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
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.
__: the production of offspring with combos of traits that differ from those found in either parent
__: an offspring with a phenotype that matches one of the parental phenotypes; also called the phenotype itself
__: an offspring whose phenotype differs from that of the parents (__)
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.
frequency of recombination x2
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 __.
__ breaks the physical connection between specific alleles of genes on the same chromosome, and accounts for the __ of lined genes.
The __ from crossing over may bring alleles together in new combos, and the subsequent events of meiosis distribute the __ to gametes.
recombinant chromosomes x2
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
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.
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.
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
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
A genetic map based on recombination frequencies is a __.
Sturtevant expressed the distances between genes in __, defining one map unit as equivalent to a __ recombination frequency. Today, map units are often called __.
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.
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 __.
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.)
A __ does portray the order of genes along a chromosome, but it does not accurately portray the precise locations of those genes.
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.
The ultimate maps show the physical distances between gene loci in __.
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.