Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
A. 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
A. 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
A. Overview
- types of organismal reproduction – sexual reproduction
- fusion of specialized cells - gametes
Multiple mating types (‘sexes’) isogamy anisogamy
Usually just two types, but sometimes a range
( Chlamydamonas ) oogamy
Males and females

Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
A. 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
A. 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
A. 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
Photoby icmoore: http://www.wunderground.com/blog/icmoore/comment.html?entrynum=9&tstamp=&page=9
Protandry: male then female

Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
Asexual (copying existing genotype) Sexual (making new genotype)
Benefits
1) No mate need
2) All genes transferred to every offspring
3) Offspring survival high in same environment

Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
Asexual (copying existing genotype) Sexual (making new genotype)
Benefits
1) No mate need
2) All genes transferred to every offspring
3) Offspring survival high in same environment
Costs
1) “Muller’s ratchet”
2) Mutation (rare) only source of variation
3) Offspring survival is “all or none” in a changing environment

Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
Asexual (copying existing genotype) Sexual (making new genotype)
Benefits
1) No mate need
2) All genes transferred to every offspring
3) Offspring survival high in same environment
Costs
1) “Muller’s ratchet”
2) Mutation (rare) only source of variation
3) Offspring survival is “all or none” in a changing environment
Costs
1) May need to find/acquire a mate
2) Only ½ genes to each offspring
3) Offspring variable – many combo’s bad

Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
Asexual (copying existing genotype) Sexual (making new genotype)
Benefits
1) No mate need
2) All genes transferred to every offspring
3) Offspring survival high in same environment
Costs
1) “Muller’s ratchet”
2) Mutation (rare) only source of variation
3) Offspring survival is “all or none” in a changing environment
Costs
1) May need to find/acquire a mate
2) Only ½ genes to each offspring
3) Offspring variable – many combo’s bad
Benefits
1) Not all genes inherited – no ratchet
2) MUCH more variation produced
3) 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
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
Asexual (copying existing genotype) Sexual (making new genotype)
Benefits
1) No mate need
2) All genes transferred to every offspring
3) Offspring survival high in same environment
Costs
1) “Muller’s ratchet”
2) Mutation (rare) only source of variation
3) Offspring survival is “all or none” in a changing environment
Costs
1) May need to find/acquire a mate
2) Only ½ genes to each offspring
3) Offspring variable – many combo’s bad
Benefits
1) Not all genes inherited – no ratchet
2) MUCH more variation produced
3) 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
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
C. 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
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
C. Mixing Genomes
1. HOW?
- problem: fusing body cells doubles genetic information over generations
- solution: alternate fusion of cells with the reduction of genetic information
Fusion (fertilization)
1n 2n
Reduction (meiosis)

B. Mixing Genomes
1. HOW?
2. WHEN?
Zygotic meiosis: Fungi, some protists

B. Mixing Genomes
1. HOW?
2. WHEN?
Gametic meiosis: Animals

B. Mixing Genomes
1. HOW?
2. WHEN?
Sporic meiosis: Plants, some fungi

II. Meiosis and the Chromosomal Theory
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
C. Mixing Genomes
D. Meiosis
1. Overview
REDUCTION DIVISION
2n
1n
1n
1n
1n
1n
1n

II. Meiosis and the Chromosomal Theory
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
C. Mixing Genomes
D. 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
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
C. Mixing Genomes
D. 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
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
C. Mixing Genomes
D. Meiosis
E. Sexual Reproduction and Variation
1. Meiosis and Mendelian Heredity: The chromosomal theory of inheritance

D. Meiosis
E. 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

AB
D. Meiosis
E. 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
A a
Theodor Boveri
OR ab Ab aB
B b b B
Walter Sutton

D. Meiosis
E. 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 2 n or

D. Meiosis
E. 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 2 n = 8 different gamete types.
ABC
Abc aBC
AbC abc abC
Abc aBc

D. Meiosis
E. 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 2 n = 8 different gamete types.
And humans, with 2n = 46?

D. Meiosis
E. 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 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 of a single pair of mating humans.

D. III. Meiosis
E. 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
Independent Assortment  VARIATION 
Causes of Change
NATURAL SELECTION