Biology 190 - Genetics Problems - Set 1
Due by Tuesday, October 30 at 11:59 pm
1. Fin length in guppies is determined by a single gene. The dominant allele, L, produces a fish
with fins of normal length, while the recessive allele, l, produces a fish with long fins.
You cross a normal-finned male guppy with a long-finned female, and the resulting F1 progeny
come out 50% normal-finned and 50% long-finned.
a. What was the genotype of the male with regard to the alleles for fin length?
b. If two of the normal-finned F1 offspring are crossed with each other, what would you expect
the genotype and phenotype ratios of those offspring to be?
A male F1 guppy with normal fins is crossed with a long-finned female. What are the chances
that
c. Their first offspring will have long fins?
d. Their first five offspring all will have normal fins?
e. Two or more of their first five offspring will have long fins?
A male F1 guppy with normal fins is crossed with a female F1 guppy with normal fins. What
are the chances that
f. Their first offspring will have normal fins?
g. Their first three offspring all will have normal fins?
h. Two or more of their first three offspring will have long fins?
2. Tail fins in guppies may be normal or forked. The allele for a normal tail (F) is dominant and
the allele for a forked tail (f) is recessive. A cross between a heterozygous individual
with a normal tail (not long and not forked) and a guppy with a long, forked tail results in
offspring with the following phenotypes and proportions: 44% normal, 44% long &
forked, 6% normal & forked, 6% long but not forked.
a. Are the genes for tail length and forking linked?
b. If linked, how far apart are these two genes, in map units?
3. Flower color in morning glories is controlled by a single locus with two incompletely
dominant alleles. R1R1 plants produce red flowers, R2R2 plants produce blue flowers and
R1R2 plants produce purple flowers. What phenotype ratios would result from the
following crosses?
a. A red-flowered plant and a blue-flowered plant.
b. Two purple-flowered plants.
c. A red-flowered plant and a purple-flowered plant
4. Red-green color blindness is X-linked in humans. If a male is red-green color blind, and both
parents have normal color vision, which of the male's grandparents is most likely to be
red-green color blind?
5. Body color in seahorses is controlled by two unlinked loci. The first locus has three alleles:
B1, B2 and b. B1 and B2 are codominant while b is recessive. Individuals with B1 but not
B2 are red, animals with B2 but not B1 are yellow, seahorses with both B1 and B2 are black
and individuals with neither B1 nor B2 are brown. The second locus has two alleles and
regulates synthesis of a pigment-producing enzyme. Presence of the dominant allele, W,
leads to pigmented seahorses, while absence of the dominant allele leads to albinos.
A black male is crossed with a red female. What are the genotypes of the two parents if the
offspring phenotype ratios are:
a. Red:Black:Albino = 3:3:2
b. Red:Black:Yellow:Albino = 6:3:3:4
A red male is crossed with an albino female. What are the genotypes of the two parents if the
offspring phenotype ratios are:
c. Red:Black = 1:1
d. Red:Brown = 1:1
e. Red:Black:Yellow = 2:1:1
f. Red:Black:Yellow:Brown:Albino = 1:1:1:1:4