1. DON’T WORRY!! Just a photoshop award winner…
Heredity, Gene Regulation, and Development
I. Mendel's Contributions
II. Meiosis and the Chromosomal Theory
III. Allelic, Genic, and Environmental Interactions
IV. Sex Determination and Sex Linkage
V. Linkage
VI. Mutation
A. Overview
DON’T WORRY!! Just a photoshop award winner…

2. VI. Mutation Overview A change in the genome
Occurs at four scales of genetic organization:
1: Change in the number of sets of chromosomes ( change in ‘ploidy’)
2: Change in the number of chromosomes in a set (‘aneuploidy’)
3: Change in the number and arrangement of genes on a chromosome
4: Change in the nitrogenous base sequence within a gene

3. Some triploid babies are born alive, but die shortly after.
VI. Mutation
Overview
Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
Triploidy occurs in 2-3% of all human pregnancies, but almost always results in spontaneous abortion of the embryo.
Some triploid babies are born alive, but die shortly after.
Syndactyly (fused fingers), cardiac, digestive tract, and genital abnormalities occur.

4. VI. Mutation Failure of Meiosis I 2n = 4 Gametes: Overview
Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
Mechanism: Complete failure of Meiosis
- if meiosis fails, reduction does not occur and a diploid gamete is produced. This can occur because of failure of homologs OR sister chromatids to separate in Meiosis I or II, respectively.
Failure of Meiosis I
2n = 4
Gametes:

5. VI. Mutation Overview Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
Mechanism #1: Complete failure of Meiosis
- if meiosis fails, reduction does not occur and a diploid gamete is produced. This can occur because of failure of homologs OR sister chromatids to separate in Meiosis I or II, respectively.
- this results in a single diploid gamete, which will probably fertilize a normal haploid gamete, resulting in a triploid offspring.
negative consequences of Triploidy:
1) quantitative changes in protein production and regulation.
2) can’t reproduce sexually; can’t produce gametes if you are 3n.

6. Like this Blue-spotted Salamander A. laterale,
VI. Mutation
Overview
Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
Mechanism #1: Complete failure of Meiosis
negative consequences of Triploidy:
1) quantitative changes in protein production and regulation.
2) can’t reproduce sexually; can’t produce gametes if you are 3n.
3) but, some organisms can survive, and reproduce parthenogenetically (mitosis)
Like this Blue-spotted Salamander A. laterale,
which has a triploid sister species, A. tremblayi
A. tremblayi is a species that consists of 3n females that reproduce clonally – laying 3n eggs that divide without fertilization.

7. VI. Mutation Overview Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
Mechanism #1: Complete failure of Meiosis
Mechanism #2: Failure of Mitosis in Gamete-producing Tissue

8. 2n
1) Consider a bud cell in the flower bud of a plant.

9. 2n 4n
1) Consider a bud cell in the flower bud of a plant.
2) It replicates it’s DNA but fails to divide... Now it is a tetraploid bud cell.

10. 2n 4n
1) Consider a bud cell in the flower bud of a plant.
2) It replicates it’s DNA but fails to divide... Now it is a tetraploid bud cell.
3) A tetraploid flower develops from this tetraploid cell; eventually producing 2n SPERM and 2n EGG

11. 2n
1) Consider a bud cell in the flower bud of a plant. 4n
2) It replicates it’s DNA but fails to divide... Now it is a tetraploid bud cell.
3) A tetraploid flower develops from this tetraploid cell; eventually producing 2n SPERM and 2n EGG
4) If it is self-compatible, it can mate with itself, producing 4n zygotes that develop into a new 4n species.
Why is it a new species?

12. How do we define ‘species’?
“A group of organisms that reproduce with one another and are reproductively isolated from other such groups”
(E. Mayr – ‘biological species concept’)

13. How do we define ‘species’?
Here, the tetraploid population is even reproductively isolated from its own parent species…So speciation can be an instantaneous genetic event… 4n 2n
Gametes
Zygote 1n 3n
Triploid is a dead-end… so species are separate

14. VI. Mutation
Overview
Changes in Ploidy
- These are the most dramatic changes, adding a whole SET of chromosomes
Mechanism #1: Complete failure of Meiosis
Mechanism #2: Complete failure of Mitosis
The Frequency of Polyploidy
For reasons we just saw, we might expect polyploidy to occur more frequently in hermaphroditic species, because the chances of ‘jumping’ the triploidy barrier to reproductive tetraploidy are more likely. Over 50% of all flowering plants are polyploid species; many having arisen by this duplication of chromosome number within a lineage.

15. VI. Mutation Overview Changes in Ploidy
Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)

16. VI. Mutation Overview Changes in Ploidy
Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
a. trisomies
Trisomy 21 – “Downs’ Syndrome”

17. VI. Mutation Overview Changes in Ploidy
Changes in ‘aneuploidy’ (changes in chromosome number)
1. Mechanism: Non-disjunction (failure of a homologous pair or
sister chromatids to separate)
2. Human Examples
b. monosomies
45, XO– “Turner’s Syndrome” (the only human monosomy to survive to birth)

18. 1. Unequal Crossing-Over a. process: If homologs line up askew:
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Unequal Crossing-Over
a. process:
If homologs line up askew: A B a b

19. 1. Unequal Crossing-Over a. process: If homologs line up askew
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Unequal Crossing-Over
a. process:
If homologs line up askew
And a cross-over occurs A a b B

20. 1. Unequal Crossing-Over a. process: If homologs line up askew
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Unequal Crossing-Over
a. process:
If homologs line up askew
And a cross-over occurs
Unequal pieces of DNA will be exchanged… the A locus has been duplicated on the lower chromosome and deleted from the upper chromosome A a b B

21. 1. Unequal Crossing-Over a. process: b. effects: - can be bad:
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
1. Unequal Crossing-Over
a. process:
b. effects:
- can be bad:
deletions are usually bad – reveal deleterious recessives
additions can be bad – change protein concentration
- can be good:
more of a single protein could be advantageous
(r-RNA genes, melanin genes, etc.)
source of evolutionary novelty (Ohno hypothesis )
where do new genes (new genetic information) come from?

22. Gene A
Duplicated A
generations
Mutation – may even render the protein
non-functional
But this organism is not selected against, relative to others in the population that lack the duplication, because it still has the original, functional, gene.

23. Gene A
Duplicated A
generations
Mutation – may even render the protein
non-functional
Mutation – other mutations may render the protein functional in a new way
So, now we have a genome that can do all the ‘old stuff’ (with the original gene), but it can now do something NEW. Selection may favor these organisms.

24. If so, then we’d expect many different neighboring genes to have similar sequences. And non-functional pseudogenes (duplicates that had been turned off by mutation).
These occur – Gene Families

25. And, if we can measure the rate of mutation in these genes, then we can determine how much time must have elapsed since the duplication event…
Gene family trees…

26. Mechanism #1: Exon Shuffling
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
Mechanism #1: Exon Shuffling
Crossing over WITHIN a gene, in introns, can recombine exons within a gene, producing new alleles.
EXON 1a
EXON 2a
EXON 3a
Allele “a”
EXON 1A
EXON 2A
EXON 3A
Allele “A”
Allele “α”
Allele “ά”

27. 1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
1. Mechanism #1: Exon Shuffling
2. Mechanism #2: Point Mutations
a. addition/deletion: “frameshift” mutations
…T C C G T A C G T ….
Normal
…A G G C A U G C A …
ARG
HIS
ALA
Mutant: A inserted
…T C C A G T A C G T ….
…A G G U C A U G C A …
SER
CYS
DNA
m-RNA
Throws off every 3-base codon from mutation point onward

28. 1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
1. Mechanism #1: Exon Shuffling
2. Mechanism #2: Point Mutations
a. addition/deletion: “frameshift” mutations
b. substitution
… T C C G T A C G T ….
Normal
…A G G C A U G C A …
DNA
m-RNA
ARG
HIS
ALA
Mutant: A for G
…T C C A T A C G T ….
…A G G U A U G C A …
TYR
At most, only changes one AA (and may not change it…)

29. Sources of Variation Causes of Evolutionary Change
VI. Mutation
Overview
Changes in Ploidy
Changes in ‘Aneuploidy’ (changes in chromosome number)
D. Change in Gene Number/Arrangement
E. Change in Gene Structure
F. Summary
Sources of Variation Causes of Evolutionary Change
MUTATION: Natural Selection
-New Genes: 
point mutation  Mutation (polyploidy can make new
exon shuffling  species)
RECOMBINATION:
- New Genes:
crossing over
-New Genotypes:
independent assortment
VARIATION