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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’)
Usually just two types,
but sometimes a range
(Chlamydamonas)
isogamy
anisogamy
Males and females
oogamy
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
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
A. Overview
B. Costs and Benefits of Asexual and Sexual Reproduction
Asexual (copying existing genotype)
Benefits
1) No mate need
2) All genes transferred to every offspring
3) Offspring survival high in same
environment
Sexual (making new genotype)
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)
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
Sexual (making new genotype)
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) May need to find/acquire a mate
2) Only ½ genes to each offspring
3) Offspring variable – many combo’s bad
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) May need to find/acquire a mate
2) Only ½ genes to each offspring
3) Offspring variable – many combo’s bad
Costs
1) “Muller’s ratchet”
2) Mutation (rare) only source of variation
3) Offspring survival is “all or none” in a
changing environment
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) May need to find/acquire a mate
2) Only ½ genes to each offspring
3) Offspring variable – many combo’s bad
Costs
1) “Muller’s ratchet”
2) Mutation (rare) only source of variation
3) Offspring survival is “all or none” in a
changing environment
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
1n
1n
1n
2n
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
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
Theodor Boveri
a
OR
AB
ab
B
b
Ab
aB
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
2n
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 2n = 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 2n = 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 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.
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
Causes of Change
 VARIATION 
NATURAL SELECTION