Objectives for Exam 2 PCB 3063 Fall 2012 DR BATES Chromosome Abnormalities Chapter 6 Q Know the following terms and their significance Chromosome mutations or chromosome abnormalities change in total of chromosomes the deletion or duplication of genes or segments of a chromosome and rearrangements of the genetic material either within or among chromosomes PASSED TO OFF SPRING Nondisjunction leads to monosomy and trisomy where paired homologs fail to separate during segregation ABNORMAL DISTRIBUTION OF CHROMOSOMES Aneuploidy general condition where an organism loses or gains one or more chromosomes but not a complete set 2n or X chromosome s Monosomy loss of one chromosome monosomy for the X chromosome occurs in humans monosomy for any of the autosomes is usually not viable 2n 1 ex Turner syndrome 45 X Trisomy addition of an extra chromosome produces more viable individuals in animal and plant species than does the loss of a chromosome 2n 1 Down Syndrome trisomy 21 the only human trisomy autosomal in which a significant number of individuals can survive longer than a year The frequency of Down syndrome is related to the mothers age Amniocentesis chorionic villus sampling fetal cells are obtained from the amniotic fluid or the chorion of the placenta after the cells are obtained the karyotype can be determined Triploid three sets of chromosomes are present 3n Tetraploid four sets of chromosomes present 4n Polyploid multiple chromosome sets Rare in humans but occurs in amphibians and lower animals Chromosome deletion chromosome or sequence of DNA is missing Duplication when any part of the genetic material a single locus or a large piece of a chromosome is present more than once in the genome Inversions rearrangement in where a segment of a chromosome is reversed end to end 180 degrees Results in a loss of genetic material but simply rearranges the linear gene sequence Translocations Rearrangement of parts between non homologous chromosomes Q Important Concepts Understand how nondisjunction in meiosis leads to monosomy and trisomy and be able to explain why essentially the only monosomies and trisomies observed in humans involve chromosomes X Y and 21 Know that Klinefelter syndrome is more frequent than Turner syndrome and why Nondisjunction during the first and second meiotic divisions some of the gametes that are formed either contain two members of a specific chromosome or lack that chromosome After fertilization by a gamete with a normal haploid content monosomic disomic normal or trisomic zygotes are produced The only monosomies observed in humans involve X and Y chromosomes because any monosomies involving autosomes are lethal The other trisomies and monosomies are usually not viable in humans Q Know that changes in chromosome structure can arise due to abnormal pairing and crossing over in meiosis or to errors during DNA replication These structural changes include insertions duplications deletions and translocations Changes in chromosome structure can occur through unequal crossing during meiosis Q Be able to explain the role of polyploidy in the formation of new species Polyploidy originates in 2 ways 1 Addition of one or more extra sets of chromosomes identical to normal haploid complement of the same species resulting in autopolyploidy 2 Or the combination of chromosome sets from different species occurring as a consequence of hybridization formation of new species Distinction is based on the genetic origin of the extra chromosome sets Q Understand the inheritance of Familial Downs Syndrome and understand why the presence of a translocation can result in increased frequencies of miscarriages Familial Downs Syndrome due to a human translocation most down s syndrome is due to trisomy 21 due to nondisjunction but this is an inherited translocation carrier has 45 chromosomes and exhibits the normal phenotypes doesn t contain the complete diploid amount of genetic material Quantitative Genetics Polygenic Inheritance Chapter 22 Q Important Terms concepts to know Polygenic inheritance also known as quantitative inheritance refers to inheritance of a phenotypic characteristic trait that is attributable to two or more genes or the interaction with the environment or both Unlike monogenic traits polygenic traits do not follow patterns of Medel s inheritance separated traits Instead their phenotypes typically vary along a continuous gradient depicted by a bell curve Trait is determined by 3 gene pairs which contribute additively to the phenotype ex height eye color skin color blood pressure IQ behavioral traits bell each pair has an additive and a non additive allele phenotype reflects the total number of additive alleles Discontinuous Traits individuals can be grouped into distinct phenotypes Continuous traits individuals display a continuous range of phenotypes shaped distribution Multifactorial traits polygenic traits that are influenced by the environment Quantitative traits Additive and nonadditive alleles Complicated of simple Twin studies Concordance When a pair of twins display the same phenotype Monozygotic twins should be 100 concordant Dizygotic twins less than 100 concordant You should understand the genetic basis for traits that display continuous variation polygenic inheritance involving additive or nonadditive alleles and have a general understanding of the types of traits that have this genetic basis You should be able to do simple problems that require determining the number of genes that control a polygenic trait and the amount each allele contributes to the phenotype similar to those in homework 3 Q You should also be able to analyze human twin study data and identify traits that are determined primarily by the environment primarily by genes or by a mixture of both genes and environment Many polygenic traits are also influenced by the environment multifactorial traits additive alleles Polygenic traits may be more complicated that simple additive and non When a pair of twins display the same phenotype Concordant If the trait is controlled completely by genes monozygotic twins should be 100 concordant and Dizygotic twins should be 100 concordant Can use this basis to determine if a trait is entirely environmental or gene controlled Linkage and Mapping Chapter 7 Q Important Terms concepts to know Linkage genes that are part of the same chromosome and thus can t undergo independent assortment Genes on the same chromosome are said to be linked Linkage is usually
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