Download Genetics Problems

GENETICS PRACTICE PROBLEMS
Genetics Problems
Steps:
a.
b.
c.
d.
e.
f.
Define all terms (phenotype, genotype for all individuals)
State parental cross
Set up proper Punnett square (male gametes on top)
Complete all Punnett square combinations
Do a genotypic and phenotypic analysis of the offspring
Answer questions stated in the problem
1. On planet Zibzab, having blue hair (B) is dominant over yellow hair (b). A homozygous bluehaired male is married to a homozygous recessive female. Can they produce any yellow-haired
offspring?
2. In humans, farsightedness (F) is dominant over normal vision (f). Determine the percentage of
their offspring that would need glasses resulting from the parental cross of a heterozygous farsighted man and a woman with normal eyesight.
3. Short hair (S) is dominant over long hair (s) in rabbits. Determine the probable offspring of the
mating of a male homozygous short-haired rabbit and a female homozygous long-haired rabbit.
4. In humans, brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man marries a
brown-eyes woman whose father had blue eyes. What percentage of their children would you
predict will have blue eyes?
5. Yellow coat color in guinea pigs results from the homozygous genotype YY; crème-color by the
heterozygous Yy; white color from the homozygous genotype yy. What will the phenotypic rations
be if two crème-colored individuals are mated? What would the phenotypic ration be if this were a
case of complete dominance?
6. Suppose two new-born babies were accidentally mixed up in a hospital, something that rarely
happens. In an effort to determine the parents of each baby, the blood types of the babies and
parents were determined through anti-sera tests. Which baby belongs to which parents? What are
the actual genotypes of each parent and baby?
Baby 1- type O
Baby 2-type A
Mrs. Estevez- type B
Mr. Estevez- type AB
Mrs. Bahar- type B
Mr. Bahar- type B
7. If factor “a” is lethal in the homozygous recessive condition, what percentage of offspring will
survive from a cross between a male with the genotype AaBb and a female who is also
heterozygous for both traits?
8. In the fruit fly Drosophila melanogaster, vestigial wings (ww) and hairy body (hh) are
produced by two recessive genes located on different chromosomes. The normal alleles, long
wings (W) and hairless body (H) are dominant. Suppose a vestigial-winged, hairy male is
crossed with a female that is heterozygous for both traits. What percentage of the offspring will
be purebred for both traits?
9. Some Drosophila have defective wings. They may have a defect in their "curly gene," which is
on the second chromosome. Having curled wings is a dominant (C) mutation, which means
that only one copy of the gene has to be altered to produce the defect. In fact, if both copies are
mutated (CC), the flies do not survive. What percentage of offspring will survive and have
normal wings from a cross of two heterozygous parents?
10. In Drosophila, normal fruit flies are called "wildtypes." In wildtype flies the eye color is
bright red (R). Some flies have a mutation which produces white eyes (r); they have a defect in
their "white" gene. In these flies, the white gene is totally defective: it produces no red pigment
at all. In "wildtypes" the antennas stick out in front of their red eyes (L). Some flies have
abnormal, leg-like antennas on their foreheads (l). They have a defect in their "antennapedia"
gene (Latin for "antenna-leg"), which normally instructs some body cells to become legs. In
these flies, the antennapedia gene falsely instructs cells that would normally form antenna to
become legs instead. What percentage of offspring would express a mutant phenotype (for
either trait) from a cross of two dihybrids?
11. Wildtype flies have black-and-tan striped bodies (Y). Some flies are more yellow in body color
than normal flies. They have a defect in their "yellow gene," which is on the X chromosome.
Since the yellow gene is needed for producing a fly's normal black pigment, yellow mutant
flies (y) cannot produce this pigment. Cross two heterozygous striped flies. If a predator
preferentially ate the striped flies because they were easier to see, what percentage of offspring
would survive this cross?
12. 2:1 segregation in Manx cats: Manx cats are heterozygous for a dominant mutation that results
in no tails (or very short tails), large hind legs, and a distinctive gait. The mating of two Manx
cats yields two Manx kittens for each normal, long-tailed kitten, rather than three-to-one as
would be predicted from Mendelian genetics. Therefore, the mutation causing the Manx cat
phenotype is likely a(n) __________ allele.
http://www.exploratorium.edu/exhibits/mutant_flies/mutant_flies.html
Expected genotype ratio
The expected genotype ratio when two heterozygotes are crossed is 1 (homozygous dominant) : 2
(heterozygous) : 1 (homozygous recessive). When a phenotypic ratio of 2 : 1 is observed, there is
probably a lethal allele. Individuals homozygous for the lethal allele (tt in this case) do not survive
embryonic development, and are not born. The heterozygotes have a phenotype distinct from normal
cats.
PRACTICE PROBLEMS
In Drosophila, normal fruit flies are called "wildtypes." In
wildtype flies the eye color is bright red (A). Some flies have a
mutation which produces white eyes (a); they have a defect in
their "white" gene. In these flies, the white gene is totally
defective: it produces no red pigment at all. What percentage of
offspring would express a mutant phenotype from a cross of two
hybrids (“monohybrid cross”)?
In the fruit fly Drosophila melanogaster, a hairy body (aa) is
produced by two recessive genes. The normal allele for a
hairless body (A) is dominant. Suppose a hairy male is crossed
with a female that is heterozygous. What percentage of the
offspring will be purebred?
Some Drosophila have defective wings. They may have a defect
in their "curly gene," which is on the second chromosome.
Having curled wings is a dominant (A) mutation, which means
that only one copy of the gene has to be altered to produce the
defect. In fact, if both copies are mutated (AA), the flies do not
survive. What percentage of offspring will survive and have
normal wings from a cross of two heterozygous (hybrid)
parents?