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Variations in Chromosome Structure and Number - Genetics

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Termini in questo insieme (23)

  • What is genetic variation?
    Genetic variation refers to genetic differences between members of the same species, including allelic variation, chromosome mutations, and genome mutations.
  • What is a karyotype?
    A karyotype is a cytogenetic study of chromosome structure under a microscope, used to detect extra or missing chromosomes or large structural changes.
  • How are chromosomes characterized?
    Chromosomes are characterized by size, shape (centromere position), and banding pattern (stained dye bands).
  • What do the chromosome arms p and q represent?
    p is the short arm and q is the long arm of a chromosome, defined by the centromere position.
  • What are the four main types of chromosome structural mutations?
    The four main types are deletions (deficiencies), duplications, inversions, and translocations.
  • What is a deletion (deficiency) mutation?
    A deletion results in a net loss of genetic material and can cause deleterious phenotypic changes.
  • How do duplications occur and what is their effect?
    Duplications usually result from abnormal crossing over, often cause no phenotype or mild effects, and provide raw material for evolution.
  • What is the Bar eye phenotype in Drosophila an example of?
    The Bar eye phenotype is an example of a gene duplication causing a visible phenotype and demonstrating the positional effect.
  • What is the positional effect in genetics?
    The positional effect occurs when the location of a gene affects its expression and phenotype, even if gene copy number is the same.
  • What is a gain-of-function mutation?
    A gain-of-function mutation causes a new or enhanced activity of a protein, unlike loss-of-function mutations which reduce or abolish function.
  • What are gene families?
    Gene families are groups of similar genes derived from a common ancestral gene, often formed by gene duplications.
  • What are inversions and their types?
    Inversions are chromosome rearrangements that do not cause net loss of genetic material; types include paracentric (not involving centromere) and pericentric (involving centromere).
  • How do inversions affect gamete formation?
    Inversion heterozygotes form inversion loops during meiosis, which can lead to abnormal gametes due to improper crossing over.
  • What are translocations and their types?
    Translocations involve exchange of chromosome segments without net gain or loss; types include simple and reciprocal translocations.
  • How do translocations affect fertility?
    Translocations often cause fertility problems by disrupting chromosome pairing and segregation during meiosis.
  • Define euploidy and examples.
    Euploidy is having chromosomes in exact multiples of a set (n), e.g., haploid (1n), diploid (2n), triploid (3n), tetraploid (4n).
  • What is aneuploidy?
    Aneuploidy is having an abnormal number of chromosomes, not a complete set, such as trisomy (extra chromosome) or monosomy (missing chromosome).
  • Why is trisomy or monosomy usually detrimental?
    Because gene expression is imbalanced, leading to too much or too little protein production, causing developmental and health issues.
  • What causes aneuploidy?
    Aneuploidy is caused by nondisjunction during meiosis I or II, or mitosis, leading to incorrect chromosome segregation.
  • What is autopolyploidy?
    Autopolyploidy is having extra sets of chromosomes from the same species, e.g., tetraploid with four copies of each chromosome.
  • What is alloploidy and allopolyploidy?
    Alloploidy has one set of chromosomes from two species; allopolyploidy has two or more complete sets from two species, often fertile if even-numbered sets.
  • Why are alloploids often sterile?
    Because chromosomes from different species often lack homologues, preventing proper pairing and haploid gamete formation during meiosis.
  • Give examples of sterile and fertile hybrids.
    The mule (horse x donkey) is sterile; the beefalo (bovine x buffalo) is fertile due to chromosome compatibility.