Sex-Linked Questions
1. Red/ green colour blindness in humans is a sex-linked recessive trait. In a large family in which all the daughters have normal visions and all the sons are colourblind, what are the probable genotypes of the parents?
2. If a normal sighted woman whose father was colourblind marries colour blind man, what percentage of their sons will be colour blind? What percentage of their daughters will be colour blind?
3. If a normal woman carrying the sex linked gene for colour blindness marries a normal male, what percentage of their sons will be colour blind? What if she marries a colour blind male?
4. Baldness is a recessive sex-linked trait. If a normal headed woman whose father is bald, has children with a normal headed man, whose father was bald, what will be the genotypes and phenotypes of their children?
Gene Mapping Questions
1. The crossover frequency between genes E and F is 6%, between E and G is 10% and between F and G is 4%. Construct a gene map. Determine the sequence of genes on the chromosome.
2. In 1911, Thomas Morgan collected the following crossover gene frequencies while studying Drosophila. Bar-shaped eyes are indicated by the B allele, and carnation eyes are indicated by the allele C. Fused veins on wings (FV) and scalloped wings (S) are also located on the same chromosome.
Gene Combinations / Frequencies of RecombinationsFV/B / 2.5%
FV/C / 3.0%
B/C / 5.5%
B/S / 5.5%
FV/S / 8.0%
C/S / 11.0%
Construct a gene map. Determine the sequence of genes on the chromosome.
3. The following chart shows crossover frequencies for some genes on an autosome of organism Z. Construct a chromosome map. Order the genes on the chromosome.
GenesCrossover Frequency
PQ5%
PR8%
PS12%
QR13%
QS17%
4. For a series of experiments, a linkage group composed of genes W, X, Y and Z was found to show the following gene combinations. (All recombinations are expressed per 100 fertilized eggs). Construct a gene map. Determine the sequence of genes on the
chromosome.
Genes / W / X / Y / ZW / – / 5 / 7 / 8
X / 5 / – / 2 / 3
Y / 7 / 2 / – / 1
Z / 8 / 3 / 1 / –
5. For a series of experiments, a linkage group composed of genes A, B, C and D was found to show the following gene combinations. (All recombinations are expressed per 100 fertilized eggs). Construct a gene map. Determine the sequence of genes on the chromosome.
Genes / A / B / C / DA / – / 12 / 15 / 4
B / 12 / – / 3 / 8
C / 15 / 3 / – / 11
D / 4 / 8 / 11 / –
6. In Drosophila, the genes for eye colour (pr), wing shape (vg), and body colour (eb) are all found on the same chromosome. The following crossover frequencies for these genes were determined by experimentation.
GenesCrossover Frequency
prvg12.5%
preb6.0%
vgeb18.5%
Construct a gene map. Determine the sequence of genes on the chromosome.
7. Using the following chart, construct a gene map and determine the sequence of genes
on the chromosome.
GenesCrossover Frequency
AB24.0%
AC8.0%
CD2.0%
AF16.0%
FB8.0%
DF6.0%
8. Five traits found in Drosophila on the same chromosome are yellow body colour (y), white eye colour (w), vermilion eye colour (v), miniature wing (m) and rudimentary wing (r). Given the following crossover frequencies, construct a gene map and correctly order
the genes on this chromosome.
GenesCrossover Frequency
yw2.2%
vm3.0%
vr26.6%
vw30.0%
vy32.2%
wm33.0%
ym35.2%
wr56.6%