1. 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)

2. 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.

3. 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

4. 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

5. 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

6. 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:

7. 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

8. 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.

9. 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

10. 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

11. 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

12. 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

13. 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

14. 5. Modifications in anisogamous and oogamous species

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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?

21. 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.

22. 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