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79 Cards in this Set
- Front
- Back
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Nondisjunction leads to changes in the number of what?
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Chromosomes!
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What is Nondisjunction?
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A process of failed chromosome and sister chromatid disjunction that can result in changed chromosome #.
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What is a Euploid?
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A # of chromosomes that is an exact multiple of the haploid number. (Ex: 2n, 3n, etc.)
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What is a Aneuploid?
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An uneven number of chromosomes. (Ex: 2n-1 or 2n+1, etc.)
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What is a principal cause of aneuploidy?
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Chromosome nondisjunction!
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Which have more tolerance for changes in chromosome number: animals or plants?
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Plants!
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What is Polyploidy?
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More than two copies of each chromosome
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What is Meiosis I nondisjunction?
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The failure of homologous chromosomes to separate
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What is a trisomic chromosome?
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2n+1, having 3 of one of the chromosomes (versus the normal 2)
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What is a monosomic chromosome?
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2n-1, having just a single copy of one of the chromosomes (versus the normal 2)
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If nondisjunction occurs in meiosis II, does it typically follow a normal or abnormal meiosis I?
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Normal Meiosis I!
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If nondisjunction occurs in Meiosis II, what is the ratio of trisomic, monosomic and normal chromosomes when fertilized with normal gametes??
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25% Trisomic, 25% Monosomic, and 50% Normal
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What is Gene Dosage?
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Gene Dosage is the number of copies of a gene.
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TRUE OR FALSE: Aneuploidy changes the dosage of only a few genes on the affected chromosome.
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FALSE. Aneuploidy changes the dosage of ALL THE GENES on the affected chromosome.
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In a diploid, a normal chromosome has what percentage of gene dosage?
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100%
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In a diploid, a monosomic mutant has just one gene copy and thus what percentage of normal gene dosage?
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50%
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In a diploid, a trisomic mutant has three copies of a gene and thus has what percentage of normal gene dosage?
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150%
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Theoretically, how many different kinds of trisomy in humans are there?
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24! (one for each autosome and one for each X and Y)
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Despite the theoretical number of different trisomy in humans, actual autosomal trisomies occur on what 3 chromosomes?
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13, 18, and 21
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What is the frequency of meiotic nondisjunction in humans?
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15% to 25%
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Haploinsufficiency of what gene appears to play a major role in producing Turner Syndrome?
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SHOX gene
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In a trisomy, what are the two patterns of of homologous chromosome synapsis that are possible among the three chromosomes at metaphase I?
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1. Trivalent synaptic structure
2. Bivalent or univalent synaptic structure |
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Is there a mechanism to divide three chromosomes equally at Anaphase I in a trisomy?
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NO.
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What is Semisterility?
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A reduction, but not complete elimination, of fertility.
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What is Gynandromorphy?
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Sexually ambigous phenotype caused by sex-chromosome mosaicism
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Gynandromorphy develops as a consequence of what?
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MITOTIC nondisjunction early in development
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What is Nullisomy?
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Loss of both homologous pairs, 2n-2
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What is Tetrasomy?
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Gain of a homologous pair, 2n+2
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What is Mosaicism?
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cell of an individual may have different karyotypes
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What is Polyploidy?
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The presence of three or more sets of chromosomes in the nucleus of an organism
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Polyploidy in nature can result from what 2 ways?
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1. Duplication of euploid chromosome sets from single species
2. Combining of chromosome sets from different species |
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What are Autopolyploids?
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A pattern of polyploidy produced by the duplication of chromosomes from a SINGLE SPECIES.
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What are Allopolyploids?
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A polyploid organism arising through the union of chromosome sets from DIFFERENT species.
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What 3 mechanisms lead to autopolyploidy?
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1. Multiple fertilizations
2. Mitotic nondisjunction 3. Meiotic nondisjunction |
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What are the three main consequences of polyploidy in plants?
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1. increase in flower and fruit size
2. Fertility is decreased 3. Increase in heterozygosity relative to diploid |
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What is Hybrid Vigor?
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The greater growth, survival, and fertility of hybrids produced by crossing highly inbred lines
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Certain fruits at the market that are seedless are even or odd numbered polyploidy?
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ODD-numbered polyploidy
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When a chromosome breaks, both strands of DNA are severed at a location called what?
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Chromosome Break Point
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What is Partial Chromosome Deletion?
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The loss of a PORTION of a chromosome due to chromosome breakage
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What is Microdeletion?
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Small deletions that affect one or a few genes
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Microdeletions may behave as recessive mutations if what occurs?
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If the remaining single copies of genes on the homologous unbroken chromosomes are haploinsufficient.
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Microdeletions may behave as dominant mutations if what occurs?
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One or more of the deleted genes is dosage sensitive
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What is a Terminal Deletion?
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The loss of a chromosome segment that includes the telomeric region
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Without a centromere, the acentric fragment lacks what?
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A kinetochore
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Organisms carrying one wild-type chromosome and a homolog with a terminal deletion are called what?
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Partial deletion heterozygotes
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What is an example of a chromosome syndrome caused by terminal deletion?
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Cri-du-chat syndrome
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What is an interstitial deletion?
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The loss of an INTERNAL segment of a chromosome that results from TWO chromosome breaks.
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What is an example of a syndrome caused by an interstitial deletion?
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WAGR syndrome
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An organism carrying one homolog with duplicated material is called what?
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A partial duplication heterozygote
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An organism carrying material deleted from another chromosome is called what?
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A partial deletion heterozygote
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In human chromosomes, duplications and deletions of about how many base pairs are at the lower limit of chromosome banding visualization techniques?
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100,000 to 200,000 base pairs
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Homologous pairs that are mismatched because one contains a large duplication or deletion will form what in synapsis?
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It will form an UNPAIRED LOOP.
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What is the material in the unpaired loop?
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It is normal genetic material if one chromosome carries a deletion and is duplicated genetic material if one homolog carries a duplication.
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What is chromosome inversion?
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Reattachment of broken chromosomes in the wrong orientation
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What is Chromosome Translocation?
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Attachment of broken chromosomes to a nonhomologous chromosome
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Chromosome inversion occurs as a result of what?
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Chromosome breaks followed by reattachment of the free segment in the reverse orientation
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What are the 2 types of chromosome inversion?
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1. Paracentric inversion - single arm: DOES NOT involve centromere
2. Pericentric inversion - INVOLVES the centromere |
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What are Inversion heterozygotes?
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Organisms whose homologous chromosomes have different structural organization.
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In order to bring the homologs of an inversion heterozygote into synaptic alignment during meiosis, what is required to form?
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An inversion loop!
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In inversion heterozygotes, crossing over OUTSIDE the region spanned by the inversion loop takes place in what manner: Normal or abnormal?
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Normal!
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In inversion heterozygotes, crossing over INSIDE the region spanned by the inversion loop results in what?
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Duplications and deletions among the recombinant chromosomes
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What is a dicentric bridge?
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It is a bridge made by two chromosomes that have two centromeres (its what connects the two chromosomes)
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What are the 3 observations about recombination in inversion heterozygotes that have important genetic implications?
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1. Probability of crossover within inversion loop is linked to size of loop
2. Inversion suppresses the production of recombinant chromosomes 3. Fertility may be altered if inversion heterozygote carries a VERY large inversion |
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In inversion heterozygotes, a larger inversion loop corresponds to what in terms of crossing over?
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Higher probability in crossing over!
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What are the 3 types of translocation?
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1. Unbalanced translocation
2. Reciprocal balanced translocation 3. Robertsonian Translocation |
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What is unbalanced translocation?
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Reattachment to a nonhomologous chromosome in a one-way event (one piece is translocated to a NONHOMOLOGOUS chromosome, unevenly)
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How is Reciprocal Balanced Translocation produced?
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Produced when breaks occur on two NONHOMOLOGOUS chromosomes and the resulting fragments switch places (equally).
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What is Robertsonian Translocation?
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The fusion of two NONHOMOLOGOUS chromosomes (can sometimes cause trisomy 21)
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What are Trasposable Genetic Elements?
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DNA sequences of various lengths and composition that evolved the ability to move within the genome by enzyme driven process: transposition.
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How do Transposable elements create mutations?
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Insertion into wild-type alleles
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What is Insertional Inactivation?
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Insertion of a transposable genetic element into what was formerly the wild-type allele causing inactivation of mutant allele and blocks production of starch branching allele.
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Evolutionarily, transposable elements can do what to the genome size: increase it or decrease it?
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INCREASE it!
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What is a Replicative Transposable Element?
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transposon is copied and new copy inserted in the genome
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What is an Excising Transposable Element?
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transposon is removed using transposase and then reinserts in another part of the genome
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What is Transposition?
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Process that moves transposable genetic elements in genomes and was first discovered in maize
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What is Transposase?
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Enzyme responsible for transposition and is encoded by many transposable genetic elements
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How does transposition produce mutations?
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Through insertional inactivation!
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What transposable elements encode transposase to drive their movement?
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Autonomous transposable elements
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What transposable elements must rely on other transposable elements for transposase production?
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Non-automous elements
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