Chapter 15: The Chromosomal Theory of Inheritance

  1. There are more genes than chromosomes, because each chromosome contains hundreds of genes.
    Genes located on the same chromosome that tend to be inherited together in genetic crosses are __.
    __: a single gene on a sex chromosome
    __: two or more genes on the same chromosome that tend to be inherited together
    • linked genes
    • sex-linked
    • linked genes
  2. In Morgan's corsses with linked genes (gray bodies/ normal sized wings), he observed a much higher proportion of __ than would be expected if the two genes assorted independently.
    Based on the results, he concluded that body color and wing size are usually inherited together n specific combos (__) because the genes for these characters are on teh same chromosome.
    However, __ are also produced. In the experiment, this showed that body-color and wing-size genes are only partially linked genetically.
    • parental phenotypes
    • parental combinations
    • nonparental phenotypes
  3. __: the production of offspring with combos of traits that differ from those found in either parent
    genetic recombination
  4. __: an offspring with a phenotype that matches one of the parental phenotypes; also called the phenotype itself
    parental types
  5. __: an offspring whose phenotype differs from that of the parents (__)
    • recombinant types
    • recombinants
  6. When 50% of all offspring are __, geneticists say that there is a 50% __.
    -- A 50% __ in such testcrosses is observed for any two genes that are located on different chromosomes and are thus unlinked. The physical basis of __ between unlinked genes is the random orientation of __ at __ of meiosis, which leads to the independent assortment of the two unlinked genes.
    • recombinants
    • frequency of recombination x2
    • recombination
    • homologs
    • metaphase I
  7. In Morgan's experiment, most of the offspring had __, suggesting that the two genes were on the same chromosomes, since the occurrence of parental types with a frequency greater than __ indicates that genes are linked. About __ of the offspring were __.
    • parental phenotypes
    • 50%
    • 17%
    • recombinants
  8. __ breaks the physical connection between specific alleles of genes on the same chromosome, and accounts for the __ of lined genes.
    • Crossing over
    • recombination
  9. The __ from crossing over may bring alleles together in new combos, and the subsequent events of meiosis distribute the __ to gametes.
    recombinant chromosomes x2
  10. Fertilizaion of various classes of eggs by __ produced an offspring population in which __ exhibited a nonparental, recombinant phenotype.
    -- The percentage of recombinant offspring, the __, is related to the distance between linked genes.
    • homologous recessive sperm
    • 17%
    • recombination frequency
  11. The discovery of linked genes and recombination due to crossing over led Sturtevant to a method for constructing a __, an ordered list of the genetic loci along a particular chromosome.
    genetic map
  12. Sturtevant hypothesized that __ calculated from experiments depend on the distances between genes on a chromosome. He assumed that __ is a random event, with the chance of crossing over approximately equal at all points along a chromosome.
    • recombination frequencies
    • crossing over
  13. Based on these assumptions, he predicted that, what did Sturtevant predict?
    the farther apart two genes are, the higher the probability that a crossover will occur betewen them and therefore the higher the recombination frequency
  14. Sturtevant's reasoning for his prediction (the farther...) was __.
    -- Using __ data from various fruit fly crosses, he proceeded to map genes- assign relative positions to genes on the same chromosomes
    • the greater the distance between two genes, the more points there are between them where crossing over can occur
    • -- recombination
  15. A genetic map based on recombination frequencies is a __.
    linkage map
  16. Sturtevant expressed the distances between genes in __, defining one map unit as equivalent to a __ recombination frequency. Today, map units are often called __.
    • map units
    • 1%
    • centrimorgans
  17. The observed frequency of recombination in crosses involving two such genes can have a maximum value of __, a result indistinguishable from that for genes on different chromosomes.
    -- In this case, the physical connection between genes on the same chromosome is not reflected in the results of genetic crosses.
    - Despite being on the same chromosome and thus being __, the genes are __; alleles on such genes assort independently, as if they were on different chromosomes.
    • 50%
    • physically linked
    • genetically unlinked
  18. In the fruit fly cells, the __ thus provided additional evidence that genes are located on chromosomes. Each chromosome has a linear array of specific genes, each with its own __.
    • linkage map
    • locus
  19. Because a __ is based only on recombination frequencies, it gives only an approximate picture of a chromosome. The frequency of __ is not actually uniform over the length of a chromosome as Sturtevant assumed, and therefore __ do not correspond to actual physical distances (in nanometers, for ex.)
    • linkage map
    • crossing over
    • map units
  20. A __ does portray the order of genes along a chromosome, but it does not accurately portray the precise locations of those genes.
    linkage map
  21. Other methods enable geneticists to construct __ of chromosomes, which locate genes with respect to chromosomal featurs, such as stained bands, that can be seen in the microscope.
    cytogenetic maps
  22. The ultimate maps show the physical distances between gene loci in __.
    DNA nucleotides
  23. Comparing a __ with such a physical map or with a __ of the same chromosome, we find that the linear order of genes is identical in all the maps, but the spacing between genes is not.
    • linkage map
    • cytogenetic map
Card Set
Chapter 15: The Chromosomal Theory of Inheritance
AP Bio