BIO 305 1st Edition Lecture 10 Outline of Last Lecture I. Aneuploidy, Euploidy, and other Examples of Chromosome NumberII. Variation in the Structure and Arrangement of ChromosomesIII. DiseasesIV. Sample QuestionsOutline of Current Lecture I. Variation in the Structure and Arrangement of Chromosomes (continued)II. The Inheritance of Fragile X SyndromeIII. More diseasesIV. Vocabulary and Sample QuestionsCurrent LectureI. Variation in the Structure and Arrangement of Chromosomes (continued)Translocation: segment changes position but there is no net gain or loss of genetic material(4 Types):intrachromosomal translocation – the DNA segment stays within the same chromosomevs.Interchromosomal translocation - between non-homologous chromosomesReciprocal translocation – the most frequent and important type of translocation in which two segments switch place between two non-homologous chromosomesRobertsonian translocation – most common type of chromosomal rearrangement for humansBreakage occurs in the centromere occurs in two different chromosomes, and two pieces fuse (centric fusion) while the acentric fragments are lostTranslocations are harmful even if there no net change in genetic material amount, because there is still disturbance gene location, which can lead to phenotypic issuesEspecially in oncogenes, which if tampered with, could lead to cancerMeiosis is a problem in heterozygotes:Homologues create a cruciform arrangement in metaphase – error results when there is a deficiency in the blue part and extra orange or when there is extra orange and blue deficiency II. The Inheritance of Fragile X SyndromeKey features of inheritance:1) among sons of carrier females (females heterozygous for fragile X), 20% are normal.These sons are “normal transmitting males” because they can transmit the Fragile X on to daughters.Thus the sons of those daughters also often show the syndrome.2) Daughters of carrier females have smaller chance (%50) of inheriting Fragile X, but 30% show mild effects on mental health3) “Anticipation” - Chances of carriers producing affected offspring (especially male offspring) increases and so does severity Molecular Explanation:People who are carriers or have Fragile X can have 50+ times more CGG repeats in the FMR-1 gene than normal, and these repeats amplify over generations and produce the syndrome- Mothers receiving these multiplied repeats undergo meiosis and the “triplet repeat” may expand to produce a full mutation- This does not occur in male meiosisIn a pedigree, ancestor males and females may be half-shaded to indicate that they carry premutations and the descendant sons will very frequently be full-shaded as a result (aka they carry the Fragile X disease)III. More DiseasesChronic Myelogenous Leukemia – caused by a translocation between chromosomes 9 and 22, which creates a “Philadelphia chromosome”.Burkitt’s Lymphoma – cancer caused by a translocation between 8 and 14Fragile X Syndrome – in mentally retarded males, the X chromosome is broken at a particular site (Fragile X site at the FMR-1 gene) under conditions lacking in folic acid- Note: This disease shows that there are genes on the X chromosome that affect mental development- Note: The likelihood of developing this syndrome increases with the mother’s age (the mother loses production of folic acid over time)- Note: This is the second most common mental retardation disease behind Down SyndromeFamilial Down Syndrome – chromosome 21; realized that down syndrome tends to occur frequently in a family. This is because if someone is a translocation carrier and mates with a normal person, the possible gametes that could occur: only a ¼ chance that child will be normalMyotonic dystrophy – a human disorder due to triplet repeatsHuntington’s disease – another human disorver due to triplet repeatsIV. Vocabulary and Sample QuestionsTranslocation – a chromosomal mutation in which a segment of a chromosome changes positionOncogene – genes that are involved in regulation of cell divisionPositional effect – when the phenotype seen depends on not just the allele of a particular gene, but also the position of the gene in a particular chromosomeFISH – fluorescently detects for a particular gene, can use it to see cruciform and translocationsPremutation – Symptomless individuals who have an intermediate number of copiesFull mutation – when the permutation is passed on and this is expanded in meiosis to show the phenotype in the progenySample Questions1. A hybrid allotetraploid species (2n = 60) was backcrossed to one of the suspected parents (2n = 30). When the F1 underwent meiosis, the prophase chromosome configuration was examined. If the guess about the suspected parent were correct, what would the chromosome configuration look like? A) 30 pairs B) 45 singles C) 60 singles D) 15 pairs and 15 singles E) 30 pairs and 15 singles2. In a triploid of genotype B/b/b, what proportion of gametes will be (genotypically) B?A) 1/6B) 1/4C) 1/3D) 1/2E) 2/33. A man is found to be karyotypically 47,XYY. The presence of an extra Y chromosome most likely results from:A) non-disjunction in a maternal meiocyte at meiosis I.B) non-disjunction in a maternal meiocyte at meiosis II.C) non-disjunction in a paternal meiocyte at meiosis I.D) non-disjunction in a paternal meiocyte at meiosis II.E) unequal crossing over.4. Which statement about chromosomal mutations is INCORRECT? a) Polyploids often have bigger cells than diploids.b) The hybrid between cabbage (2n=18) and radish (2n=18) has 18 chromosomes and is sterile. c) Triploid watermelon is generally seedless, due to the problem of chromosomal segregation in meiosis.d) The domestic wheat is an allopolyploid. e) Monosomy is lethal in humans.5. Which statement about chromosomal mutations is INCORRECT? a) Heterozygotes of interchromosomal reciprocal translocation usually show normal phenotypes, but may have reduced fertility. b) Large deletions have similar phenotypic effects as partial monosomy. c) Recombination rate is reduced in inversion loops due to the difficulty of synapsis of homologous chromosomes during meiosis.d) Robertsonian translocation must involve more than one chromosome. e) Robertsonian translocation may cause Down syndrome in the next generation.ANSWERS:1. D, each parent donates it’s haploid number to fertilize and undergo meiosis (30 from one and 15 from the other) 15 of those haploid were able to pair and