Understanding Mutations: Ploidy Changes and Genetic Consequences

1. 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. 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 • 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. Failure of Meiosis I 2n = 4 Gametes: 2n = 4

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. Failure of Meiosis II 2n = 4 Normal gamete formation is on the bottom, with 1n=2 gametes. The error occurred up top, with both sister chromatids of both chromosomes going to one pole, creating a gametes that is 2n = 4.

6. 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.

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 • 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.

8. 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

9. 2n 1) Consider a bud cell in the flower bud of a plant.

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.

11. 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

12. 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 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?

13. 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’)

14. 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… 2n 2n 4n 1n 1n 2n 3n 4n 2n Zygote Zygote Triploid is a dead-end… so species are separate Gametes Gametes

15. 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.

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)

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 • a. trisomies • Trisomy 21 – “Downs’ Syndrome”

18. 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” • Trisomy 18 – Edward’s Syndrome • Trisomy 13 – Patau Syndrome • Trisomy 9 • Trisomy 8 • Trisomy 22 • Trisomy 16 – most common – 1% of pregnancies – always aborted Some survive to birth

19. 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 • 47, XXY – “Klinefelter’s Syndrome” Extreme effects listed below; most show a phenotype within the typical range for XY males

20. 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 • 47, XXX – “Triple-X Syndrome” No dramatic effects on the phenotype; may be taller. In XX females, one X shuts down anyway, in each cell (Barr body). In triple-X females, 2 X’s shut down.

21. 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 • 47, XYY – “Super-Y Syndrome” Often taller, with scarring acne, but within the phenotypic range for XY males

22. 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)