The following genes are on one arm of chromosome 9 in the order indicated. C giv
ID: 71282 • Letter: T
Question
The following genes are on one arm of chromosome 9 in the order indicated.
C gives colored seeds, c gives white
Bz gives green leaves, bz bronze
Wx gives starchy seeds, wx waxy
Sh gives smooth seeds, sh shrunken
D gives tall plants, d dwarf
A plant homozygous for all 5 recessive alleles is crossed with a newly-found plant that is homozygous for all 5 dominant alleles. The F1 hybrid is back-crossed to the recessive parent, and the following classes and proportions of progeny are produced.
Colored, green, starchy, smooth, tall 360
White, bronze, waxy, shrunk, dwarf 355
Colored, bronze, waxy, shrunk, dwarf 40
White, green, starchy, smooth, tall 46
Colored, green, starchy, smooth, dwarf 85
White, bronze, waxy, shrunk, tall 84
Colored, bronze, waxy, shrunk, tall 8
White, green, starchy, smooth, dwarf 9
Colored, green, waxy, smooth, tall 7
White, bronze, starchy, shrunk, dwarf 6
How many classes of progeny are “missing?” (1 pt)
From your cross data, calculate the observed genetic distances between adjacent genes. Which genes have genetic distances different from the expected values? Based on these data, draw a map of the likely gene order in the newly-found plant (4 pts)
Explanation / Answer
Based on the given data,
The total number of genes = 5
The pattern of dominance is:
The genotype of plant homozygous for all 5 recessive alleles is: c, bz, wx, sh, d
The genotype of plant homozygous for all 5 dominant alleles is: C, Bz, Wx, Sh, D
The cross between these two plants is as follows:
Form this cross, the obtained F2 is as follows:
Therefore, the phenotypic ratio is 1: 1: 1: 1: 1: 1: 1: 1: 1: 1.
(a)
Form the obtained progeny twelve classes are “missing.” The cross between the five genes should give 22 classes, but it has only given 12 classes.
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