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…

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

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.

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:

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.

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.

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

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

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.

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

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?

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’)

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

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.

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)

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”

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)

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

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

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

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 - 1970) where do new genes (new genetic information) come from?

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.

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.

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

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…

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”

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

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…)

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