1. In dogs, there is a hereditary deafness caused by a recessive gene, “d.” A kennel owner has a male dog that she wants to use for breeding purposes if possible. This dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd, the owner does not wish to use him for breeding so that the deafness gene will not be passed on. This can be tested by breeding the dog to a deaf female (dd). Draw the Punnett squares to illustrate these two possible crosses. In each case, what percentage/how many of the offspring would be expected to be hearing? deaf? How could you tell the genotype of this male dog? Also, using Punnett square(s), show how two hearing dogs could produce deaf offspring.

The following questions come from this website - you can go there to check your answers

  1. About 70% of Americans perceive a bitter taste from the chemical phenylthiocarbamide (PTC). The ability to taste this chemical results from a dominant allele (T) and not being able to taste PTC is the result of having two recessive alleles (t). Albinism is also a single locus trait with normal pigment being dominant (A) and the lack of pigment being recessive (a). A normally pigmented woman who cannot taste PTC has a father who is an albino taster. She marries a homozygous, normally pigmented man who is a taster but who has a mother that does not taste PTC. What are the genotypes of the possible children?
  1. In the breeding season, male Anole lizards court females by bobbing their heads up and down while displaying a colorful throat patch. Assume for this question that both males and females bob their heads and have throat patches. Assume also, that both traits are controlled by single locus genes on separate chromosomes. Now, suppose that anoles prefer to mate with lizards who bob their heads fast (F) and have red throat patches (R) and that these two alleles are dominant to their counterparts, slow bobbing and yellow throats. A male lizard heterozygous for head bobbing and homozygous dominant for the red throat patch mates with a female that is also heterozygous for head bobbing but is homozygous recessive for yellow throat patches. How many of the F1 offspring have the preferred fast bobbing / red throat phenotype (assume 16 young)?
  1. What percentage of the offspring will lack mates because they have both slow head bobbing and yellow throats?
  2. What percentage of the offspring will have trouble finding mates because they lack one of the dominant traits?
  1. Carrion beetles lay their eggs in dead animals and then bury them in the ground until they hatch. Assume that the preference for fresh meat (F) is dominant to the preference for rotted meat (f) and that the tendency to bury the meat shallow (S) is dominant to the tendency to bury the meat deep (s). Suppose a female carrion beetle homozygous dominant for both traits mates with a male homozygous recessive for both traits. What will be the genotype of the F1 generation?
  1. What will be the genotypic ratio of the F2 generation? Fill in the numbers before these genotypes - FFSS : FFSs : FFss : FfSS : FfSs : Ffss : ffSS : ffSs : ffss
  1. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are controlled by single locus genes and are located on different chromosomes. Assume further that normal coat color (N) is dominant to black (n) and brown eyes (B) are dominant to blue (b). Suppose the alpha male and alpha female of a pack are black with blue eyes and normal colored with brown eyes, respectively. The female is also heterozygous for both traits. How many of the offspring (assume 16 puppies) living in the pack will have each of the following genotypes?

NNBB:
NNBb:
NNbb:
NnBB:
NnBb:
Nnbb:
nnBB:
nnBb:
nnbb:
  1. In northeast Kansas there is a creature know as a wildcat. It comes in three colors, blue, red, and purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a heterozygous (Bb) individual is purple.
  2. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?
  3. What are the genotypic and phenotypic ratios of the F2generation?
  1. The lubber grasshopper is a very large grasshopper, and is black with red and yellow stripes. Assume that red stripes are expressed from the homozygous RR genotype, yellow stripes from the homozygous rr genotype, and both from the heterozygous genotype.
  2. What will be the phenotypic ratio of the F1 generation resulting from a cross of two grasshoppers, both with red and yellow stripes (red : both : yellow)?
  3. What would be the genotypic ratio of the F1 generation (RR : Rr : rr)?
  4. What genotypes would be produced by crossing a grasshopper with both color stripes and one with yellow stripes?
  5. What phenotypes would be produced by crossing a grasshopper with both color stripes and one with yellow stripes?
  1. A boy, whose parents and grandparents had normal vision, is color-blind. What are the genotypes for his mother and his maternal grandparents? Use XB for the dominant normal condition and Xb for the recessive, color-blind phenotype.
  1. The bison herd on Konza Prairie has begun to show a genetic defect. Some of the males have a condition known as "rabbit hock" in which the knee of the back leg is malformed slightly. We do not yet know the genes controlling this trait but for the sake of our question, we shall assume it is a sex-linked gene and that it is recessive. Now, suppose that the herd’s bull (the dominant one which does most of the breeding) who is normal (XN) mates with a cow that is a carrier for rabbit hock.
  2. What are his chances of producing a normal son?
  3. If he mates with this cow every year, what percentage of their daughters have normal knees?
  4. What percentage of their daughters will be carriers of rabbit hock?
  1. A rancher owns a bull with many desirable characteristics. Unfortunately, he also has a sex-linked trait that in the recessive form leads to no pigment formation in the iris of the eye. This makes the bull very sensitive to sunlight and could lead to blindness. The rancher wishes to breed him to a cow that will minimize the chances of any offspring showing this trait. She would especially like to produce another bull with most of his sire's desirable qualities but without the non-pigmented eye. Two cows with the dominant normal colored eyes (XN) are available that have been genetically typed for this particular trait. Cow 1 has a genotype of XN XN and cow 2 is XNXn.
  2. Which of these two cows should the rancher choose as a mate to her bull if she wishes to minimize the occurrence of the non-pigmented eye in his offspring?
  3. What percentage of the male offspring from the preferred cross will have non-pigmented eyes?
  4. Will crossing the bull with this cow eliminate the trait from the herd?
  5. If not, why not?
  1. Racoons have rings around their tails and a habit of washing their food in water before eating it. Suppose that both of these traits are controlled via incomplete dominance so that wide bands on the tail are BB, medium sized bands are Bb, and narrow bands are bb and that washing all their food is WW, washing some of their food is Ww, and washing no food is ww. How many of each genotype will be in the F1 generation resulting from a cross of two racoons, both with medium sized tail bands and that wash some of their food (assume 16)?

BBWW:
BBWw:
BBww:
BbWW:
BbWw:
Bbww:
bbWW:
bbWw:
bbww:
  1. How many of the F1 generation will have wide tail bands and won't wash any of their food?
  1. Clouded leopards are a medium sized, endangered species of cat, living in the very wet cloud forests of Central America. Assume that the normal spots (XN, pictured here) are a dominant, sex-linked trait and that dark spots are the recessive counterpart. Suppose as a Conservation Biologist, you are involved in a clouded leopard breeding program. One year you cross a male with dark spots and a female with normal spots. She has four cubs and, conveniently, two are male and two female. One each of the male and female cubs have normal spots and one each have dark spots.
  2. What is the genotype of the mother?
  3. Suppose a few years later, you cross the female cub that has normal spots with a male that also has normal spots. What genotypes will be found in the cubs? (assume 4 cubs are produced)

Some more problems to ponder

  1. Marian’s father is colorblind, as is her maternal grandfather (her mother’s father). Marian herself has normal color vision. Marian and her husband, Martin, who is also colorblind, have just had their first child, a son they have named Mickey. Please answer the following questions about this small family.
  2. What is the probability that this child will be colorblind?
  3. Three sources of the colorblindness allele are mentioned in this family. If Mickey is colorblind, from which of these three men (Marian’s grandfather, Marian’s father, or Martin) did he inherit the allele?
  4. Using proper pedigree format, diagram the available information about the four generations of this family described, assuming that Mickey is colorblind.
  5. If Martin were not colorblind, how would this affect the prediction about Mickey?
  1. In cats, there is a gene located on the X chromosome that determines coat color. This gene has two alleles—orange and black. Assume black is the dominant allele and orange is the recessive allele. A heterozygous cat has tortoiseshell color (a splotchy mixture of orange and black). List the genotypic and phenotypic frequencies among the offspring of the following crosses. Pay careful attention to the genders of the offspring.
  2. Black female X Orange male
  3. Orange female X Black male
  4. Tortoiseshell female X Black male
  5. Tortoiseshell female X Orange male
  1. In a particular family, one parent has Type A blood, the other has Type B. They have four children. One has Type A, one has Type B, one has Type AB, and the last has Type O. What are the genotypes of all six people in this family?

NOTE: The ABO blood type gene has three alleles. IAand IBare co-dominant; i (for Type O) is recessive to both.

  1. Mrs. Smith has blood type A. Mr. Smith has blood type B. Their first child has blood type AB. Their second child has blood type O. What are Mr. and Mrs. Smith’s genotypes for these two genes?
  1. In a recent case in Spokane, Washington, a young woman accused a soldier of being the father of her child. The soldier, of course, denied it. The soldier’s lawyer demanded that blood types be taken to prove the innocence of his client. The following results were obtained: Alleged father, Type O. Mother, Type A. Child, Type AB. The court found the soldier guilty on the basis of the woman’s remarkable memory for dates and details that apparently eliminated all other possible fathers.
  2. What are the possible genotypes for these three people?
  3. Do you agree with the court’s decision? Why or why not?
  1. It was suspected that two babies had been exchanged in a hospital. Mr. and Mrs. Jones received baby #1 and Mr. and Mrs. Simon received baby #2. Blood typing tests on the parents and the babies showed the following:

Mr. Jones: Type A / Mr. Simon: Type AB
Mrs. Jones: Type O / Mrs. Simons: Type O
Baby #1: Type A / Baby #2 Type O

Were the babies switched? How do you know whether they were or they weren’t?

  1. In cats, there is a gene which produces ticked fur (bands of different colors on each hair) called Agouti (H). The recessive allele (h) for this gene produces hair which is a solid color from end to end (i.e. hh). In addition, there is a coat color gene which has a recessive albino allele (a) which, in the homozygote, prevents the production of any coat color pigment, resulting in a white cat with pink eyes, the traditional albino. Note that this problem describes two completely different genes. These genes are unlinked. An albino female cat is mated to a solid brown male cat. All of their offspring have Agouti fur. The males and females among these offspring are allowed to freely inter-mate, producing a flock of F2 kittens. What will be the genotypes and phenotypes for these grandkittens. What is the phenotypic ratio for these grandkittens.

Try this one – it’s a bit complicated but give it a try anyway and see what happens

In Drosophila (fruit flies), the wild type eye color, brick red, is actually produced by the deposition of two pigments in the eyes, a dull brown pigment and a brilliant red pigment. These two pigments are produced by the action of two different, non-allelic (and non-linked) genes. Each of these genes has two alleles, a dominant one which causes normal the production of the pigment controlled by the gene, and a recessive one which is defective, and causes none of that pigment to be produced. Thus, a normal eye-color fruit fly must have at least one dominant allele for each of these genes.

If a fly is homozygous for the defective, recessive allele of the gene which produces the brown pigment, that fly will have only the brilliant red pigment in its eyes. This condition is called “cinnabar.” For this reason, the gene responsible for producing the brown pigment is called the “cinnabar” gene (genes are often named for the effect their mutant alleles have on the phenotype). The symbol for this gene is a two-letter symbol, cn. The dominant allele is Cn and the recessive allele is cn. Careful with this symbol. Never separate the c’s from the n’s. So a cinnabar-eyed fly would have the genotype cn cn.

If a fly is homozygous for the defective, recessive allele of the gene which produces the brilliant red pigment, that fly will have only the dull brown pigment in its eyes. This produces “brown” eyes, so this gene is called the “brown” gene. The symbol for this gene is br. The dominant allele is Br, the recessive br. A brown-eyed fly would be br br. Again, be careful not to separate the b and the r.

Note that all flies have two alleles for each of these genes, so the cinnabar eyed fly would actually have the genotype cn cn Br Br or cn cn Br br, and the brown eyed fly would actually have the genotype Cn Cn br br or Cn cn br br.

A mating is made between a Cn Cn br br fruit fly and a cn cn Br Br fruit fly. 200 offspring result (the F1). These offspring are allowed to freely interbreed, and produce 40,000 (whew! Whatever happened to population control!) offspring (the F2).

  1. What color eyes did the original parents have?
  2. What were the genotypes and phenotypes of the F1 offspring?
  3. What color eyes do the cn cn br br flies have?
  4. What phenotypic ratio do you predict among the F2 offspring?