BIO 305 1st Edition Lecture 9 Outline of Last Lecture I. Extra nuclear InheritanceII. Chloroplast vs. Mitochondrial Genome and InheritanceIII. Other Forms of Non-Mendelian InheritanceA. Three Examples: Neurospora, S. Cerevisae, and HumansB. Mitochondrial DNA MutationsC. Maternal Effect and Shell CoilingOutline of Current Lecture I. Aneuploidy, Euploidy, and other Examples of Chromosome NumberII. Variation in the Structure and Arrangement of ChromosomesIII. DiseasesIV. Sample QuestionsCurrent LectureI. Aneuploidy, Euploidy, and other Examples of Chromosome NumberUnderstanding the difference between Aneuploidy and Euploidy:Aneuploidy – 2n minus or plus x, there is a difference in number of chromosomes from the normal (ex: monosomy (2n-1), trisomy (2n+1), tetrasomy, etc…)Euploidy – multiples of n, a difference depending on the species of organism(ex: diploidy (2n), polyploidy (more than 2n), triploidy (3n), tetraploidy, etc…)Autopolyploidy – multiples of the same genomeAllopolyploidy – multiples of different genomesIn what ways can chromosome number be affected?Recall: Non-disjunction Diseases (Ex: Klinefelter, Turner syndrome, sex chromosomes)Monosomy in autosomes in humans: lethal, in plants: more toleratedResults in: 1) Unmasking of recessive deleterious mutations tolerated in heterozygotes 2) Unbalanced gene expression, which affects developmentTrisomy in humans: some bad phenotypic effects, in plants: altered phenotypeExample of aneuploidy in plants: Capsule shape of fruits in the Jimson weed vary depending on how many extra chromosomes (2n+C#)Example of aneuploidy in humans: Down Syndrome – Trisomy in the 21st chromosome, due to nondisjunction in meiosis I in oogenesisNote: as age of the mother increases, so does the likelihood of Down SyndromeIn abnormal conceptions, aneuploids can result in either live births or abortions, but chromosomal rearrangements result in livebirths while polyploids most often result in spontaneous abortionsHow does Autopolyploidy occur?1) Failure of all chromosomes to segregate during meiotic divisions (I or II)2) Two sperm fertilize one egg3) Artificial cross of a diploid and a tetraploid Why are odd-numbered polyploids less common in nature than even-numbered?Odd-chromosomes produce unbalanced (aneuploid) gametes and lead to sterilityA triploid (3n) gamete can be split into a trivalent in one cell and bivalent + univalent in another cell. Even-numbered polyploids can also result in sterile gametes Ex: Colchicine – induces formation of polyploids by interfering with spindle formation in mitosis (in other words it prevents mitotic division, thus creating one tetraploid cell instead of two diploid cells) Polyploidy also increases cell size (volume), which results in larger tissues:Commercial advantages: larger fruit, triploid seedless banana and watermelon, etc. Allopolyploidy – having two or more complete sets of chromosomes derived from different species (in the crossing of cabbage and radish: two different genomes were doubled again)Endopolyploidy – only certain cells of an otherwise diploid organism are polyploidy. It is the result of endomitosisAmphidiploids are usually fertile and have increased size plus chance of favorable combination of characteristics of each species:Ex: The crossing of a 2n = 18 cabbage with a 4n = 36 radish resulted in a sterile hybridII. Variation in the structure and arrangement of chromosomesThere are five types of chromosomal alterations:Deletion – riddance of a gene  “partial monosomy”Three types of deletion:1) Terminal deletion – the end of a chromosome breaks off2) Origin of intercalary deletion – chromosome makes a loop and loop is lost3) Formation of deficiency loop – in synapsis, part of chromosome is pinched offPseudodominance – when the recessive allele gives its expression in the absence of a dominant allele Duplication – a segment of chromosome is doubledEx: Bar mutants of Drosophila – different numbers of copies in the 16A region of the X chromosome (wild-type females have one copy on each x chromosome)homozygous Bar mutants sometimes produce progeny with even smaller eyes, called double-Bar, this is due to having 3 copies of the region on each XHow do these duplications occur?“unequal crossing over”, 3 rules:1) A single unequal crossover = 1 duplication and 1 deletion2) An unequal crossover within duplicated regions = greater duplication3) As # of duplicate copies increases = unequal crossover likelihood increasesimplication: once the process has started there is a tendency over evolutionary time for the number of copies to increase - crucial genes are not free to change much (not happy for new functions)- if a new copy is produced by unequal crossing-over, the extra copy can evolve over time. Eventually perhaps producing a protein with very different functionsEx: Globin genes – produces alpha and beta globin chains which comprise hemoglobinThe process of copies producing new proteins can result in families of related genes that make similar proteinsEx: Duplication = generation of arrays of genes whose products are in large demands- examples – rRNA genes, histone genesInversion – when a segment of a chromosome is reoriented 180 degrees from normal- requires breaks in the chromosome- Paracentric inversion: when the two breaks occur beside the centromere, thus arm ratio remains unchanged- Pericentric inversion: when the two breaks occur with the centromere between, thus arm ratio changes No genetic material is gained or lost, thus even if homozygous or heterozygous: no phenotypic effectException: In heterozygotes, reproductive consequences can occur as a result of problems with pairing and alignment of homologs in meiosis This does not cause problems unless crossing over occurs within the inverted region!Results of paracentric heterozygote inversions  dicentric and acentric chromosomesResults of pericentric heterozygote inversions  duplications and deletioncrossover suppression – because the only viable offspring are those that result from gametes who did not have crossovers within the inverted region, it appears that crossing over in the inversion has been suppressedDoes crossover happen in this region?Yes, we just can’t observe the result in the progeny. The genetic result is verytight linkage of genes in an inverted segmentWhy is reduced recombination important in the evolutions of the some organisms but not others?A species may evolve