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Chromosomal Basis of Inheritance - General Biology

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  • Chromosome Theory of Inheritance
    States that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
  • Why are fruit flies a good model organism for genetic studies?
    They have many offspring, breed every two weeks, and have only four pairs of chromosomes.
  • Wild type vs. Mutant in Drosophila
    Wild type refers to the normal phenotype, while mutant refers to an altered phenotype due to a genetic mutation.
  • Morgan's experiment with white-eyed Drosophila
    Showed that the white eye trait is X-linked recessive, as only males with the Xw allele showed white eyes.
  • X-linked recessive traits examples
    Color blindness, Duchenne muscular dystrophy, and hemophilia are caused by X-linked recessive alleles.
  • Hemizygous definition
    Having only one allele for a gene in a diploid organism, such as males for X-linked genes.
  • Cross that cannot produce white-eyed male Drosophila
    Cross between homozygous red-eyed females and white-eyed males cannot produce white-eyed males.
  • Chromosomal sex determination systems
    Include X-Y system, X-0 system, Z-W system, and haplo-diploid system.
  • Barr body
    An inactivated X chromosome in female mammals that forms a dense body in the nucleus.
  • Effect of linkage between two genes on inheritance
    Linked genes tend to be inherited together, deviating from the expected 1:1:1:1 ratio of independent assortment.
  • Genetic recombination frequency for unlinked genes
    Parental and recombinant types occur at approximately 50% frequency each.
  • Genetic recombination frequency for linked genes
    Recombinant types occur less than 50%, indicating genes are physically close on the same chromosome.
  • Genetic map (linkage map)
    A map showing the relative positions of genes on a chromosome based on recombination frequencies.
  • Map unit definition
    One map unit corresponds to a 1% recombination frequency between two genes.
  • Aneuploidy
    The presence of an abnormal number of chromosomes in a cell, such as monosomy or trisomy.
  • Polyploidy
    Having more than two complete sets of chromosomes, e.g., triploidy (3n) or tetraploidy (4n).
  • Down syndrome cause
    Trisomy 21, an extra copy of chromosome 21.
  • Klinefelter syndrome
    A condition in males with an extra X chromosome (XXY).
  • Turner syndrome
    A condition in females with only one X chromosome (XO).
  • Types of chromosomal structural alterations
    Deletion, duplication, inversion, and translocation.
  • Cri du chat syndrome
    A disorder caused by a deletion on chromosome 5.
  • Chronic myelogenous leukemia (CML)
    Caused by a translocation between chromosomes 9 and 22.
  • Genomic imprinting
    An epigenetic phenomenon where expression of an allele depends on its parental origin.
  • Nondisjunction
    Failure of homologous chromosomes or sister chromatids to separate properly during meiosis.