Item Bank: Codominant/Multiple Alleles/Dihybrid Crosses/Pedigrees/Recombination
- A classical example of
multiple alleles is found in the ABO blood group system of humans, where
the allele IA for the A antigen is codominant with the
allele IB for the B antigen. Both IA
and IB are completely dominant to the allele i,
which fails to specify any detectable antigenic structure. The hierarchy of dominance
relationships is symbolized as (IA = IB)
man is suing his wife for divorce on the grounds of infidelity. Their first child and second child, whom
they both claim, are blood groups O and AB, respectively. The third child, whom the man disclaims, is
blood type A. Is it possible that the man
is the father of the third child? EXPLAIN!!!
- Thalassemia is a hereditary
disease of the blood of humans resulting in anemia. Severe anemia (thalassemia major) is
found homozygous (TMTM) and a milder form of
anemia (thalassemia minor) is found in heterozygotes (TMTN). Normal individuals are homozygous TNTN. If all individuals with thalassemia
major die before sexual maturity, (a) what proportion of the adult F1
from marriages of thalassemia minors by normals would expected to be
normal, (b) what fraction of the adult F1 from marriages of
minors by minors would be expected to be anemic?
- The inheritance of coat
colors of cattle involves a multiple allelic series with a dominance
hierarchy as follows: S > sh > sc
> s. The S allele
puts a band of white color around the middle of the animal and is referred
to as the Dutch belt; the sh allele produces
Hereford-type spotting; solid color is a result of the sc
allele; and Holstein-type spotting is due to the s allele. Homozygous Dutch belted males are crossed
to Holstein-type spotted females.
The F1 females are crossed to a Hereford-type spotted
male of genotype shsc. Predict the genotypic and phenotypic
frequencies in the progeny.
- In fruit flies, we can
consider two traits, cinnabar eye color (recessive) and black body color
(recessive). Wild-type eye color (cn+)
will result in the reddish eye color, whereas wild-type body color (b+)
will result in a brownish body color.
If we cross a heterozygous fruit fly (for both traits) by a completely
homozygous recessive fruit fly, what would be the expected phenotypic
ratios in the F1?
- The gene for spotted coat
color in rabbits (s+) is dominant to its allele for
solid color (s). In the
following pedigree assume that those individuals brought into the family
from outside do not carry the gene for solid color, unless there is
evidence to the contrary.
- Write the
genotype for each individual insofar as you can definitively ascertain.
- What s
the probability of progeny having the solid phenotype from a mating
between III-2 and III-6.
- A multiple allelic series is
know to govern the intensity of pigmentation in the mouse such that D
= full color, d = dilute color, and dl is lethal
when homozygous. The dominance
order is D > d > dl. A full-colored mouse carrying the
lethal is mated to a dilute-colored mouse also carrying the lethal. The F1 is backcrossed to the
dilute parent. (a) What phenotypic
ratio is expected in the viable backcross progeny? (b) What percentage of full-colored
backcross progeny carry the lethal?
(c) What fraction of the dilute-colored progeny carry the lethal?
- The shape of radishes may be
long (SLSL), round (SRSR),
or oval (SLSR). If long radishes are crossed to oval radishes and the F1
the allowed to cross at random among themselves, what phenotypic ratio is
expected in the F2?
- The Palomino horse is a
hybrid exhibiting a golden color with lighter mane and tail. A pair of codominant alleles (D1
and D2) is known to be involved in the inheritance of
these coat colors. Genotypes
homozygous for the D1 allele are chestnut-colored
(reddish), heterozygous genotypes are Palomino-colored, and genotypes
homozygous for the D2 allele are almost white and called
cremello. (a) From matings between
Palominos, determine the expected Palomino:Non-Palomino ratio among the
offspring. (b) What percentage of
the non-Palomino offspring in part (a) will breed true? (c) What kind of
breeding will produce only Palomino?
- A pair of codominant alleles
is known to govern cotyledon leaf color in soybeans. The homozygous genotype CGCG
produces dark green, the heterozygous genotype CGCY
produces light green, and the other homozygous genotype CYCY
produces yellow leaves so deficient in chloroplasts that seedlings do not
grow to maturity. If dark-green
plants are pollinated only by light-green plants and the F1
crosses are made at random to produce an F2, what phenotypic
and genotypic ratios would be expected in the mature F2 plants?
- The coat colors of many
animals exhibit the “agouti” pattern, which is characterized by a yellow
band of pigment near the tip of the hair.
In rabbits, a multiple allelic series is known where the genotypes EDED
and EDe produce only black (nonagouti), but the
heterozygous genotype EDE produces black with a trace of
agouti. The genotypes EE or
Ee produce full color, and the recessive genotype ee
produces reddish-yellow. What phenotypic and genotypic ratios would be
expected in the F1 and F2 from the cross (a) EDED
X Ee, (b) EDe X EE?