Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview - types of organismal reproduction – asexual reproduction (typically by mitosis)
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview - types of organismal reproduction – sexual reproduction - conjugation in bacteria and some protists – gene exchange.
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview - types of organismal reproduction – sexual reproduction - fusion of specialized cells - gametes isogamy anisogamy oogamy Multiple mating types (‘sexes’) Usually just two types, but sometimes a range (Chlamydamonas) Males and females
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview - types of organismal reproduction – sexual reproduction - who produces these specialized reproductive cells? Hermaphrodism
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview - types of organismal reproduction – sexual reproduction - who produces these specialized reproductive cells? Monoecious plants Male and female flowers on the same individual plant
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview - types of organismal reproduction – sexual reproduction - who produces these specialized reproductive cells? Dioecious organisms: either male or female Sexes permanent Sex changes: Sequential hermaphrodism Progyny: female then male Protandry: male then female Photoby icmoore: http://www.wunderground.com/blog/icmoore/comment.html?entrynum=9&tstamp=&page=9
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview B. Costs and Benefits of Asexual and Sexual Reproduction Asexual (copying existing genotype) Sexual (making new genotype) Benefits No mate need All genes transferred to every offspring Offspring survival high in same environment Costs May need to find/acquire a mate Only ½ genes to each offspring Offspring variable – many combo’s bad “Muller’s ratchet” Mutation (rare) only source of variation Offspring survival is “all or none” in a changing environment Not all genes inherited – no ratchet MUCH more variation produced In a changing environment, producing variable offspring is very adaptive
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview B. Costs and Benefits of Asexual and Sexual Reproduction Asexual (copying existing genotype) Sexual (making new genotype) Benefits No mate need All genes transferred to every offspring Offspring survival high in same environment Costs May need to find/acquire a mate Only ½ genes to each offspring Offspring variable – many combo’s bad “Muller’s ratchet” Mutation (rare) only source of variation Offspring survival is “all or none” in a changing environment Not all genes inherited – no ratchet MUCH more variation produced In a changing environment, producing variable offspring is very adaptive And because all environments on earth change, sex has been adaptive for all organisms. Even those that reproduce primarily by asexual means will reproduce sexually when the environment changes. This is an adaptive strategy – it produces lots of variation.
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview Costs and Benefits of Asexual and Sexual Reproduction Mixing Genomes 1. HOW? - problem: fusing body cells doubles genetic information over generations 2n 4n 8n 2n 4n
Heredity, Gene Regulation, and Development I. Mendel's Contributions II. Meiosis and the Chromosomal Theory Overview Costs and Benefits of Asexual and Sexual Reproduction Mixing Genomes 1. HOW? - problem: fusing body cells doubles genetic information over generations - solution: produce specialized cells with ½ the genetic info = gametes 2n 1n 2n REDUCTION by meiosis 1n 2n
II. Meiosis and the Chromosomal Theory Overview Costs and Benefits of Asexual and Sexual Reproduction Mixing Genomes Meiosis: The production of specialized cells with ½ the chromosomes as parent 1. Overview REDUCTION DIVISION 1n 1n 1n 2n 1n 1n 1n
II. Meiosis and the Chromosomal Theory Overview Costs and Benefits of Asexual and Sexual Reproduction Mixing Genomes Meiosis 1. Overview 2. Meiosis I (Reduction) There are four replicated chromosomes in the initial cell. Each chromosomes pairs with its homolog (that influences the same suite of traits), and pairs align on the metaphase plate. Pairs are separated in Anaphase I, and two cells, each with only two chromosomes, are produced. REDUCTION
II. Meiosis and the Chromosomal Theory Overview Costs and Benefits of Asexual and Sexual Reproduction Mixing Genomes Meiosis 1. Overview 2. Meiosis I (Reduction) 3. Transition 4. Meiosis II (Division) Each cell with two chromosomes divides; sister chromatids are separated. There is no change in ploidy in this cycle; haploid cells divide to produce haploid cells. DIVISION
5. Modifications in anisogamous and oogamous species
II. Meiosis and the Chromosomal Theory Overview Costs and Benefits of Asexual and Sexual Reproduction Mixing Genomes Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory of inheritance
Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory Saw homologous chromosomes separating (segregating). If they carried genes, this would explain Mendel’s first law. A a Theodor Boveri Walter Sutton
Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory And if the way one pair of homologs separated had no effect on how others separated, then the movement of chromosomes would explain Mendel’s second law, also! They proposed that chromosomes carry the heredity information. A a Theodor Boveri A a OR AB ab Ab aB B b b B Walter Sutton
Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma 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 2n or
Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2n = 8 different gamete types. ABC abc Abc abC aBC Abc AbC aBc
Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2n = 8 different gamete types. And humans, with 2n = 46?
Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2n = 8 different gamete types. And humans, with 2n = 46? 223 = ~ 8 million different types of gametes. And each can fertilize ONE of the ~ 8 million types of gametes of the mate… for a total 246 = ~70 trillion different chromosomal combinations possible in the offspring of a single pair of mating humans.
III. Meiosis Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma 3. Model of Evolution – circa 1905 Sources of Variation Causes of Change Independent Assortment VARIATION NATURAL SELECTION