The formation of Gametes
1. Kelp, a large, multicellular type of algae, has air bladders in the blades to help them float near the surface of the ocean where they can get more sunlight. Assume that having many air bladders (M) is a dominant trait. What gametes would be produced by a heterozygous individual?
What gametes would be produced by a homozygous dominant individual?
2. In humans, sickle cell anemia is a disease caused by a mutation of a single locus gene which codes for an important blood protein. The allele for the normal protein (S) is dominant to that for the one causing sickle cell anemia. What gametes would be produced by an individual who suffers from sickle cell anemia?
What gametes would be produced by individuals resulting from a SS x ss cross?
3. In areas of the very deep and damp southeastern United States lives what is, for all intents and purposes, a giant flying cockroach known as a Palmetto bug. Assume that long antennae (L) are dominant to short antennae and that normal wings (N) are dominant to bent ones. What gametes will be produced by an individual that is homozygous dominant for antennae and heterozygous for wings?
What gametes will be produced by an individual that is heterozygous for antennae and homozygous recessive for wings?
4. In horses, the color black is due to a dominant allele (B) and chestnut color is due to the recessive allele (b). The trotting gait is due to a dominant allele (T) and the pacing gait to the recessive (t). What will be the gametes produced by a homozygous black pacer?
Suppose we cross the black pacer above with a homozygous chestnut trotter. What will be the gametes produced by the F1 generation?
5. Suppose you are designing a new Jurassic Park and you would like to have the crowd drawing presence of Velociraptor without the danger of having your crowds eaten. You have managed to come up with two varieties, very aggressive (A), which is apparently a dominant trait in Velociraptors, and non-aggressive. They also come in two colors, red (R), which is dominant, and green. At the moment you have a green female that is homozygous dominant for aggression and a non-aggressive male that is homozygous dominant for color. What gametes will be produced by the male and female?
Female:
Male:
What gametes will be produced by the F1 generation of these two Velociraptors (providing of course that the female doesn't dismember the male before mating)?
Bottom of Form
Monohybrid crosses
1. In dogs, wire hair (S) is dominant to smooth (s). In a cross of a homozygous wire-haired dog with a smooth-haired dog, what will be the phenotype of the F1 generation?
What would be the genotype?
What would be the ratio of wire-haired to smooth-haired dogs in the F2generation ?
2.Woodrats are medium sized rodents with lots of interesting behaviors. You may know of them as packrats. Let's assume that the trait of bringing home shiny objects (H) is controlled by a single locus gene and is dominant to the trait of carrying home only dull objects (h). Suppose two heterozygous individuals are crossed. How many of each genotype would be expected if only 4 offspring were produced?
How many of each phenotype?
3. Saguaro cacti are very tall cylindrical plants that usually have two L-shaped arms, one on each side. Suppose you lived in southern Arizona where the Saguaro cactus is common and you happen to have one growing in your yard. Your Saguaro has two arms but one is longer than the other. Now, assume that arm length in these cacti are controlled by a single gene with arms of the same length (A) being dominant to arms of different lengths. What is the genotype of your cactus?
Could one of the parents of your cactus have had a phenotype with arms the same length?
If so, what would have been the genotype of that parent?
Suppose you cross your cactus with that of your neighbor which has arms of the same length. Your great grandchildren (it takes a Saguaro cactus a long time to mature) find that half of the resulting offspring have arms the same length and half have arms of different lengths. What was the genotype of your neighbor's cactus?
4. The common grackle is a species of robin-sized blackbirds that are fairly common (hence the name) over most of the United States. Suppose that long tails (L) were dominant to short tails in these birds. A female short-tailed grackle mates with a male long-tailed grackle who had one parent with a long tail and one parent with a short tail. What is the male's genotype?
How many of each genotype will be found in the F1 generation (assume 4 offspring)?
How many of each phenotype will be found in the F1 generation?
5. The ability to curl your tongue up on the sides (T, tongue rolling) is dominant to not being able to roll your tongue. A woman who can roll her tongue marries a man who cannot. Their first child has his father's phenotype. What are the genotypes of the mother, father, and child?
What is the probability that a second child won't be a tongue roller?
Incomplete dominance
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. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?
What are the genotypic and phenotypic ratios of the F2generation?
2. 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. 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)?
What would be the genotypic ratio of the F1 generation (RR :Rr : rr)?
What genotypes would be produced by crossing a grasshopper with both color stripes and one with yellow stripes (choose all that apply)?
What phenotypes would be produced by crossing a grasshopper with both color stripes and one with yellow stripes (choose all that apply)?
3. Suppose you have two rose plants, both with pink flowers. You cross the two plants and are surprised to find that, while most of the offspring are pink, some are red and some are white. You decide that you like the red flowers and would like to make more. What cross would you perform to produce the most red flowered plants?
Your mother decides she would like some of the pink flowered roses. Which cross would give you the most pink flowered plants?
4. A naturalist visiting an island in the middle of a large lake observes a species of small bird with three distinct types of beaks. Those with short, crushing beaks (BB) consume hard shelled nuts, those with long, delicate beaks (bb) pick the seeds from pine cones, and those with intermediate beaks (Bb), consume both types of seeds though they are not as good at either. Assume that this difference in beak morphology is the result of incomplete dominance in a single locus gene. Which of the mated pairs below will have the best adapted offspring in a year in which most of the food available is in the form of hard shelled nuts?
What would be the phenotypic ratio of the F1 generation resulting from a cross of Bb x bb (Short:Intermediate:Long)?
How many offspring of an intermediate x short beak cross will have long beaks (assume 4)?
Dihybrid crosses
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 (choose all that apply)?
What percentage of the children will be albinos?
What percentage of the children will be non-tasters of PTC?
2. 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 (these are the dominant individuals who do most of the breeding) 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) living in the pack will have each of the following genotypes?
NNBB:Top of Form
NNBb: / Bottom of Form
Top of Form
NNbb: / Bottom of Form
Top of Form
NnBB: / Bottom of Form
Top of Form
NnBb: / Bottom of Form
Top of Form
Nnbb: / Bottom of Form
Top of Form
nnBB: / Bottom of Form
Top of Form
nnBb: / Bottom of Form
Top of Form
nnbb: / Bottom of Form
What percent of the offspring will be normal colored with blue eyes?
3. 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)?
What percentage of the offspring will lack mates because they have both slow head bobbing and yellow throats?
What percentage of the offspring will have trouble finding mates because because they lack one of the dominant traits?