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Questions and Answers
What is the definition of aneuploidy?
Which condition is characterized by the presence of an extra X chromosome in males?
What type of chromosomal mutation causes non-disjunction during cell division?
Which of the following describes Klinefelter Syndrome?
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What is the chromosomal configuration associated with Turner Syndrome?
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Which of the following represents a form of polyploidy?
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What are the physical characteristics typically associated with Klinefelter Syndrome?
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Which syndrome is linked with the 47, XYY condition and is sometimes referred to as Crime Syndrome?
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What is the chromosomal composition associated with Metafemale syndrome?
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Which of the following is a common symptom of Cri-du-chat syndrome?
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What is the estimated occurrence rate of Down syndrome?
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What is the primary effect of colchicine on cell division?
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What causes the formation of autopolyploids?
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What chromosome set does an allotetraploid organism have?
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Which condition describes the genetic disorder characterized by a deletion on chromosome 5?
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Which of these is NOT a characteristic feature of Metafemale syndrome?
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Which of the following is classified as an economically important triploid plant?
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What type of deletion occurs near the end of a chromosome?
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What is the primary benefit of producing autopolyploids in agriculture?
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Which method is used to induce the formation of tetraploids from diploids in experiments?
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What is a potential result of hybridization between closely related species?
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Which phenomenon is described as having a part of genetic material present more than once in the genome?
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What role do ribosomal RNA genes play in organisms?
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Which of the following combos outlines the significance of phenotypic variation in organisms?
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What is the main consequence of individuals being heterozygous for an inversion?
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What characterizes a balanced translocation?
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How are common fragile sites different from rare fragile sites?
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What is the range of trinucleotide repeats that is considered normal for fragile X syndrome?
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Which type of chromosomal abnormality typically leads to higher chances of miscarriage in affected couples?
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Which syndrome is most commonly associated with fragile sites on chromosomes?
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What is genetic anticipation in the context of fragile X syndrome?
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Which gene is responsible for the fragile X syndrome?
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What is a significant feature of common fragile sites in the human genome?
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What percentage of males with Fragile X Syndrome are typically mentally retarded?
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What happens to the FHIT gene in individuals with lung cancer?
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Which condition can result from an increased number of trinucleotide repeats beyond 200?
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Which type of chromosomal feature is characterized by heritable points that may break under replication stress?
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Study Notes
Chromosome Mutations
- Chromosome mutations are disruptions in the normal chromosomal content of a cell.
- A major cause of genetic conditions in humans, such as Down syndrome.
- Includes changes in the total number of chromosomes, deletion or duplication of genes or segments of a chromosome, and rearrangements of genetic material.
- Variations in chromosome numbers include aneuploidy and polyploidy.
Aneuploidy
- An organism gains or loses one or more chromosomes, but not a complete set.
- Types include:
- Monosomy: 2n - 1
- Trisomy: 2n + 1
- Tetrasomy: 2n + 2
- Pentasomy: 2n + 3
Polyploidy
- More than two multiples of the haploid chromosome set are found.
- Types include:
- Triploid: 3n chromosomes
- Tetraploid: 4n chromosomes
- Pentaploid: 5n chromosomes
Non-disjunction
- The failure of homologous chromosomes to separate during anaphase.
- Can produce eggs with two X chromosomes or none instead of one.
Sex Chromosomes Aberrations
Klinefelter Syndrome
- "XXY Males" or "47, XXY Males"
- The most common sex chromosome disorder.
- Occurs in 2 out of every 1,000 males.
- Individuals are sterile, have longer arms and legs, and are taller than their peers.
- Characterized by microorchidism (small testicles), hypogonadism (decreased testicular hormone), gynecomastia (breast enlargement), rounded hips, and below-normal IQ.
- Higher incidence of speech delay and dyslexia.
Turner Syndrome
- 45, X0 condition.
- Occurs in 1 in 2,000 female births.
Jacob Syndrome
- 47, XYY condition.
- Individuals are above average height (over 6 ft tall) and have subnormal intelligence.
- Controversial - Criminal Syndrome: Although many males do not exhibit antisocial behavior and lead normal lives, there is a high incidence of correlation between the extra Y chromosome and a predisposition to behavioral problems.
Metafemale Syndrome
- 47, XXX condition
- Occurs in 1 in 1,200 female births.
- Individuals have underdeveloped secondary sex characteristics, menstrual irregularities, and early onset of menopause.
- There's a tendency towards learning disabilities.
Autosome Aberrations
Cri-du-chat Syndrome
- "Chromosome 5p deletion syndrome", "5p minus syndrome" or "Lejeune’s syndrome"
- 46,5p- condition.
- A French term meaning "cat-cry or call of the cat" referring to the characteristic cry of affected children.
- Genetic disorder due to a missing part of chromosome 5 (segmental deletion).
- Occurs in 1 in 20,000 to 1 in 50,000 births.
- The chromosome carrying the deletion is often inherited from the father.
- Signs and symptoms include small size at birth, respiratory problems, an unusual cat-like cry due to larynx development issues, microcephaly (small head), an unusually round face, a small chin, widely set eyes, folds of skin over the eyes, a small bridge of the nose, heart defects, muscular or skeletal problems, and hearing or sight problems.
Down Syndrome
- Trisomy 21
- 47,21+
- Discovered in 1866 by Langdon Down.
- Occurs in 1 in every 800 births.
Polyploidy
- The addition of one or more extra sets of chromosomes, identical to the normal haploid complement of the same species (Autopolyploidy).
- The combination of chromosome sets from different species (Allopolyploidy).
Autopolyploidy
- Additional set of chromosomes are identical to the parent species.
- Causes:
- Failure of all chromosomes to segregate during meiotic division.
- Autotriploids - 3n chromosomes
- Autotetraploids - 4n chromosomes.
Value of Autopolyploidy
- Commercial Value:
- Plants - Horticultural value: increased size of fruits and flowers.
- Autopolyploids are larger than their diploid relatives (larger in cell size, not in cell number).
- Experiment:
- Tetraploids can be produced from diploids by applying cold or heat shock to meiotic cells or by applying colchicine to somatic cells undergoing mitosis.
- Colchicine: an alkaloid that interferes with spindle formation, preventing replicated chromosomes from separating during anaphase.
- Economically Important Triploid Plants: potato, bananas, seedless watermelons, apples, and strawberries.
Allopolyploidy
- Hybridization of two closely related species.
- Hybrid species resulting chromosome sets may be sterile due to the inability to produce viable gametes.
- Allotetraploid or Amphidiploid: Diploid for two genomes derived from different species.
Amphidiploid
- Potential to form balanced gametes, making them reproductively successful.
- Amphidiploid plants:
- Cabbage and raddish (unsuccessful)
- Wheat and rye (grass family): wheat with high yield and rye with growth tolerance in unfavorable environments.
Variation in Chromosome Structure and Arrangement
Deletion
- A chromosome breaks in one or more places and a portion is lost.
- Types:
- Terminal deletion: near the end of the chromosome.
- Intercalary deletion: interior of the chromosome.
Duplication
- Any part of the genetic material, a single locus or a large piece of chromosome, is present more than once in the genome.
Significance of Duplication
- Gene Redundancy: Ribosomal RNA genes support protein synthesis and development after fertilization.
- Phenotypic Variation: Exhibited in Bar-eyed fruit flies.
- Important source of genetic variability during evolution.
Inversion
- A segment of a chromosome is turned around 180 degrees within the chromosome.
- Does not involve a loss of genetic information but simply rearranges the linear gene sequence.
- Usually does not cause abnormalities in carriers as long as the rearrangement is balanced.
- Individuals heterozygous for an inversion may have an increased production of abnormal chromatids, leading to lowered fertility due to unbalanced gametes.
- The most common inversion in humans is on chromosome 9, at inv(9)(p11q12), increasing the risk of miscarriage for about 30% of affected couples.
Translocation
- The movement of a chromosomal segment to a new location in the genome.
- Balanced translocation: pieces of chromosomes are rearranged, but no genetic material is gained or lost.
- Unbalanced translocation occurs when a child inherits a chromosome with extra or missing genetic material from a parent with a balanced translocation.
Chromosomal Fragile Sites
- Specific heritable points on a chromosome that tend to form a gap or constriction and may tend to break when the cell is exposed to partial replication stress.
- Over 120 fragile sites have been identified in the human genome.
Types of Fragile Sites
- Common: Part of normal chromosome structure, present in all or nearly all individuals.
- Rare: Found in less than 5% of the population, often composed of two- or three-nucleotide repeats.
Common Fragile Sites
- Not especially prone to spontaneous breaks under normal conditions.
- Of interest in cancer studies because they are frequently affected in cancer and can be found in healthy individuals.
Rare Fragile Sites
- Susceptible to spontaneous breakage during replication, often affecting neighboring genes.
FRAXA: Fragile X Syndrome or Martin-Bell Syndrome
- Most common cause of hereditary mental retardation.
- Occurs in 1 in 1,250 males, 1 in 2,500 females.
- A dominant trait.
- Male expression rate is higher than females (80% vs. 30%).
- Phenotypes: mentally retarded, long narrow faces, protruding chins, enlarged ears, and increased testicular size.
FMR-1 Gene
- Responsible for FRAXA syndrome.
- Trinucleotide repeat: a phenomenon that repeats a cluster of three nucleotides, expanding gene size and resulting in a disease phenotype.
- Number of repeats correlates with the expression of fragile X syndrome:
- 6-54 repeats: Normal
- 55-200 repeats: "Carriers" of the disorder.
-
200 repeats: Express the syndrome.
Genetic Anticipation
- A phenomenon showing a continuous increase in the number of repeats in future generations until a threshold is reached (200 repeats), leading to the expression of illness or disease.
Fragile Sites and Cancer
- FHIT: Fragile Histidine Triad
- Located within a fragile site on chromosome 3.
- Altered in cells taken from tumors in individuals with lung cancer.
- Is also a part of another fragile region, FRA3B, which is linked to other cancers (e.g., esophagus, colon, and stomach).
FHIT
- Highly susceptible to induced breaks in DNA.
- Sensitive to carcinogen-induced damage, creating susceptibility to cancer.
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Description
Explore the intriguing world of chromosome mutations, including aneuploidy and polyploidy. This quiz covers various types of chromosomal changes and their implications on genetic conditions like Down syndrome. Test your understanding of how these mutations can affect cellular functions and evolution.
