Exam 5: Extensions and Modifications of Basic Principles

In some plant species, a single pair of alleles is involved in both flower color and stem color. For example, a plant with red flowers may also have red stems, whereas white-flowered varieties of the same species have green stems. How would you explain this observation?

Male-limited precocious puberty results from a rare autosomal allele (P) that is dominant over the allele for normal puberty (p) and is expressed only in males. A male and female that both went through normal puberty have two sons. The first son undergoes precocious puberty but the second undergoes normal puberty. -What is the genotype of the mother?

In purple people eaters, purple is dominant to white. A true-breeding white mutant is mated with a different true-breeding white mutant. All of the F₁ are purple. When the purple F₁ offspring mate with each other, their offspring occur in the ratio of 9 purple : 7 white. Which phenomenon explains the purple F₁ offspring?

In a certain species of plant, flowers occur in three colors: blue, pink, and white. A pure-breeding pink plant is mated with a pure-breeding white plant. All of the F₁ are blue. When the blue F₁ plants are selfed, the F₂ plants occur in the ratio 9 blue : 3 pink : 4 white. The genotype that produces white is ww. The presence of one W allele allows pink or blue color to occur. The alleles at the hypostatic locus are B (blue) and b (pink). - What is the genotype of the F₁ plants?

What phenomenon describes a genetic trait that is expressed more strongly or earlier in development with each generation?

In rabbits, an allelic series helps to determine coat color: C (full color), c^ch (chinchilla; gray color), c^h (Himalayan; white with black extremities), and c (albino; all white). The C allele is dominant to all others, c^ch is dominant to c^h and c, c^h is dominant to c, and c is recessive to all the other alleles. This dominance hierarchy can be summarized as C > c^ch > c^h > c. -Indicate the phenotypic ratios expected of rabbits with the cross Cc^h × c^hc.

Coat color is determined by two loci, A and B, in large cats. Two pink panthers fall in love and produce a large litter of baby panthers with the following phenotypic ratios: 12/16 pink; 3/16 black; and 1/16 white. - What is the genotype of the white progeny?

In a certain species of plant, flowers occur in three colors: blue, pink, and white. A pure-breeding pink plant is mated with a pure-breeding white plant. All of the F₁ are blue. When the blue F₁ plants are selfed, the F₂ plants occur in the ratio 9 blue : 3 pink : 4 white. -What is the name for this type of interaction?

Which of the following is a characteristic exhibited by cytoplasmically inherited traits?

Hair color is determined in Labrador retrievers by alleles at the B and E loci. A dominant allele B encodes black pigment, whereas a recessive allele b encodes brown pigment. Alleles at a second locus affect the deposition of the pigment in the shaft of the hair; dominant allele E allows dark pigment (black or brown) to be deposited, whereas recessive allele e prevents the deposition of dark pigment, causing the hair to be yellow. - A black female Labrador retriever was mated with a yellow male. Half of the puppies were black and half were yellow. If the genotype of the black female parent was Bb Ee, then what was the genotype of the other parent?

The R locus determines flower color in a new plant species. Plants that are genotype RR have red flowers, and plants that are rr have white flowers. However, Rr plants have pink flowers. What type of inheritance does this demonstrate for flower color in these plants?

You are studying body color in an African spider and have found that it is controlled by a single gene with four alleles: B (brown), b^r (red), b^g (green), and b^y (yellow). B is dominant to all the other alleles, and b^y is recessive to all the other alleles. The b^g allele is dominant to b^y but recessive to b^r. You cross a pure-breeding brown spider with a pure-breeding green spider. -Predict the phenotype of the progeny.

Which organelle in an animal cell, in addition to the nucleus, contains genes?

In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. -Give genotypes for comb shape of the parents in the following cross: Pea crossed with single produces 1 single offspring.

In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. - Give genotypes for comb shape of the parents in the following cross: Walnut crossed with single produces 1 walnut, 1 rose, 1 pea, and 1 single offspring.

Assume that a polygenic character in Drosophila is produce through the activity of five genes, each with two alleles. Two individuals who are both heterozygous for all five genes are crossed. How many different genotypes are expected in the offspring?

Coat color is determined by two loci, A and B, in large cats. Two pink panthers fall in love and produce a large litter of baby panthers with the following phenotypic ratios: 12/16 pink; 3/16 black; and 1/16 white. -What is the genotype of the pink progeny?

With regard to the ear shape phenotypes described in the previous question, how could you test the relative importance of environmental and genetic factors?

In domestic chickens, some males display a plumage pattern called cock feathering. Other males and all females display a pattern called hen feathering. Cock feathering is an autosomal recessive trait that is exhibited in males only. -Two heterozygous birds are mated. What fraction of the male offspring is expected to exhibit cock feathering?

The SRY gene is located on the Y chromosome. This single gene encodes a protein called a transcription factor that binds to DNA and stimulates the transcription of other genes that lead to the development of male sex characteristics, including physical, biochemical, and behavioral phenotypes. What concept in genetics BEST describes this example?