white for different reasons; each lacking a different necessary enzyme to make color. Process: enzyme 1 enzyme 2 Precursor1 precursor2 product (pigment) Strain 1: enzyme 1 enzyme 2 Precursor1 precursor2 no product (white) Strain 2: enzyme 1 enzyme 2 Precursor1 precursor2 no product (white)

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: -example #2: in a enzymatic process, all enzymes may be needed to produce a given phenotype. Absence of either may produce the same alternative ‘null’. For example, two strains of white flowers may be white for different reasons; each lacking a different necessary enzyme to make color. So there must be a dominant gene at both loci to produce color. GenotypePhenotype aaB-white aabbwhite A-bbwhite A-B-pigment So, what’s the phenotypic ratio from a cross: AaBb x AaBb ?

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: -example #3: Novel Phenotypes. Comb shape in chickens is governed by 2 interacting genes that independently produce “Rose” or “Pea” combs, but together produce something completely different (walnut). GenotypePhenotype rrppsingle R-pprose rrP-pea A-B-Walnut

IV. Modifications to Mendelian Patterns A. Intralocular Interactions B. Interlocular Interactions: The genotype at one locus can influence how the genes at other loci are expressed. 1. Epistasis: 2. Polygenic Traits: There may be several genes that essentially produce the same protein product; and the phenotype is the ADDITIVE sum of these multiple genes. Creates continuously variable traits.