Name: ______
SHOW ALL WORK!
Monohybrid Crosses
1) In tomatoes, tall stature (T) is dominant over dwarf stature (t). If you cross a homozygous tall plant with a homozygous dwarf plant in the parental generation, what would the phenotypic and genotypic ratios of the F1 progeny (offspring) be?
If the F1s were crossed, what would the genotypic and phenotypic ratios of the progeny be? What would this generation be called?
2) What genotype would you cross the tall plants obtained in the F1 generation with in order to determine if they were homozygous or heterozygous? What is this type of cross called? Show your work to gain a better understanding of this concept.
3) In guinea pigs black coat (B) is dominant over white coat (b). In a cross between two black coated guinea pigs, the following progeny were obtained:
8 black coated guinea pigs
3 white coated guinea pigs
From these data, determine the genotypes of the parents of the guinea pigs produced from this cross.
4) One day while perusing the grapes at my local Safeway store, I spied a mutant fruit fly that had no wings. This trait is called vestigial (vg) by fruit fly geneticists and is recessive to the wild type allele for normal wings (+). So, I captured the little devil and decided to cross this vestigial fly with one of my prized normal winged flies. All of the progeny from this cross have normal wings. What is the genotype of my prized normal winged fly? If I were to cross two of the F1s, what would the expected genotypic and phenotypic ratios of the F2 generation be?
5) The ability to taste a bitter chemical, phenylthiocarbamide (PTC), is due to a dominant allele in humans. In terms of tasting ability, what are all of the possible phenotypes of a man both of whose parents were tasters? What are his possible genotypes? Use T for the designation of the dominant allele and t as the designation of the recessive allele.
6) All of the progeny produced in a cross between a spotted rabbit and a solid-colored rabbit are spotted. When these F1 rabbits are crossed among themselves, they produced 23 spotted rabbits and 8 solid-colored rabbits. a) Which of the alleles in rabbits is dominant? b) About how many of the 23 spotted rabbits in the F2 will be homozygous? c) How many solid colored progeny would be homozygous?
7) In snapdragons, the alleles for flower color exhibit an incomplete dominance between the two alleles (red, Cr, and white, Cw). The floral color of a heterozygous plant is pink as these flowers have less red pigment than homozygous red plants. What offspring are produced from a cross of a heterozygous plant and a homozygous white flowered plant?
8) The palomino horse is golden in color. Unfortunately, for horse fanciers, palominos do not breed true. In a series of matings between palominos, the following offspring were obtained:
65 palominos, 32 cream-colored horses, 34 chestnut (reddish-brown) horses
What is the probable mode of inheritance of palomino coloration?
9) The ABO blood system of human blood typed are determined by 2 of 3 alleles (IA, IB, i). The A and B alleles are codominant and both are completely dominant over the recessive o allele. What are the potential blood types of the offspring produced by a female with blood type A (genotype IA i) and a male with blood type B (genotype IB i)?
Dihybrid Crosses
10) For the following parental genotypes indicate the potential gamete types.
Genotype Gamete types
AABB
AaBb
Aabb
AABb
aaBb
11) In tomato plants, tall plant alleles (D) are dominant over dwarf plant alleles (d), and red fruited alleles (Y) are dominant over yellow fruited alleles (y). A homozygous tall, red-fruited plant is crossed with a homozygous dwarf, yellow-fruited plant. What are the potential types and proportions of offspring from this cross?
What is the outcome if two plants from the F1 generation are crossed?
12) How would you determine the genotype of a tall, red-fruited tomato plant?
What would be the results of the test-cross if the tall, red-fruited plant was:
homozygous for both genes?
heterozygous for only height?
heterozygous for only fruit color?
heterozygous for both genes?
13) In dogs, 1 gene determines whether a dog barks or is silent when trailing. The allele (B) for barking is dominant over the allele (b) for silent trailers. Also, erect ears (E) are dominant over drooping ears (e).
What kinds of pups (and in what proportions) would be expected from a cross between a heterozygous, erect-eared barker, and a droop-eared, silent trailer?
14) In humans, the allele for tongue rolling (T) is dominant for the non-tongue rolling allele (t), and the allele for non-ear wiggling (W) is dominant over the ear wiggling allele (w). What are the expected results of a cross between an ear-wiggling, heterozygous tongue roller, and an heterozygous non ear wiggling, homozygous tongue roller?
15) In humans, hair color is controlled by two interacting genes. The same pigment, melanin, is present in both brown-haired and blond-haired people, but brown hair has much more of it. Brown hair (B) is dominant over blonde hair (b). Whether any melanin can be synthesized depends on another gene. The dominant form (M) allows melanin synthesis; the recessive form (m) prevents melanin synthesis. Homozygous recessive (mm) individuals are albino. What will be the expected genotypic and phenotypic proportions in the children of the following parents: double heterozygous brown-haired mother and blonde-haired heterozygous melanin production (Mm) father?
16) In some situations, a gene at one location affects the expression of a gene at another location. In poultry, the type of comb is genetically determined by two genes (R or r, and P or p) in an epistatic condition. The allele for a rose comb (R) is dominant over the allele a single comb (r) and the allele for a pea comb (P) is dominant over a single comb (p). When the poultry has at least one dominant allele for both traits it has a walnut comb. The following table lists the phenotypes and the associated genotypes of this epistasis.
Single comb / Pea comb / Walnut Comb / Rose Comb(rrpp) / (rrPP or rrPp) / (RRPP, RRPp, RrPP, RrPp) / (Rrpp or RRpp)
What would you predict about the types of combs among the offspring of two heterozygous walnut-combed fowl?
Sex-Linked Problems
17) One of the genes for baldness is located on the X chromosome and is recessive to the allele for normal hair at the same gene. If a bald male were to marry a carrier female, what would be the probability that the first born son would be bald? What percentage of the females produced in this liaison would be carriers?
18) Dave is color blind. Color blindness is sex-linked and the allele which is responsible for this driving menace is recessive to the allele for normal color vision. Judith, Dave’s wife, has normal vision. Dave and Judith had twelve offspring, all of which had normal vision. Their children were equally distributed as to sex. What is Judith’s most likely genotype? Could she be a carrier? Why or why not?
19) The gene for hemophilia, the inability of the blood to clot, is located on the X chromosome. The allele for normal clotting (H) is dominant over the hemophiliac allele (h) and females who are heterozygous for this gene are said to be carriers. In a cross between a phenotypically normal female and a normal male, who had a rather large family I might add, the following offspring were observed:
5 normal females, 2 hemophiliac males, and 3 normal males
What was the genotype of the mother? What are the possible genotypes of each of the females produced through these matings? What is the genotype of the normal males?
20) A carrier female and a normal male have 1 child. What is the probability that this child is a carrier of hemophilia? What is the probability the child is a hemophiliac? What is the probability that the child is a male?
21) A) In humans, one of the genes determining color vision is located on the X chromosome. The dominant form (C) produces normal color vision; red-green color blindness (c) is recessive. If a man with normal color vision has children a color-blind woman, what is the probability of their having a color-blind son? What is the probability of their having a color-blind daughter?
B) In the couple described in A) above, the woman gives birth to a color-blind daughter. The man sues for divorce claiming the woman was unfaithful to him and committed adultery. Based on your answers above will his case stand up in court? Explain your answer.