A brown-eyed man whose father was brown-eyed and whose
mother was blue-eyed married a blue-eyed woman whose mother
and father were both brown-eyed. The couple has a blue-eyed
son. What are the genotypes of all individuals?
In human beings, brown eyes are usually dominant over blue
eyes. Suppose a blue-eyed man marries a brown-eyed woman
whose father was blue-eyed. What proportion of their
children would you predict to have blue eyes?
In horses, B = black, b = brown, T = trotter, t = pacer. A
black pacer mated to a brown trotter produces a black
trotter offspring year after year. What are the probable
genotypes?
In humans, freckles are dominant to no freckles. A man with
freckles is married to a woman with freckles, but the
children have no freckles. What's the reason?
In mice colored coat is dominant to albinism. Sniffles, a
male mouse with a colored coat is mated to Esmeralda, an
alluring albino. The resulting litter of six young all had
colored fur. The next time around Esmeralda was mated with
Whiskers, who was the same color as Sniffles; some of this
litter were white.
a)What are the probable genotypes of Sniffles, Esmeralda,
and Whiskers?
b) If a male of the 1st litterwas mated to a colored female
of the 2nd litter, what phenotypic ratio might be expected
among the offspring?
c)What would be the expected results if a male of the 1st
litter was mated to an albino from the 2nd?
A number of plant species have a recessive allele for
albinism; homozygous albino (white) individuals are unable
to synthesize chlorophyll. If a tobacco plant heterozygous
for albinism is allowed to self-pollinate and 500 seeds
germinate: a)how many offspring will be the same genotype
as the parent? b)how many seedlings would you expect to be
white?
In snapdragons tallness (T) is dominant to dwarfness (t).
Red flowers are produced by RR and white flowers by rr but
the heterozygous Rr is pink. A dwarf red snapdragon is
crossed to a homozygous tall plant with white flowers. What
is the phenotypic ratio of the F1? the F2?
The weight of the fruit of one variety of squashes is
determined by three pairs of genes: AABBCC produces 6 lb
squashes and aabbcc produces 3 lb squashes. Each dominant
allele adds 1/2 lb tothe base weight (3 lb). If a pure
breeding line that produced 6 lb squashes was crossed with
a pure breeding line that produced 3 lb squashes, what
would be the phenotypic ratio of the F1 and the F2?
Consider two linked autosomal genes. The dominant allele C
of the first gene causes cataracts of the eye, whereas its
recessive allele produces normal eyes. The dominant allele
P causes polydactyly (an extra finger) whereas its allele
(p) produces a normal number of fingers. A man with
cataracts and normal fingers marries a woman with
polydactyly and normal eyes. Their son has both polydactyly
and cataracts and he marries a woman with neither trait.
What is the probability that their first child will have
cataracts and polydactyly?
The rare trait of ocular albinism (almost complete absence
of eye pigment) is inherited as a sex-linked recessive. A
man with ocular albinism marries a woman who neither has
this trait nor is a carrier. What would you predict about
their offspring concerning this trait?
The ABO blood system has been employed to settle cases of
disputed paternity. Suppose, as an expert in genetics, you
are called to testify in a case where the mother is type A,
the child is type O and the alleged father is type B. How
would you respond to the following statements of the
attornies:
a. "Since the mother has type A, the type O of the child
must have come from the father and since my client is type
B, he obviously could not have fatered the child." Made by
the attorney of the alleged father.
b. "Further tests revealed that this man is heterozygous
and therefore he must be the father." Made by the mother's
attorney.
In cats yellow is due to gene B and black to its allele b.
These genes are located on the X chromosome (sex-linked).
The heterozygous results in calico (tortoise shell). What
kinds of offspring (sex & color) are expected from the
cross: black male & calico female? Most calico males are
sterile, why?
A certain man has the genotype AaBb; genes A and B are on
one chromosome and a and b are on its homologue. List the
gametes that could be formed with crossing over and with no
crossing over
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