GENETICS PROBLEMS: Include the appropriate Punnett Squares to demonstrate how you answered each problem or receive no credit.
Some of the problems are taken from the end of chapter exercises or the website.
- In peas, tall plants are dominant to short plants. Complete a punnett
square to show the genotypes and phenotypes expected for the following
cross: heterozygous tall x heterozygous tall
- In humans, the gene for brown eyes (b) is dominant to the gene for blue
eyes and the gene for right handedness (r) is dominant to the gene for left
handedness. Two individuals heterozygous for both of these characteristics
- Complete a punnett square to show the expected genotypes and
phenotypes of the offspring.
- Summarize the ratio of the phenotypes
- In chimpanzees, straight fingers are dominant to bent fingers. Complete a
punnett square to show the genotypes and phenotypes expected for the
following cross: heterozygous straight x homozygous bent
- In four o'clock flowers, red plants are homozygous for the allele (R) of
the gene for flower color. Plants with white flowers are homozygous for the
(r) allele of the same gene. Plants with pink flowers are are heterozygous
for these two alleles. Complete a punnett square to show genotypes and
phenotypes that are expected when plants with pink flowers are intercrossed.
- The long hair of persian cats is recessive to the short hair of siamese
cats, but the black coat of persians is dominant to the brown and tan coat
of siamese. Mating of persians with siamese cats produces an f1 generation
heterozygous for both of these characteristics. Complete a punnett square to
show the expected genotypes and phenotypes of the offspring from the mating
of these f1 heterozygous cats.
- As in labrador retrievers, fur color in mice is governed by genes
concerned with producing and distributing melanin. At one gene location, a
dominant allele (b) specifies dark brown and a recessive gene (b) specifies
a tan coat. At another gene location, a dominant allele permits melanin
production and a recessive allele (c) shuts it down, resulting in the
production of an albino mouse. Complete a punnett square to show the
expected phenotypes and genotypes resulting from crossing a true breeding
brown mouse with an albino mouse that is homozygous recessive for both
genes. (5 points)
- Complete a punnett square to show expected the phenotypes and genotypes
resulting from interbreeding the the offspring produced in the above
experiment (5 points)
- The x-linked barred locus in fruit flies controls the pattern of the
wings, with the alleles (b) for barred pattern and (b) for no bars. A male
with barred wings is mated to a non-barred female. Complete a punnet square
to show the expected genotypes and phenotypes of the offspring
- Muscular dystrophy is a sex-linked recessive disorder. A man with muscular
dystrophy marries a woman who does not have this disease. Half of their
daughters and half of their sons develop this disease. What is the genotype
of the father? The mother? Document how you arrived at your answer or
receive no credit
- Colorblindness is a sex-linked recessive character. A color blind woman
marries a male with normal color vision (c).
- What are the genotypes of each?
- Complete a punnett square to show what the expected average phenotypes
and genotypes of their offspring will be.
- In radishes, two incompletely dominant genes control color and shape. Red
and white radishes are homozygous, whereas the hybrid is purple. Long and
round radishes are homozygous and if crossed will produce an oval hybrid.
Complete a punnet square to show the genotypes and phenotypes produced by
crossing pure breeding red long radishes with white round radishes.
- Suppose you identify a new gene in mice. One of its alleles specifies white fur color. A second allele specifies brown fur color. You want to determine whether the relationship between the alleles is simple dominance (and if so which color is dominant) or incomplete dominance. What sorts of genetic crosses would give you the answer? On what types of observations would you base your answers?
- Hint: Cross true breeding brown and white mice and and then interbreed their offspring. TO OBTAIN CREDIT YOU MUST draw the Punnett-squares for the F1 and F2 generations of each of the three different possibilities.
- A women with type A blood has a child with type O blood. She is suing a man with type B blood for child support, because she claims that man is the father of her child. How would you respond to the following statements.
- The attorney for the alleged father claims "The mother's blood is type A, so the child's type O blood must have come from the father. Because my client has type B blood, he can not be the father." Justify your answer with appropriate Punnett-square(s) or receive 0 points!
- The attorney for the mother claims "Because further tests prove he is heterozygous, he must be the father."
- Suppose expression of one allele of a Y-linked gene results in nonhairy ears in males. Expession of another allele results in rather long hairs, a condition known as hairy pinnae.
- Why would you NOT expect females to have hairy pinnae. Justify your answer with appropriate Punnett-square(s) or receive 0 points!
- A son of a hairy-eared male will also be hairy-eared. Explain why. Justify your answer with appropriate Punnett-square(s) or receive 0 points!
- In the figure (a pedigree diagram similar to figure 12.11), does the phenotype indicated by the dark circles and squares follow autosomal dominant, autosomal recessive or sex-linked (X recessive) inheritance? Explain fully why or why not for each of the three. Include the appropriate Punnett Squares to demonstrate the inheritance pattern expected for each of the
- Use Punnett-squares to show genotypes and phenotypes or receive 0 points!
- Kernel color in wheat plants is determined by two pairs of genes. Alleles of one pair show incomplete dominance over the other pair.
- For the gene pair at one locus on the chromosome, allele A1 imparts one dose of red color to the kernel, whereas allele
A2 does not. At the second locus allele B1 gives one dose of red color to the kernel, whereas
B2 does not. One kernel with genotype A1A1B1B1 is dark red. A different kernel with genotype
A2A2B2B2 is white. All other genotypes have kernel colors in between the two extremes.
- Suppose you cross a plant grown from a dark red kernel with a plant grown from a white kernel. What genotypes and phenotypes would you expect among the offspring?
- If a plant with genotype A1A2B1B2 self fertilizes, what genotypes and phenotypes would you expect among the offspring? In what proportions?