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Tweaking the Experiment
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First Experiment



1

The banding patterns observed in the ultra-bar and bar-revertant flies can be explained by
A)A misaligned crossover between two X chromosomes
B)A new mutation creating a bar allele
C)The loss of an X chromosome in a female fly
D)An abnormality in chromosome staining
2

Let's assume that a crossover requires an alignment between a minimum of one eye facet gene as shown in the figure that follows this experiment. Based on this assumption, if Bridges had begun with a true-breeding strain of ultra-bar flies, it would have been possible to obtain flies with the following number of eye-facet genes on their X chromosomes.
A)One, two, three, four, five, and six
B)Zero, one, two, three, four, and five
C)One, two, three, four, and five
D)Zero, one, two, three, four, five, and six
3

With regard to this experiment, a "position effect" is observed because
A)A bar heterozygote has more facets than a bar homozygote.
B)A bar homozygote has more facets than an ultra-bar heterozygote.
C)A bar homozygote has more facets than an ultra-bar homozygote.
D)An ultra-bar heterozygote has more facets than an ultra-bar homozygote.
4

The advantage of examining polytene chromosomes is
A)That's where the facet gene is found.
B)Their large size makes it possible to detect single gene duplications.
C)They are easier to stain compared to nonpolytene chromosomes.
D)They are very small, making them easy to manipulate.
5

The data indicate that
A)Bar-eyed flies have three copies of the eye-facet gene on their X chromosome.
B)Ultra-bar eyed flies have three copies of the eye-facet gene on their X chromosome.
C)Bar-revertants have two copies of the eye-facet gene on their X chromosome.
D)Ultra-bar eyed flies have two copies of the eye-facet gene on their X chromosome.







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