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Reproduction, Heredity, and Variation I. Reproduction A. Overview:

Reproduction, Heredity, and Variation I. Reproduction A. Overview: - types of organismal reproduction – asexual reproduction (typically by mitosis). Heredity, Gene Regulation, and Development I. Reproduction Overview

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Reproduction, Heredity, and Variation I. Reproduction A. Overview:

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  1. Reproduction, Heredity, and Variation I. Reproduction A. Overview: - types of organismal reproduction – asexual reproduction (typically by mitosis)

  2. Heredity, Gene Regulation, and Development • I. Reproduction • Overview • - types of organismal reproduction – sexual reproduction – specialized cells (gametes) • - 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

  3. Reproduction • Overview • B. Costs and Benefits of Asexual and Sexual Reproduction

  4. Heredity, Gene Regulation, and Development • I. Reproduction • Overview • B. Costs and Benefits of Asexual and Sexual Reproduction

  5. Heredity, Gene Regulation, and Development • I. Reproduction • Overview • B. Costs and Benefits of Asexual and Sexual Reproduction

  6. Heredity, Gene Regulation, and Development • I. Reproduction • Overview • B. Costs and Benefits of Asexual and Sexual Reproduction

  7. I. Reproduction • A. Overview • Costs and Benefits of Asexual and Sexual Reproduction • Mixing Genomes • 1. HOW? • - problem: fusing body cells doubles genetic information over generations 2n 2n 4n 4n 8n

  8. I. Reproduction • Overview • Costs and Benefits of Asexual and Sexual Reproduction • Mixing Genomes • 1. HOW? • - problem: fusing body cells doubles genetic information over generations • - solution: make specialized cells with ½ the genetic info… have them fuse 1n 1n 2n 2n 2n ZYGOTE (offspring) GAMETES (egg and sperm)

  9. II. Meiosis and the Chromosomal Theory • Overview • Costs and Benefits of Asexual and Sexual Reproduction • Mixing Genomes • Meiosis • 1. Overview REDUCTION DIVISION 1n 1n 1n 1n 1n 1n 2n

  10. Reproduction • A. 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 Each cell is 1n = 2 2n = 4

  11. INDEPENDENT ASSORTMENT IN MEIOSIS I CREATES MANY COMBINATIONS OF GENES/CHROMOSOMES IN GAMETES A A a a b B b B OR a A A a B b b B

  12. Reproduction • A. 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 A A A b b b 1n = 2 Both are 1n = 2 NO CHANGE IN GENETIC CONTENT IN MEIOSIS II; IT IS SIMPLY DIVISIONAL, LIKE MITOSIS

  13. 5. Modifications in anisogamous and oogamous species In females, the chromosomes separate equally but the cytoplasm divides unequally; so only one function gamete is produced. However, it can be of any genetic type. Across multiple eggs, many types are produced.

  14. Reproduction • Variation

  15. Reproduction • Variation and Heredity • Sexual reproduction produces variation two ways: • 1. For one trait, it may combine different alleles for that trait. AA x aa Gametes: A + a Aa This combination didn’t exist before.

  16. Reproduction • Variation and Heredity • Sexual reproduction produces variation two ways: • For one trait, it may combine different alleles for that trait. • For multiple genes/loci, it create new combinations of genes that didn’t exist before. • AABB x aabb • Gametes: AB + ab = AaBb x AaBb • Gametes: AABB AABb AAbb AaBB AaBb Aabb aaBB aaBb aabb New combinations of genes that didn’t exist before!!! AB AB Ab Ab aB aB Ab ab x =

  17. Reproduction • 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

  18. Reproduction • Variation Consider an organism with 2n = 6 (AaBbCc) …. There are 2n = 8 different gamete types. ABC abc Abc abC aBC Abc AbC aBc

  19. Reproduction • Variation 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.

  20. Reproduction • Variation • Heredity

  21. A. Overview: 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) Environment GENOME A a PHENOTYPE

  22. A. Overview: B. Intralocular Interactions A a

  23. A. Overview: B. Intralocular Interactions 1. Complete Dominance: - The presence of one allele is enough to cause the complete expression of a given phenotype.

  24. A. Overview: B. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: - The heterozygote expresses a phenotype between or intermediate to the phenotypes of the homozygotes.

  25. A. Overview: B. 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 Phenotype Genotypes A AA, AO B BB, BO O OO AB AB codominance AB Phenotype

  26. A. Overview: B. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: 4. Overdominance : – the heterozygote expresses a phenotype MORE EXTREME than either homozygote “t” “T” Enzyme Activity Enzyme Activity TEMP TEMP TT = tall (grows best in warm conditions) tt = short (grows best in cool conditions) Tt = Very Tall (has both alleles and so grows optimally in cool and warm conditions)

  27. A. Overview: B. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: 4. Overdominance : 5. Lethal Alleles: - Essential genes: many proteins are required for life. “Loss-of-function” alleles may not affect heterozygotes, but in homozygotes may result in the death of the zygote, embryo, or adult – depending on when they should be expressed during development.

  28. I. Allelic, Genic, and Environmental Interactions A. Overview: B. Intralocular Interactions 1. Complete Dominance: 2. Incomplete Dominance: 3. Codominance: 4. Overdominance : 5. Multiple Alleles: - not really an interaction, but a departure from simple Mendelian postulates. - and VERY important as a source of variation

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