Sources of Variation Mutation Recombination VII Mutations I

Sources of Variation: Mutation Recombination

VII. Mutations I: Changes in Chromosome Number and Structure - Overview:

VII. Mutations I: Changes in Chromosome Number and Structure - Overview: 1) A mutation is ….

VII. Mutations I: Changes in Chromosome Number and Structure - Overview: 1) A mutation is a change in the genome of a cell.

VII. Mutations I: Changes in Chromosome Number and Structure - Overview: 1) A mutation is a change in the genome of a cell. 2) Evolutionarily important mutations are heritable (not somatic). However, the tendency for a gene to mutate in somatic tissue (cancer) as a result of sensitivity to env conditions may be heritable.

VII. Mutations I: Changes in Chromosome Number and Structure - Overview: 3) Changes occur at 4 scales (large to small) - Change in the number of SETS of chromosomes (change in PLOIDY) - Change in the number of chromosomes in a set (ANEUPLOIDY: trisomy, monosomy) - Change in the number/arrangement of genes on a chromosome - Change in the nitrogenous base sequence within a gene In general, the LARGER the change, the more dramatic (and usually deleterious) the effects. If you have a functioning genome, a big change is going to be MORE LIKELY to disable it than a small change…

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms:

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: a. Autopolyploidy: production of a diploid gamete used in reproduction within a species. Failure of meiosis I or II 2 n gamete 3 n zygote Correct meiosis in other parent 1 n gamete

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: a. Autopolyploidy: production of a diploid gamete used in reproduction within a species. Errors in mitosis can also contribute, in hermaphroditic species

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

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

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

2 n 1) Consider a bud cell in the flower bud of a plant. 4 n 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 2 n SPERM and 2 n EGG 4) If it is self-compatible, it can mate with itself, producing 4 n zygotes that develop into a new 4 n 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… 2 n 4 n 4 n 1 n 2 n 2 n 3 n Zygote 1 n 2 n Gametes Triploid is a dead-end… so species are separate Zygote Gametes

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: a. Autopolyploidy: production of a diploid gamete used in reproduction within a species. b. Allopolyploidy: fusion of gametes from different species (hybridization). These are usually sterile because the chromosomes are not homologous and can’t pair during gamete formation. BUT… if the chromosomes replicate and separate without cytokinesis, they create their own homologs and sexual reproduction is then possible.

Spartina alterniflora from NA colonized Europe X Spartina maritima native to Europe Sterile hybrid – Spartina x townsendii Allopolyploidy – 1890’s Spartina anglica – an allopolyploid and a worldwide invasive outcompeting native species

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: Polyploidy is common in plants; 50% of angiosperm species may be the product of polyploid speciation events.

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: Polyploidy is common in plants; 50% of angiosperm species may be the product of polyploid speciation events. In vertebrates, polyploidy decreases in frequency from fish to amphibians to reptiles, and is undocumented in birds. There is one tetraploid mammal. (Red viscacha rat).

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism:

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism: - when the sexes are separate, the rare, random mutation of producing a diploid gamete is UNLIKELY to occur in two parents simultaneously. So, the rare diploid gamete made by one parent (karyokinesis without cytokinesis doubling chromosome number in a cell) will probably fertilize a normal haploid gamete. This produces a TRIPLOID… which may live, but would be incapable of sexual reproduction. 2 n 1 n 3 n

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism: - unless…. the new organism could ALSO produce eggs without reduction. . clonally… and these are the rare animals that we see – triploid ‘species’ that are composed of females that reproduce asexually. (Some may still mate with their diploid ‘sibling’ species so that the sperm stimulated the egg to develop – but without incorporation of sperm DNA. ) Like this Blue-spotted Salamander A. laterale, which has a triploid sister species, A. tremblayi

C. Inornatus C. neomexicanus C. tigris Parthenogenetic diploid

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism: - So, in species with separate sexes, polyploidy is probably rare because the typical condition would be TRIPLOIDY, which is usually a sterile condition.

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism: - So, in species with separate sexes, polyploidy is probably rare because the typical condition would be TRIPLOIDY, which is usually a sterile condition. - But in hermaphroditic organisms (like many plants), a single mutation can affect BOTH male and female gametes.

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism: SO! Polyploidy may be more frequent in plants because they are hermaphroditic more often than animals; especially vertebrates. Most cases of polyploidy in animals is usually where triploid females survive and reproduce asexually. Also, simpler development in plants means they may tolerate imbalances better.

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy 1. Mechanisms: 2. Frequency: 3. The effect of hermaphrodism: 4. Evolutionary Importance: - obviously can be an instant speciation event - polyploidy is also a mechanism for “genome doubling” or “whole genome duplication” - this duplication allows for divergence of copied gene function and evolutionary innovation. Eventually, the copies may be so different that they don’t really represent duplicates any more… resulting in “diploidization”.

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy B. Aneuploidy

B. Aneuploidy 1. Mechanism: Non-disjunction during gamete formation During either Meiosis I or II, segregation of (homologs or sister chromatids) does not occur; both entities are pulled to the same pole.

B. Aneuploidy 1. Mechanism: Non-disjunction during gamete formation During either Meiosis I or II, segregation of (homologs or sister chromatids) does not occur; both entities are pulled to the same pole. This produces gametes with one more (1 n + 1) or one less (1 n -1) chromosome than they should have. Subsequent fertilization with a normal haploid (1 n) gamete produces a trisomy (2 n+1) or monosomy (2 n-1).

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy B. Aneuploidy C. Changes in Gene Number and Arrangement

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy B. Aneuploidy C. Changes in Gene Number and Arrangement 1. Deletions and Additions:

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy B. Aneuploidy C. Changes in Gene Number and Arrangement 1. Deletions and Additions: a. mechanisms: i. unequal crossing over:

i. Unequal Crossing-Over a. process: If homologs line up askew: A B a b

i. Unequal Crossing-Over a. process: If homologs line up askew And a cross-over occurs A B a b

i. 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 B A a b

i. Unequal Crossing-Over a. process: b. effects: - can be bad: deletions are usually bad – reveal deleterious recessives additions can be bad – change protein concentration

i. Unequal Crossing-Over a. process: b. effects: - can be bad: - can be good: deletions are usually bad – reveal deleterious recessives additions can be bad – change protein concentration more of a single protein could be advantageous (r-RNA genes, melanin genes, etc. )

i. Unequal Crossing-Over a. process: b. effects: - can be bad: - can be good: deletions are usually bad – reveal deleterious recessives additions can be bad – change protein concentration 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…

VII. Mutations I: Changes in Chromosome Number and Structure A. Polyploidy B. Aneuploidy C. Changes in Gene Number and Arrangement 1. Deletions and Additions: a. mechanisms: i. unequal crossing over: (both) ii. Intercalary Deletion A B C

1. Deletions and Additions: a. mechanisms: i. unequal crossing over: (both) ii. Intercalary Deletion B A C

1. Deletions and Additions: a. mechanisms: i. unequal crossing over: (both) ii. Intercalary Deletion A C

1. Deletions and Additions: a. mechanisms: i. unequal crossing over: (both) ii. Intercalary Deletion synapsis: -recognized by the formation of a ‘deletion loop’ in homolog during

1. Deletions and Additions: a. mechanisms: i. unequal crossing over: (both) ii. Intercalary Deletion iii. Transposons (addition) - transposons are copied (replicated) independent of the S phase of interphase…the copy is inserted elsewhere in the genome. Create homologus regions that lead to unequal crossing over and duplications

1. Deletions and Additions: a. mechanisms: i. unequal crossing over: (both) ii. Intercalary Deletion iii. Transposons (addition) - OR, a transposon can be inserted within a gene, destroying it and functionally ‘deleting’ it.

VI. Mutation A. Overview B. Changes in Ploidy C. Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome)

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome)

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome) Chromosomes are no longer homologous along entire length B-C-D on top d-c-b on bottom

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome) Chromosomes are no longer homologous along entire length ONE “loops” to get genes across from each other… And if a crossover occurs….

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome) The cross-over products are nonfunctional, with deletions AND duplications

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome) The only functional gametes are those that DID NOT cross over – and preserve the parental combination of alleles

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome) Net effect: stabilizes sets of genes. This allows selection to work on groups of alleles… those that work well TOGETHER are selected for and can be inherited as a ‘coadapted gene complex’

VII. Mutation A. Changes in Ploidy B Changes in ‘Aneuploidy’ (changes in chromosome number) C. Change in Gene Number/Arrangement 1. Deletions and Additions 2. Inversion (changes the order of genes on a chromosome) 3. Translocation

Translocation Downs. Transfer of a 21 chromosome to a 14 chromosome Can produce normal, carrier, and Down’s child.